Research - Plants, Trees,
Secret life of plants
From memory to intelligence
Stanislaw Karpinski1 and Magdalena Szechynska-Hebda1,2
Plants are able to perform photosynthesis and cannot escape from environmental stresses, so they therefore developed sophisticated, highly responsive and dynamic physiology. Others' and our results indicate that plants solve their optimal light acclimation and immune defenses, photosynthesis and transpiration by a computational algorithm of the cellular automation. Our recent results however suggest that plants are capable of processing information encrypted in light intensity and in its energy. With the help of nonphotochemical quenching and photoelectrophysiological signaling (PEPS) plants are able to perform biological quantum computation and memorize light training in order to optimize their Darwinian fitness. Animals have their network of neuron synapses, electrophysiological circuits and memory, but plants have their network of chloroplasts connected by stromules, PEPS circuits transduced by bundle sheath cells and cellular light memory. It is suggested that plants could be intelligent organisms with much higher organism organization levels than it was thought before.
Source : Plant Signaling and Behavior
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Therapeutic effect of forest bathing on human hypertension in the elderly
- Gen-Xiang Mao, MDa,
- Yong-Bao Cao, MBa, 1,
- Xiao-Guang Lan, BAb,
- Zhi-Hua He, BAb,
- Zhuo-Mei Chen,PhDc,
- Ya-Zhen Wang, MMa,
- Xi-Lian Hu, PhDa,
- Yuan-Dong Lv, MBa,
- Guo-Fu Wang, PhDa, , ,
- Jing Yan, MMa,
ObjectiveTo provide scientific evidence supporting the efficacy of forest bathing as a natural therapy for human hypertension.
Methods Twenty-four elderly patients with essential hypertension were randomly divided into two groups of 12. One group was sent to a broad-leaved evergreen forest to experience a 7-day/7-night trip, and the other was sent to a city area in Hangzhou for control. Blood pressure indicators, cardiovascular disease-related pathological factors including endothelin-1, homocysteine, renin, angiotensinogen, angiotensin II, angiotensin II type 1 receptor, angiotensin II type 2 receptor as well as inflammatory cytokines interleukin-6 and tumor necrosis factor α were detected. Meanwhile, profile of mood states (POMS) evaluation was used to assess the change of mood state of subjects. In addition, the air quality in the two experimental sites was monitored during the 7-day duration, simultaneously.
Results The baselines of the indicators of the subjects were not significantly different. Little alteration in the detected indicators in the city group was observed after the experiment. While subjects exposed to the forest environment showed a significant reduction in blood pressure in comparison to that of the city group. The values for the bio-indicators in subjects exposed to the forest environment were also lower than those in the urban control group and the baseline levels of themselves. POMS evaluation showed that the scores in the negative subscales were lowered after exposure to the forest environment. Besides, the air quality in the forest environment was much better than that of the urban area evidenced by the quantitative detection of negative ions and PM10 (particulate matter <10 μm in aerodynamic diameter).
Conclusion Our results provided direct evidence that forest bathing has therapeutic effects on human hypertension and induces inhibition of the renin–angiotensin system and inflammation, and thus inspiring its preventive efficacy against cardiovascular disorders.
Source : European Journal of Integrative Medicine
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Forest adjuvant anti-cancer therapy to enhance natural cytotoxicity in urban women with breast cancer: A preliminary prospective interventional study
Studies have shown both significantly diminished natural cytotoxicity and immunosuppression in breast cancer patients after standard anti-cancer treatments. Therefore, an integrative approach employing adjuvant therapy in addition to current treatments is required to enhance immunoactivation. This preliminary prospective interventional study aimed to assess the feasibility of forest therapy as an adjuvant to enhance natural cytotoxicity.
Methods This was a feasibility study of 11 volunteer women aged 25–60 years with stage III breast cancer. All subjects were exposed to daily forest therapy for 14 days whilst living in accommodation in a forest. Interventions included a relaxing daily 2-h morning walk (3 miles), free time tailored to subjects interest, group interaction and prepared meals based on nutritional standards. Outcome measures included natural killer (NK) cell populations and levels of perforin and granzyme B.
Results Data from all participants were analysed. The mean volume of NK cells increased from 319.4 μL in the city to 444.6 μL in the forest after forest therapy (p < 0.01). The mean level of perforin increased from 216.9 pg/mL in the city to 344.9 pg/mL in the forest and then further increased to 463.2 pg/mL after subjects returned to the city (p < 0.02). The mean level of granzyme B increased from 4.4 pg/mL in the city to 11.2 pg/mL in the forest and then further increased to 20.2 pg/mL after subjects returned to the city (p < 0.02).
Conclusions This study demonstrates the potential of forest therapy as an adjuvant anti-cancer therapy after standard treatments. A definitive trial with a control group should now be performed with larger sample sizes and long-term follow-up periods to confirm the feasibility and potential therapeutic effectiveness of this approach.
Source : European Journal of Integrative Medicine
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The future of tree health
Ancient mainstays of our woodlands, hedgerows and parklands are at risk from a surge of pests and diseases - but a new research programme is bringing experts together from many fields to find solutions.
Chalara fraxinea - the fungus behind ash dieback - was first spotted in the UK in early 2012 in a consignment of trees from the Netherlands. It had already spread widely, and it's now almost certainly present throughout much of Britain.
It's already devastated European ash populations across the Continent since arriving in the early 1990s. Some trees can resist it, but most can't. Ash accounts for around 13 per cent of UK broadleaf cover, so dieback could change the landscape as profoundly as Dutch elm disease did a generation ago. Right now there's no defence and no cure.
A major research programme is helping us understand and control this woodland catastrophe, and perhaps even prevent the next one; in an increasingly globalised world, the flow of new pests and diseases is only likely to increase. Tom Marshall spoke to some of the scientists working under the Tree Health and Plant Biosecurity Initiative.
Population biology to control diseaseChalara is spreading fast - but what will its long-term effects be? Will it fizzle out, reduce the ash to a minor hedgerow shrub, or even drive it to extinction? It all depends on how the fungus and its host's defences evolve.
Professor James Brown of the John Innes Centre is focusing on the fungus's pathogenicity - its capacity to harm its host. Some Chalara strains are deadlier than others, but does this extra investment in pathogenicity weaken the fungus in other areas, like reproducing or surviving cold winters? If there's a high cost to being deadly, there's a good chance the ash population will make a long-term recovery as tree defences evolve.
Brown also wants to understand the fungus population's genetic structure, to see how natural selection acts on that population - the more genetic variation it contains, the faster it can evolve to beat ash trees' defences.
'Understanding variation in the fungus's pathogenicity will tell us about the long-term prospects for the ash population developing resistance,' says Brown. If the fitness cost turns out to be very high, we might be able to rely on natural selection alone - though in practice we may want to speed up the process. Brown's project could show how to breed more resistant ashes or manage woodlands to encourage the spread of disease-resistant genes.
It may also help contain the disease in the shorter term. The group is examining a related but harmless fungus that arrived in the 19th century and is now widespread in UK ashes. If the two fungi are close enough to share genes and diseases, viruses that infect the naturalised fungus could be transferred to the newcomer to slow its spread.
Genomics for more resistant treesThe European ash may be in trouble but Dr Richard Buggs at Queen Mary, University of London thinks the solution could already be in the ash family's genes. Some close relations aren't bothered by the ash dieback fungus at all - for example in Manchuria it's been around for a long time but doesn't seem to harm living trees.
Buggs has already sequenced the European ash genome (see www.ashgenome.org) and now he's doing the same for 35 different ash species from all over the world. His research group will analyse the results to identify which genes confer disease resistance. We may be able to transfer those genes into the European ash, with regular breeding techniques or even using genetic modification (GM) technology.
Social scientists are investigating what people think of the different options, and which they'd be prepared to accept. 'We don't want to spend many years creating a wonderful new genetically modified disease-resistant ash tree, only to find the public isn't willing for us to plant it,' Buggs says.
He'd like to make sure the ultimate result is resistant not just to Chalara, but also to the emerald ash borer - an even deadlier threat that's moving across Eurasia and could reach the UK in the next decade or two. It would be tragic if scientists could deal with the danger dieback poses to our ashes just in time for a new pest to arrive and finish them off.
Biological pest controlProfessor Tariq Butt of Swansea University specialises in biological insect control - killing pests using other organisms. He's an expert on Metarhizium anisopliae, a fungus that's raised killing insects to a fine art. Unlike chemical pesticides, it's lethal to the intended victim but harmless to other insects and the wider environment.
This could be critical to our trees' future, because damaging invasive insects are already loose in our woodlands, and others are likely to follow.
The initial focus is the pine processionary moth, now found across much of Europe although not, for the moment, in the UK. Its caterpillars stunt tree growth, potentially devastating timber profits.
They're also covered in stinging hairs that can detach and blow on the wind, causing swelling and extreme pain and making it risky just to walk in the woods. They can even cause blindness if they get in a victim's eyes; two of Butt's collaborators in Turkey have already been hospitalised after a fieldwork accident.
The researchers are working on lures to get moths into Metarhizium traps. One idea is attracting males with female pheromones; another is using tree signalling chemicals to make females think they've found the perfect spot to lay their eggs.
Similar techniques should work on many pests, like vine weevils and the Asian longhorn beetle. Butt is working with forestry companies and other organisations including the Food and Environment Research Agency (Fera) and the Forestry Commission.
'We take trees for granted, but if major species start disappearing from the landscape it will have a huge psychological impact on us all,' says Butt. 'Even if we eventually find solutions that lets them return, a landscape full of saplings just won't be the same.'
The economics of ash diebackPlanting woodland is a long-term gamble; it's not like sowing a field of wheat, where the risks are short-lived and if the crop fails you may be able to recoup your losses next year. The chances of eventual profit have to be weighed against many risks - from a drop in the price of wood to disease destroying the plantation.
Dr Adam Kleczkowski of the University of Stirling is leading a team of mathematicians, forest ecologists and economists to understand how disease affects foresters' decision-making, and how ash dieback is changing this. For example, will they stop planting ash - or could they plant more, hoping for a crop before the disease reaches them? We don't know, and we need to if we're to grasp the disease's long-term effects.
'More diseases will appear, and to deal with them we have to stop reacting afterwards and start preparing before problems occur,' Kleczkowski notes. 'We have to be more proactive in finding solutions.' And with around half of UK forests in private hands, we need economic solutions as well as political ones.
Kleczkowski plans to identify the forces affecting the spread of tree pathogens including ash dieback, and use these to improve models of economic decision-making so they account for the presence of disease. This should illuminate the behaviour of foresters and woodland managers faced with trade-offs between disease risk and other factors.
All this will deepen our understanding of dieback's economic dimensions, and of how it affects already-complex decision-making. Some of its costs are easy to measure - lost carbon credits, destroyed timber crops. Others, like reduced enjoyment of woodlands, are subtler; the scientists will carry out experiments asking people to choose between different outcomes to get a clearer idea of how much they value these intangible benefits.
At the project's end, Kleczkowski aims to have a list of potential anti-disease policies, ranked by cost-effectiveness. This will include things we already do and potential ideas for the future; it will help policymakers plan the war on plant pathogens for the long term.
An ecosystem approach to tree healthDr Stephen Cavers at the Centre for Ecology & Hydrology leads a project that focuses on pest and disease resistance in the Scots pine. The UK's only native pine, it's economically valuable and ecologically priceless - the cornerstone of the rare Caledonian pinewood habitat, sole remnant of the primordial forests that once covered Britain.
Like several other species, Scots pines are under severe pressure from red band needle blight, a potentially fatal disease which has become a widespread and serious threat in Britain. But this is only one of several challenges they face in the coming years, from insect pests to climate change. The project will investigate how natural genetic variation can help the trees cope.
'Tree health depends on many different things, not just the particular pathogens,' says Cavers. 'Today, with climate change and new pests and diseases on the way, it's important to study it from several different angles simultaneously.'
The way a tree looks and grows depends on genes - its genotype - and the local environment. As natural selection acts, some genotypes do better than others. Yet if the environment changes - for example, if the climate gets warmer or we move seeds from one place to another - then once-successful genotypes can become stressed and susceptible to disease.
Individuals within a species vary in their ability to cope with these complex environmental pressures. This variation could point to solutions, if we know enough about how trees relate to their whole ecosystem - including pests and diseases.
For instance, assessing the tree's microbiome - the tiny organisms living on and in its leaves, which may act like a human's beneficial gut bacteria - will reveal if and how it affects disease risk.
Cavers will also consider how Scots pine is grown and managed, working with landowners, foresters and others to increase awareness of tree-health issues, and find ways to apply science to tree management. 'We want to produce guidelines on how to use natural variation to minimise the impact of disease on many tree species,' he adds. 'By looking at many health issues together, we think we can come up with helpful guidance for conservationists, foresters and the general public.'
Better biosecurity through technologyAn interdisciplinary group led by Dr Rick Mumford of the Food and Environment Research Agency (Fera) is building technologies to help stop pests and pathogens at the border, or at least detect them before they spread too far.
Insects and fungal spores can get to the UK naturally, but many arrive in plant shipments, so monitoring imports is essential. Two technologies will help inspectors at ports: an electronic 'nose' that can detect volatile chemicals emitted by many infected plants; and cameras that pick up subtle disease-induced changes by looking beyond the spectrum of visible light. Both can detect many problems long before they are visible to the naked eye.
Other projects aim to give early warning of pests and diseases in the wild to improve our chances of stopping them getting a foothold. 'Monitoring imports is vital, but it's a thin blue line around the country,' Mumford notes. 'If a new disease gets through it can be several years before we find out, and in that time it can spread a long way. We need better surveillance technology.'
His group aims to create systems that capture fungal spores and test for the DNA of known pathogens; detectors to pick up the genetic material of waterborne diseases like sudden oak death; and smart insect traps that catch invasive species with customised lures and then transmit images to base for identification. The researchers are working with citizen-science experts at the Centre for Ecology & Hydrology to create risk maps to guide trap placement, drawing on the expertise of amateur entomologists.
Many of these technologies have already been developed in areas like homeland security, where they're used to detect explosives, drugs and other illegal items. Others are widely-used scientific instruments. The challenge is turning them from research tools into portable devices that are easy for plant inspectors, foresters and others to use in the field.
What do we really think of tree health?The arrival of ash dieback has triggered heated debate in the media and beyond, and many of us now know enough about tree health to report sightings and take steps to avoid spreading disease.
But there's still a lot we don't know about public understanding of tree-health risks - and about the social, cultural and economic factors that shape it. Dr Clive Potter at Imperial College London is exploring how people encounter tree pests and diseases in different contexts, and assessing the role the media and other communication channels play in informing people of the risks they pose.
They'll study public reaction to, and involvement with, three recent outbreaks in the UK - ash dieback, sudden oak death and the oak processionary moth. Their findings will help build public trust in initiatives like Defra's Plant Health Risk Register, which assesses threats to UK flora. They'll also help policymakers and risk managers find better ways to communicate with the public, making the issues relevant and help people understand how they can make a difference.
Source : Planet Earth Online
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Who says heroes have to be human? U.S. trees save more than 850 lives a year
A new study reveals eye-opening statistics about the health benefits of our arboreal cohabitants.
While trees are just standing around – swaying in the breeze and providing shade – they are also up to some seriously noble work. While most of us know that trees take in carbon dioxide and release oxygen, they are quietly providing another important service as well. Namely, they remove deleterious pollutants from the air, according to new research from the United States Forest Service.
The study, led by Dave Nowak and Eric Greenfield of the Forest Service's Northern Research Station along with collaborators from the Davey Institute, found that trees are actively diminishing air pollution. The researchers examined four pollutants in particular: nitrogen dioxide, ozone, sulfur dioxide and particulate matter less than 2.5 microns (PM2.5) in aerodynamic diameter. Health problems from these pollutants include harm to pulmonary, cardiac, vascular, and neurological systems. In the U.S., an estimated 130,000 deaths were related to PM2.5 and another 4,700 to ozone in 2005.
The scientists looked at how trees remove air pollution by the interception of particulate matter on plant surfaces and the absorption of pollutants through the leaf stomata; they concluded that trees in the U.S. are saving the lives of more than 850 Americans a year. And that’s not all – they are preventing 670,000 incidents of acute respiratory symptoms and saving us a whopping $7 billion a year in health costs by reducing respiratory illness.
And all that just by improving air quality by less than 1 percent.
Not surprisingly, the amount of trees in an area has an affect on the benefits. While the average tree cover in the country is estimated at 34.2 percent overall, it ranges by area from 2.6 percent in North Dakota to 88.9 percent in New Hampshire.
“In terms of impacts on human health, trees in urban areas are substantially more important than rural trees due to their proximity to people,” Nowak said. “We found that in general, the greater the tree cover, the greater the pollution removal, and the greater the removal and population density, the greater the value of human health benefits.”
The study was published in the journal Environmental Pollution.
Source : MNN
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How plants may be evolving to the lack of bees
Plants which used to have two types of male reproductive organs – to increase their chances for fertilisation – are reverting back to one type. And in some cases, they are becoming self-fertilising.
This "reverse evolution" could provide new hope for people worried about declining numbers of pollinators, such as bees.
Researchers from the University of Stirling and the University of Illinois turned their attention on the buffalo bur, a prickly species from Mexico and North America. It's part of the same family of "nightshade" plants as the tomato and the humble potato.
The bur has evolved unusual flowers with two types of male reproductive organs – or anthers.
"One type of feeding anther has evolved to lure pollen-eating bees, whilst another pollinating anther sneaks behind the bees' backs and deposits pollen for fertilising other flowers", says Dr Mario Vallejo-Marín from Stirling's School of Natural Sciences.
"This elaborate pollination strategy has evolved multiple times in bee-pollinated flowers of many plant families, and is an example of how natural selection can produce the similar results from different starting points."
But he adds: "Evolution sometimes reverses on itself. We've discovered that this complicated division of labour within flowers can breakdown repeatedly, and produce species with flowers that revert back towards the ancestral form of only one type of anthers."
In a study, published in the Royal Society journal Philosophical Transactions of the Royal Society B, the researchers say this "reversion" to smaller flowers – with one functional type of anthers – may be caused by the loss of pollinators (such as bees) of the right size required to fertilise the flowers.
Competition for pollination between closely related species can also be a factor.
"Plants can dynamically adapt to changing numbers and types of pollinating bees," says Dr Vallejo-Marín, "A loss of pollinating bees may favour the evolution of smaller, self-fertilising flowers that don't require pollinators."
The buffalo bur is regarded as a weed – and an invasive species in some countries. But falls in bee numbers are a bigger worry for other crops.
"Whether the reversion towards self-fertilisation can provide an escape route from ecological bee shortages depends on how rapidly plants can evolve. In the current pollinator crisis, understanding how plants adapt to changes in bee numbers and type is essential."
Source : PhysOrg
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Without plants, Earth would cook under billions of tons of additional carbon
Enhanced growth of Earth's leafy greens during the 20th century has significantly slowed the planet's transition to being red-hot, according to the first study to specify the extent to which plants have prevented climate change since pre-industrial times. Researchers based at Princeton University found that land ecosystems have kept the planet cooler by absorbing billions of tons of carbon, especially during the past 60 years. The planet's land-based carbon "sink" -- or carbon-storage capacity -- has kept 186 billion to 192 billion tons of carbon out of the atmosphere since the mid-20th century, the researchers report in the Proceedings of the National Academy of Sciences. From the 1860s to the 1950s, land use by humans was a substantial source of the carbon entering the atmosphere because of deforestation and logging. After the 1950s, however, humans began to use land differently, such as by restoring forests and adopting agriculture that, while larger scale, is higher yield. At the same time, industries and automobiles continued to steadily emit carbon dioxide that contributed to a botanical boom. Although a greenhouse gas and pollutant, carbon dioxide also is a plant nutrient.
Had Earth's terrestrial ecosystems remained a carbon source they would have instead generated 65 billion to 82 billion tons of carbon in addition to the carbon that it would not have absorbed, the researchers found. That means a total of 251 billion to 274 billion additional tons of carbon would currently be in the atmosphere. That much carbon would have pushed the atmosphere's current carbon dioxide concentration to 485 parts-per-million (ppm), the researchers report -- well past the scientifically accepted threshold of 450 (ppm) at which Earth's climate could drastically and irreversibly change. The current concentration is 400 ppm.
Those "carbon savings" amount to a current average global temperature that is cooler by one-third of a degree Celsius (or a half-degree Fahrenheit), which would have been a sizeable jump, the researchers report. The planet has warmed by only 0.74 degrees Celsius (1.3 degrees Fahrenheit) since the early 1900s, and the point at which scientists calculate the global temperature would be dangerously high is a mere 2 degrees Celsius (3.6 degrees Fahrenheit) more than pre-industrial levels.
The study is the most comprehensive look at the historical role of terrestrial ecosystems in controlling atmospheric carbon, explained first author Elena Shevliakova, a senior climate modeler in Princeton's Department of Ecology and Evolutionary Biology. Previous research has focused on how plants might offset carbon in the future, but overlooked the importance of increased vegetation uptake in the past, she said.
"People always say we know carbon sinks are important for the climate," Shevliakova said. "We actually for the first time have a number and we can say what that sink means for us now in terms of carbon savings."
"Changes in carbon dioxide emissions from land-use activities need to be carefully considered. Until recently, most studies would just take fossil-fuel emissions and land-use emissions from simple models, plug them in and not consider how managed lands such as recovering forests take up carbon," she said. "It's not just climate -- it's people. On land, people are major drivers of changes in land carbon. They're not just taking carbon out of the land, they're actually changing the land's capacity to take up carbon."
Scott Saleska, an associate professor of ecology and evolutionary biology at the University of Arizona who studies interactions between vegetation and climate, said that the researchers provide a potentially compelling argument for continued forest restoration and preservation by specifying the "climate impact" of vegetation. Saleska is familiar with the research but had no role in it.
"I think this does have implications for policies that try to value the carbon saved when you restore or preserve a forest," Saleska said. "This modeling approach could be used to state the complete 'climate impact' of preserving large forested areas, whereas most current approaches just account for the 'carbon impact.' Work like this could help forest-preservation programs more accurately consider the climate impacts of policy measures related to forest preservation."
Although the researchers saw a strong historical influence of carbon fertilization in carbon absorption, that exchange does have its limits, Saleska said. If carbon dioxide levels in the atmosphere continue rising, more vegetation would be needed to maintain the size of the carbon sink Shevliakova and her colleagues reported.
"There is surely some limit to how long increasing carbon dioxide can continue to promote plant growth that absorbs carbon dioxide," Saleska said. "Carbon dioxide is food for plants, and putting more food out there stimulates them to 'eat' more. However, just like humans, eventually they get full and putting more food out doesn't stimulate more eating."
The researchers used the comprehensive Earth System Model (ESM2G), a climate-carbon cycle model developed by the National Oceanic and Atmospheric Administration's Geophysical Fluid and Dynamics Laboratory (GFDL), to simulate how carbon and climate interacted with vegetation, soil and marine ecosystems between 1861 and 2005. The GFDL model predicted changes in climate and in atmospheric concentrations of carbon dioxide based on fossil fuel emissions of carbon. Uniquely, the model also predicted emissions from land-use changes -- such as deforestation, wood harvesting and forest regrowth -- that occurred from 1700 to 2005.
"Unless you really understand what the land-use processes are it's very hard to say what the system will do as a whole," said Shevliakova, who worked with corresponding author Stephen Pacala, Princeton's Frederick D. Petrie Professor in Ecology and Evolutionary Biology; Sergey Malyshev, a professional specialist in ecology and evolutionary biology at Princeton; GFDL physical scientists Ronald Stouffer and John Krasting; and George Hurtt, a professor of geographical sciences at the University of Maryland.
"After the 1940s and 1950s, if you look at the land-use change trajectory, it's been slowed down in the expansion of agriculture and pastures," Shevliakova said. "When you go from extensive agriculture to intensive agriculture you industrialize the production of food, so people now use fertilizers instead of chopping down more forests. A decrease in global deforestation combined with enhanced vegetation growth caused by the rapid increase in carbon dioxide changed the land from a carbon source into a carbon sink."
For scientists, the model is a significant contribution to understanding the terrestrial carbon sink, Saleska said. Scientists only uncovered the land-based carbon sink about two decades ago, while models that can combine the effects of climate change and vegetation growth have only been around for a little more than 10 years, Saleska said. There is work to be done to refine climate models and the Princeton-led research opens up new possibilities while also lending confidence to future climate projections, Saleska said.
"A unique value of this study is that it simulates the past, for which, unlike the future, we have observations," Saleska said. "Past observations about climate and carbon dioxide provide a test about how good the model simulation was. If it's right about the past, we should have more confidence in its ability to predict the future."
Source : Science News
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Perception of soft mechanical stress in Arabidopsis leaves activates disease resistance
Lehcen Benikhlef1†, Floriane L’Haridon1*†, Eliane Abou-Mansour1, Mario Serrano1, Matteo Binda1, Alex Costa2, Silke Lehmann1 and Jean-Pierre Métraux1
1. Department of Biology, University of Fribourg, 10 chemin du Musée, CH-1700, Fribourg, Switzerland
2 Department of Biosciences, University of Milan, via G. Celoria 26, 20133, Milan, Italy
Background In a previous study we have shown that wounding of Arabidopsis thaliana leaves induces a strong and transient immunity to Botrytis cinerea, the causal agent of grey mould. Reactive oxygen species (ROS) are formed within minutes after wounding and are required for wound–induced resistance to B. cinerea.
Results In this study, we have further explored ROS and resistance to B. cinerea in leaves of A. thaliana exposed to a soft form of mechanical stimulation without overt tissue damage. After gentle mechanical sweeping of leaf surfaces, a strong resistance to B. cinerea was observed. This was preceded by a rapid change in calcium concentration and a release of ROS, accompanied by changes in cuticle permeability, induction of the expression of genes typically associated with mechanical stress and release of biologically active diffusates from the surface. This reaction to soft mechanical stress (SMS) was fully independent of jasmonate (JA signaling). In addition, leaves exposed soft mechanical stress released a biologically active product capable of inducing resistance to B. cinerea in wild type control leaves.
Conclusion Arabidopsis can detect and convert gentle forms of mechanical stimulation into a strong activation of defense against the virulent fungus B. cinerea.
Source : BMC Plant Biology
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A bit touchy: Plants’ insect defenses activated by touch
Rice University study links touch-activated genes to both growth and insect defense
A new study by Rice University scientists reveals that plants can use the sense of touch to fight off fungal infections and insects. The study, which will be published in the April 24 issue of Current Biology, finds that plant defenses are enhanced when plants are touched.
“From previous studies, we knew that plants change their growth in response to touch but we didn’t know how these growth changes were activated,” said Wassim Chehab, a faculty fellow in Rice’s Department of Biochemistry and Cell Biology and lead author of the new study. “We used a widely studied plant, Arabidopsis thaliana, to test the idea that the touch-induced growth was regulated by a plant hormone called jasmonate.”
Jasmonate plays a critical role in initiating plant defenses against plant-eating insects. When jasmonate levels go up, the plant increases production of metabolites that give herbivores an upset stomach. Jasmonate defenses, which also protect against some fungal infections, are employed by virtually all plants, including tomatoes, rice and corn. The new study provides the first evidence that these defenses are triggered when plants are touched. In the study, students touched the plants in a laboratory, but the researchers say the touch-induced response could also be activated by animals, including insects, and wind.
“Plants can’t move, so it makes sense for them to have a highly developed sense of touch to react quickly to changes in their environment,” said study co-author Janet Braam, professor and chair of Rice’s Department of Biochemistry and Cell Biology.
The famed Venus flytrap uses its sense of touch to rapidly close and trap insects. But in prior research at Rice, Braam and her colleagues showed that Arabidopsis was also extremely responsive to touch. In 2000, her lab used tools of biotechnology to produce a plant that glowed with light wherever it was touched. They also showed that Arabidopsis plants that were touched regularly grew much shorter and slower — much like trees exposed to a windy coastline will grow short and bent.
“In this new work, we show that jasmonate mediates this growth response in Arabidopsis,” Braam said. “Our experiments show that plants that are repeatedly touched maintain high levels of jasmonate and therefore have enhanced insect and fungal tolerance. In addition, we found that eliminating key genes required for jasmonate production results in the inability of plants to grow shorter and slower when touched.”
Braam and Chehab also found that plants that were touched often, and consequently had high levels of jasmonate, were more resistant to fungal and insect attacks.
Chehab said plants do not base their production of jasmonate on a single source of information.
“There are multiple signals that can influence the jasmonate response,” Chehab said. “Touch is one, but we also recently found that this response can be mediated by the plant’s internal clock, or circadian rhythm. It’s a complicated picture, but by piecing it together, we get a clearer understanding of plant pest resistance.”
Source : Rice University
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Tree and human health may be linked
Evidence is increasing from multiple scientific fields that exposure to the natural environment can improve human health. In a new study by the U.S. Forest Service, the presence of trees was associated with human health.
For Geoffrey Donovan, a research forester at the Forest Service's Pacific Northwest Research Station, and his colleagues, the loss of 100 million trees in the eastern and midwestern United States was an unprecedented opportunity to study the impact of a major change in the natural environment on human health.
In an analysis of 18 years of data from 1,296 counties in 15 states, researchers found that Americans living in areas infested by the emerald ash borer, a beetle that kills ash trees, suffered from an additional 15,000 deaths from cardiovascular disease and 6,000 more deaths from lower respiratory disease when compared to uninfected areas. When emerald ash borer comes into a community, city streets lined with ash trees become treeless.
The researchers analyzed demographic, human mortality, and forest health data at the county level between 1990 and 2007. The data came from counties in states with at least one confirmed case of the emerald ash borer in 2010. The findings -- which hold true after accounting for the influence of demographic differences, like income, race, and education -- are published in the current issue of the American Journal of Preventive Medicine.
"There's a natural tendency to see our findings and conclude that, surely, the higher mortality rates are because of some confounding variable, like income or education, and not the loss of trees," said Donovan. "But we saw the same pattern repeated over and over in counties with very different demographic makeups."
Although the study shows the association between loss of trees and human mortality from cardiovascular and lower respiratory disease, it did not prove a causal link. The reason for the association is yet to be determined.
The emerald ash borer was first discovered near Detroit, Michigan, in 2002. The borer attacks all 22 species of North American ash and kills virtually all of the trees it infests.
Source : Science Daily
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The Intelligent Plant
Scientists debate a new way of understanding flora.
by Michael Pollan
In 1973, a book claiming that plants were sentient beings that feel emotions, prefer classical music to rock and roll, and can respond to the unspoken thoughts of humans hundreds of miles away landed on the New York Times best-seller list for nonfiction. “The Secret Life of Plants,” by Peter Tompkins and Christopher Bird, presented a beguiling mashup of legitimate plant science, quack experiments, and mystical nature worship that captured the public imagination at a time when New Age thinking was seeping into the mainstream. The most memorable passages described the experiments of a former C.I.A. polygraph expert named Cleve Backster, who, in 1966, on a whim, hooked up a galvanometer to the leaf of a dracaena, a houseplant that he kept in his office. To his astonishment, Backster found that simply by imagining the dracaena being set on fire he could make it rouse the needle of the polygraph machine, registering a surge of electrical activity suggesting that the plant felt stress. “Could the plant have been reading his mind?” the authors ask. “Backster felt like running into the street and shouting to the world, ‘Plants can think!’ ”
Backster and his collaborators went on to hook up polygraph machines to dozens of plants, including lettuces, onions, oranges, and bananas. He claimed that plants reacted to the thoughts (good or ill) of humans in close proximity and, in the case of humans familiar to them, over a great distance. In one experiment designed to test plant memory, Backster found that a plant that had witnessed the murder (by stomping) of another plant could pick out the killer from a lineup of six suspects, registering a surge of electrical activity when the murderer was brought before it. Backster’s plants also displayed a strong aversion to interspecies violence. Some had a stressful response when an egg was cracked in their presence, or when live shrimp were dropped into boiling water, an experiment that Backster wrote up for the International Journal of Parapsychology, in 1968. In the ensuing years, several legitimate plant scientists tried to reproduce the “Backster effect” without success. Much of the science in “The Secret Life of Plants” has been discredited. But the book had made its mark on the culture. Americans began talking to their plants and playing Mozart for them, and no doubt many still do. This might seem harmless enough; there will probably always be a strain of romanticism running through our thinking about plants. (Luther Burbank and George Washington Carver both reputedly talked to, and listened to, the plants they did such brilliant work with.) But in the view of many plant scientists “The Secret Life of Plants” has done lasting damage to their field. According to Daniel Chamovitz, an Israeli biologist who is the author of the recent book “What a Plant Knows,” Tompkins and Bird “stymied important research on plant behavior as scientists became wary of any studies that hinted at parallels between animal senses and plant senses.” Others contend that “The Secret Life of Plants” led to “self-censorship” among researchers seeking to explore the “possible homologies between neurobiology and phytobiology”; that is, the possibility that plants are much more intelligent and much more like us than most people think—capable of cognition, communication, information processing, computation, learning, and memory.
The quotation about self-censorship appeared in a controversial 2006 article in Trends in Plant Science proposing a new field of inquiry that the authors, perhaps somewhat recklessly, elected to call “plant neurobiology.” The six authors—among them Eric D. Brenner, an American plant molecular biologist; Stefano Mancuso, an Italian plant physiologist; František Baluška, a Slovak cell biologist; and Elizabeth Van Volkenburgh, an American plant biologist—argued that the sophisticated behaviors observed in plants cannot at present be completely explained by familiar genetic and biochemical mechanisms. Plants are able to sense and optimally respond to so many environmental variables—light, water, gravity, temperature, soil structure, nutrients, toxins, microbes, herbivores, chemical signals from other plants—that there may exist some brainlike information-processing system to integrate the data and coördinate a plant’s behavioral response. The authors pointed out that electrical and chemical signalling systems have been identified in plants which are homologous to those found in the nervous systems of animals. They also noted that neurotransmitters such as serotonin, dopamine, and glutamate have been found in plants, though their role remains unclear.
Hence the need for plant neurobiology, a new field “aimed at understanding how plants perceive their circumstances and respond to environmental input in an integrated fashion.” The article argued that plants exhibit intelligence, defined by the authors as “an intrinsic ability to process information from both abiotic and biotic stimuli that allows optimal decisions about future activities in a given environment.” Shortly before the article’s publication, the Society for Plant Neurobiology held its first meeting, in Florence, in 2005. A new scientific journal, with the less tendentious title Plant Signaling & Behavior, appeared the following year.
Depending on whom you talk to in the plant sciences today, the field of plant neurobiology represents either a radical new paradigm in our understanding of life or a slide back down into the murky scientific waters last stirred up by “The Secret Life of Plants.” Its proponents believe that we must stop regarding plants as passive objects—the mute, immobile furniture of our world—and begin to treat them as protagonists in their own dramas, highly skilled in the ways of contending in nature. They would challenge contemporary biology’s reductive focus on cells and genes and return our attention to the organism and its behavior in the environment. It is only human arrogance, and the fact that the lives of plants unfold in what amounts to a much slower dimension of time, that keep us from appreciating their intelligence and consequent success. Plants dominate every terrestrial environment, composing ninety-nine per cent of the biomass on earth. By comparison, humans and all the other animals are, in the words of one plant neurobiologist, “just traces.”
Many plant scientists have pushed back hard against the nascent field, beginning with a tart, dismissive letter in response to the Brenner manifesto, signed by thirty-six prominent plant scientists (Alpi et al., in the literature) and published in Trends in Plant Science. “We begin by stating simply that there is no evidence for structures such as neurons, synapses or a brain in plants,” the authors wrote. No such claim had actually been made—the manifesto had spoken only of “homologous” structures—but the use of the word “neurobiology” in the absence of actual neurons was apparently more than many scientists could bear.
“Yes, plants have both short- and long-term electrical signalling, and they use some neurotransmitter-like chemicals as chemical signals,” Lincoln Taiz, an emeritus professor of plant physiology at U.C. Santa Cruz and one of the signers of the Alpi letter, told me. “But the mechanisms are quite different from those of true nervous systems.” Taiz says that the writings of the plant neurobiologists suffer from “over-interpretation of data, teleology, anthropomorphizing, philosophizing, and wild speculations.” He is confident that eventually the plant behaviors we can’t yet account for will be explained by the action of chemical or electrical pathways, without recourse to “animism.” Clifford Slayman, a professor of cellular and molecular physiology at Yale, who also signed the Alpi letter (and who helped discredit Tompkins and Bird), was even more blunt. “ ‘Plant intelligence’ is a foolish distraction, not a new paradigm,” he wrote in a recent e-mail. Slayman has referred to the Alpi letter as “the last serious confrontation between the scientific community and the nuthouse on these issues.” Scientists seldom use such language when talking about their colleagues to a journalist, but this issue generates strong feelings, perhaps because it smudges the sharp line separating the animal kingdom from the plant kingdom. The controversy is less about the remarkable discoveries of recent plant science than about how to interpret and name them: whether behaviors observed in plants which look very much like learning, memory, decision-making, and intelligence deserve to be called by those terms or whether those words should be reserved exclusively for creatures with brains.
No one I spoke to in the loose, interdisciplinary group of scientists working on plant intelligence claims that plants have telekinetic powers or feel emotions. Nor does anyone believe that we will locate a walnut-shaped organ somewhere in plants which processes sensory data and directs plant behavior. More likely, in the scientists’ view, intelligence in plants resembles that exhibited in insect colonies, where it is thought to be an emergent property of a great many mindless individuals organized in a network. Much of the research on plant intelligence has been inspired by the new science of networks, distributed computing, and swarm behavior, which has demonstrated some of the ways in which remarkably brainy behavior can emerge in the absence of actual brains.
“If you are a plant, having a brain is not an advantage,” Stefano Mancuso points out. Mancuso is perhaps the field’s most impassioned spokesman for the plant point of view. A slight, bearded Calabrian in his late forties, he comes across more like a humanities professor than like a scientist. When I visited him earlier this year at the International Laboratory of Plant Neurobiology, at the University of Florence, he told me that his conviction that humans grossly underestimate plants has its origins in a science-fiction story he remembers reading as a teen-ager. A race of aliens living in a radically sped-up dimension of time arrive on Earth and, unable to detect any movement in humans, come to the logical conclusion that we are “inert material” with which they may do as they please. The aliens proceed ruthlessly to exploit us. (Mancuso subsequently wrote to say that the story he recounted was actually a mangled recollection of an early “Star Trek” episode called “Wink of an Eye.”)
In Mancuso’s view, our “fetishization” of neurons, as well as our tendency to equate behavior with mobility, keeps us from appreciating what plants can do. For instance, since plants can’t run away and frequently get eaten, it serves them well not to have any irreplaceable organs. “A plant has a modular design, so it can lose up to ninety per cent of its body without being killed,” he said. “There’s nothing like that in the animal world. It creates a resilience.”
Indeed, many of the most impressive capabilities of plants can be traced to their unique existential predicament as beings rooted to the ground and therefore unable to pick up and move when they need something or when conditions turn unfavorable. The “sessile life style,” as plant biologists term it, calls for an extensive and nuanced understanding of one’s immediate environment, since the plant has to find everything it needs, and has to defend itself, while remaining fixed in place. A highly developed sensory apparatus is required to locate food and identify threats. Plants have evolved between fifteen and twenty distinct senses, including analogues of our five: smell and taste (they sense and respond to chemicals in the air or on their bodies); sight (they react differently to various wavelengths of light as well as to shadow); touch (a vine or a root “knows” when it encounters a solid object); and, it has been discovered, sound. In a recent experiment, Heidi Appel, a chemical ecologist at the University of Missouri, found that, when she played a recording of a caterpillar chomping a leaf for a plant that hadn’t been touched, the sound primed the plant’s genetic machinery to produce defense chemicals. Another experiment, done in Mancuso’s lab and not yet published, found that plant roots would seek out a buried pipe through which water was flowing even if the exterior of the pipe was dry, which suggested that plants somehow “hear” the sound of flowing water.
The sensory capabilities of plant roots fascinated Charles Darwin, who in his later years became increasingly passionate about plants; he and his son Francis performed scores of ingenious experiments on plants. Many involved the root, or radicle, of young plants, which the Darwins demonstrated could sense light, moisture, gravity, pressure, and several other environmental qualities, and then determine the optimal trajectory for the root’s growth. The last sentence of Darwin’s 1880 book, “The Power of Movement in Plants,” has assumed scriptural authority for some plant neurobiologists: “It is hardly an exaggeration to say that the tip of the radicle . . . having the power of directing the movements of the adjoining parts, acts like the brain of one of the lower animals; the brain being seated within the anterior end of the body, receiving impressions from the sense organs and directing the several movements.” Darwin was asking us to think of the plant as a kind of upside-down animal, with its main sensory organs and “brain” on the bottom, underground, and its sexual organs on top.
Scientists have since found that the tips of plant roots, in addition to sensing gravity, moisture, light, pressure, and hardness, can also sense volume, nitrogen, phosphorus, salt, various toxins, microbes, and chemical signals from neighboring plants. Roots about to encounter an impenetrable obstacle or a toxic substance change course before they make contact with it. Roots can tell whether nearby roots are self or other and, if other, kin or stranger. Normally, plants compete for root space with strangers, but, when researchers put four closely related Great Lakes sea-rocket plants (Cakile edentula) in the same pot, the plants restrained their usual competitive behaviors and shared resources.
Somehow, a plant gathers and integrates all this information about its environment, and then “decides”—some scientists deploy the quotation marks, indicating metaphor at work; others drop them—in precisely what direction to deploy its roots or its leaves. Once the definition of “behavior” expands to include such things as a shift in the trajectory of a root, a reallocation of resources, or the emission of a powerful chemical, plants begin to look like much more active agents, responding to environmental cues in ways more subtle or adaptive than the word “instinct” would suggest. “Plants perceive competitors and grow away from them,” Rick Karban, a plant ecologist at U.C. Davis, explained, when I asked him for an example of plant decision-making. “They are more leery of actual vegetation than they are of inanimate objects, and they respond to potential competitors before actually being shaded by them.” These are sophisticated behaviors, but, like most plant behaviors, to an animal they’re either invisible or really, really slow.
The sessile life style also helps account for plants’ extraordinary gift for biochemistry, which far exceeds that of animals and, arguably, of human chemists. (Many drugs, from aspirin to opiates, derive from compounds designed by plants.) Unable to run away, plants deploy a complex molecular vocabulary to signal distress, deter or poison enemies, and recruit animals to perform various services for them. A recent study in Science found that the caffeine produced by many plants may function not only as a defense chemical, as had previously been thought, but in some cases as a psychoactive drug in their nectar. The caffeine encourages bees to remember a particular plant and return to it, making them more faithful and effective pollinators.
One of the most productive areas of plant research in recent years has been plant signalling. Since the early nineteen-eighties, it has been known that when a plant’s leaves are infected or chewed by insects they emit volatile chemicals that signal other leaves to mount a defense. Sometimes this warning signal contains information about the identity of the insect, gleaned from the taste of its saliva. Depending on the plant and the attacker, the defense might involve altering the leaf’s flavor or texture, or producing toxins or other compounds that render the plant’s flesh less digestible to herbivores. When antelopes browse acacia trees, the leaves produce tannins that make them unappetizing and difficult to digest. When food is scarce and acacias are overbrowsed, it has been reported, the trees produce sufficient amounts of toxin to kill the animals.
Perhaps the cleverest instance of plant signalling involves two insect species, the first in the role of pest and the second as its exterminator. Several species, including corn and lima beans, emit a chemical distress call when attacked by caterpillars. Parasitic wasps some distance away lock in on that scent, follow it to the afflicted plant, and proceed to slowly destroy the caterpillars. Scientists call these insects “plant bodyguards.”
Plants speak in a chemical vocabulary we can’t directly perceive or comprehend. The first important discoveries in plant communication were made in the lab in the nineteen-eighties, by isolating plants and their chemical emissions in Plexiglas chambers, but Rick Karban, the U.C. Davis ecologist, and others have set themselves the messier task of studying how plants exchange chemical signals outdoors, in a natural setting. Recently, I visited Karban’s study plot at the University of California’s Sagehen Creek Field Station, a few miles outside Truckee. On a sun-flooded hillside high in the Sierras, he introduced me to the ninety-nine sagebrush plants—low, slow-growing gray-green shrubs marked with plastic flags—that he and his colleagues have kept under close surveillance for more than a decade.
Karban, a fifty-nine-year-old former New Yorker, is slender, with a thatch of white curls barely contained by a floppy hat. He has shown that when sagebrush leaves are clipped in the spring—simulating an insect attack that triggers the release of volatile chemicals—both the clipped plant and its unclipped neighbors suffer significantly less insect damage over the season. Karban believes that the plant is alerting all its leaves to the presence of a pest, but its neighbors pick up the signal, too, and gird themselves against attack. “We think the sagebrush are basically eavesdropping on one another,” Karban said. He found that the more closely related the plants the more likely they are to respond to the chemical signal, suggesting that plants may display a form of kin recognition. Helping out your relatives is a good way to improve the odds that your genes will survive.
The field work and data collection that go into making these discoveries are painstaking in the extreme. At the bottom of a meadow raked by the slanted light of late summer, two collaborators from Japan, Kaori Shiojiri and Satomi Ishizaki, worked in the shade of a small pine, squatting over branches of sagebrush that Karban had tagged and cut. Using clickers, they counted every trident-shaped leaf on every branch, and then counted and recorded every instance of leaf damage, one column for insect bites, another for disease. At the top of the meadow, another collaborator, James Blande, a chemical ecologist from England, tied plastic bags around sagebrush stems and inflated the bags with filtered air. After waiting twenty minutes for the leaves to emit their volatiles, he pumped the air through a metal cylinder containing an absorbent material that collected the chemical emissions. At the lab, a gas chromatograph-mass spectrometer would yield a list of the compounds collected—more than a hundred in all. Blande offered to let me put my nose in one of the bags; the air was powerfully aromatic, with a scent closer to aftershave than to perfume. Gazing across the meadow of sagebrush, I found it difficult to imagine the invisible chemical chatter, including the calls of distress, going on all around—or that these motionless plants were engaged in any kind of “behavior” at all.
Research on plant communication may someday benefit farmers and their crops. Plant-distress chemicals could be used to prime plant defenses, reducing the need for pesticides. Jack Schultz, a chemical ecologist at the University of Missouri, who did some of the pioneering work on plant signalling in the early nineteen-eighties, is helping to develop a mechanical “nose” that, attached to a tractor and driven through a field, could help farmers identify plants under insect attack, allowing them to spray pesticides only when and where they are needed.
Karban told me that, in the nineteen-eighties, people working on plant communication faced some of the same outrage that scientists working on plant intelligence (a term he cautiously accepts) do today. “This stuff has been enormously contentious,” he says, referring to the early days of research into plant communication, work that is now generally accepted. “It took me years to get some of these papers published. People would literally be screaming at one another at scientific meetings.” He added, “Plant scientists in general are incredibly conservative. We all think we want to hear novel ideas, but we don’t, not really.”
I first met Karban at a scientific meeting in Vancouver last July, when he presented a paper titled “Plant Communication and Kin Recognition in Sagebrush.” The meeting would have been the sixth gathering of the Society for Plant Neurobiology, if not for the fact that, under pressure from certain quarters of the scientific establishment, the group’s name had been changed four years earlier to the less provocative Society for Plant Signaling and Behavior. The plant biologist Elizabeth Van Volkenburgh, of the University of Washington, who was one of the founders of the society, told me that the name had been changed after a lively internal debate; she felt that jettisoning “neurobiology” was probably for the best. “I was told by someone at the National Science Foundation that the N.S.F. would never fund anything with the words ‘plant neurobiology’ in it. He said, and I quote, ‘ “Neuro” belongs to animals.’ ” (An N.S.F. spokesperson said that, while the society is not eligible for funding by the foundation’s neurobiology program, “the N.S.F. does not have a boycott of any sort against the society.”) Two of the society’s co-founders, Stefano Mancuso and František Baluška, argued strenuously against the name change, and continue to use the term “plant neurobiology” in their own work and in the names of their labs.
The meeting consisted of three days of PowerPoint presentations delivered in a large, modern lecture hall at the University of British Columbia before a hundred or so scientists. Most of the papers were highly technical presentations on plant signalling—the kind of incremental science that takes place comfortably within the confines of an established scientific paradigm, which plant signalling has become. But a handful of speakers presented work very much within the new paradigm of plant intelligence, and they elicited strong reactions.
The most controversial presentation was “Animal-Like Learning in Mimosa Pudica,” an unpublished paper by Monica Gagliano, a thirty-seven-year-old animal ecologist at the University of Western Australia who was working in Mancuso’s lab in Florence. Gagliano, who is tall, with long brown hair parted in the middle, based her experiment on a set of protocols commonly used to test learning in animals. She focussed on an elementary type of learning called “habituation,” in which an experimental subject is taught to ignore an irrelevant stimulus. “Habituation enables an organism to focus on the important information, while filtering out the rubbish,” Gagliano explained to the audience of plant scientists. How long does it take the animal to recognize that a stimulus is “rubbish,” and then how long will it remember what it has learned? Gagliano’s experimental question was bracing: Could the same thing be done with a plant?
Mimosa pudica, also called the “sensitive plant,” is that rare plant species with a behavior so speedy and visible that animals can observe it; the Venus flytrap is another. When the fernlike leaves of the mimosa are touched, they instantly fold up, presumably to frighten insects. The mimosa also collapses its leaves when the plant is dropped or jostled. Gagliano potted fifty-six mimosa plants and rigged a system to drop them from a height of fifteen centimetres every five seconds. Each “training session” involved sixty drops. She reported that some of the mimosas started to reopen their leaves after just four, five, or six drops, as if they had concluded that the stimulus could be safely ignored. “By the end, they were completely open,” Gagliano said to the audience. “They couldn’t care less anymore.”
Was it just fatigue? Apparently not: when the plants were shaken, they again closed up. “ ‘Oh, this is something new,’ ” Gagliano said, imagining these events from the plants’ point of view. “You see, you want to be attuned to something new coming in. Then we went back to the drops, and they didn’t respond.” Gagliano reported that she retested her plants after a week and found that they continued to disregard the drop stimulus, indicating that they “remembered” what they had learned. Even after twenty-eight days, the lesson had not been forgotten. She reminded her colleagues that, in similar experiments with bees, the insects forgot what they had learned after just forty-eight hours. Gagliano concluded by suggesting that “brains and neurons are a sophisticated solution but not a necessary requirement for learning,” and that there is “some unifying mechanism across living systems that can process information and learn.”
A lively exchange followed. Someone objected that dropping a plant was not a relevant trigger, since that doesn’t happen in nature. Gagliano pointed out that electric shock, an equally artificial trigger, is often used in animal-learning experiments. Another scientist suggested that perhaps her plants were not habituated, just tuckered out. She argued that twenty-eight days would be plenty of time to rebuild their energy reserves.
On my way out of the lecture hall, I bumped into Fred Sack, a prominent botanist at the University of British Columbia. I asked him what he thought of Gagliano’s presentation. “Bullshit,” he replied. He explained that the word “learning” implied a brain and should be reserved for animals: “Animals can exhibit learning, but plants evolve adaptations.” He was making a distinction between behavioral changes that occur within the lifetime of an organism and those which arise across generations. At lunch, I sat with a Russian scientist, who was equally dismissive. “It’s not learning,” he said. “So there’s nothing to discuss.”
Later that afternoon, Gagliano seemed both stung by some of the reactions to her presentation and defiant. Adaptation is far too slow a process to explain the behavior she had observed, she told me. “How can they be adapted to something they have never experienced in their real world?” She noted that some of her plants learned faster than others, evidence that “this is not an innate or programmed response.” Many of the scientists in her audience were just getting used to the ideas of plant “behavior” and “memory” (terms that even Fred Sack said he was willing to accept); using words like “learning” and “intelligence” in plants struck them, in Sack’s words, as “inappropriate” and “just weird.” When I described the experiment to Lincoln Taiz, he suggested the words “habituation” or “desensitization” would be more appropriate than “learning.” Gagliano said that her mimosa paper had been rejected by ten journals: “None of the reviewers had problems with the data.” Instead, they balked at the language she used to describe the data. But she didn’t want to change it. “Unless we use the same language to describe the same behavior”—exhibited by plants and animals—“we can’t compare it,” she said.
Rick Karban consoled Gagliano after her talk. “I went through the same thing, just getting totally hammered,” he told her. “But you’re doing good work. The system is just not ready.” When I asked him what he thought of Gagliano’s paper, he said, “I don’t know if she’s got everything nailed down, but it’s a very cool idea that deserves to get out there and be discussed. I hope she doesn’t get discouraged.”
Scientists are often uncomfortable talking about the role of metaphor and imagination in their work, yet scientific progress often depends on both. “Metaphors help stimulate the investigative imagination of good scientists,” the British plant scientist Anthony Trewavas wrote in a spirited response to the Alpi letter denouncing plant neurobiology. “Plant neurobiology” is obviously a metaphor—plants don’t possess the type of excitable, communicative cells we call neurons. Yet the introduction of the term has raised a series of questions and inspired a set of experiments that promise to deepen our understanding not only of plants but potentially also of brains. If there are other ways of processing information, other kinds of cells and cell networks that can somehow give rise to intelligent behavior, then we may be more inclined to ask, with Mancuso, “What’s so special about neurons?”
Mancuso is the poet-philosopher of the movement, determined to win for plants the recognition they deserve and, perhaps, bring humans down a peg in the process. His somewhat grandly named International Laboratory of Plant Neurobiology, a few miles outside Florence, occupies a modest suite of labs and offices in a low-slung modern building. Here a handful of collaborators and graduate students work on the experiments Mancuso devises to test the intelligence of plants. Giving a tour of the labs, he showed me maize plants, grown under lights, that were being taught to ignore shadows; a poplar sapling hooked up to a galvanometer to measure its response to air pollution; and a chamber in which a PTR-TOF machine—an advanced kind of mass spectrometer—continuously read all the volatiles emitted by a succession of plants, from poplars and tobacco plants to peppers and olive trees. “We are making a dictionary of each species’ entire chemical vocabulary,” he explained. He estimates that a plant has three thousand chemicals in its vocabulary, while, he said with a smile, “the average student has only seven hundred words.”
Mancuso is fiercely devoted to plants—a scientist needs to “love” his subject in order to do it justice, he says. He is also gentle and unassuming, even when what he is saying is outrageous. In the corner of his office sits a forlorn Ficus benjamina, or weeping fig, and on the walls are photographs of Mancuso in an astronaut’s jumpsuit floating in the cabin of a zero-gravity aircraft; he has collaborated with the European Space Agency, which has supported his research on plant behavior in micro- and hyper-gravity. (One of his experiments was carried on board the last flight of the space shuttle Endeavor, in May of 2011.) A decade ago, Mancuso persuaded a Florentine bank foundation to underwrite much of his research and help launch the Society for Plant Neurobiology; his lab also receives grants from the European Union.
Early in our conversation, I asked Mancuso for his definition of “intelligence.” Spending so much time with the plant neurobiologists, I could feel my grasp on the word getting less sure. It turns out that I am not alone: philosophers and psychologists have been arguing over the definition of intelligence for at least a century, and whatever consensus there may once have been has been rapidly slipping away. Most definitions of intelligence fall into one of two categories. The first is worded so that intelligence requires a brain; the definition refers to intrinsic mental qualities such as reason, judgment, and abstract thought. The second category, less brain-bound and metaphysical, stresses behavior, defining intelligence as the ability to respond in optimal ways to the challenges presented by one’s environment and circumstances. Not surprisingly, the plant neurobiologists jump into this second camp.
“I define it very simply,” Mancuso said. “Intelligence is the ability to solve problems.” In place of a brain, “what I am looking for is a distributed sort of intelligence, as we see in the swarming of birds.” In a flock, each bird has only to follow a few simple rules, such as maintaining a prescribed distance from its neighbor, yet the collective effect of a great many birds executing a simple algorithm is a complex and supremely well-coördinated behavior. Mancuso’s hypothesis is that something similar is at work in plants, with their thousands of root tips playing the role of the individual birds—gathering and assessing data from the environment and responding in local but coördinated ways that benefit the entire organism.
“Neurons perhaps are overrated,” Mancuso said. “They’re really just excitable cells.” Plants have their own excitable cells, many of them in a region just behind the root tip. Here Mancuso and his frequent collaborator, František Baluška, have detected unusually high levels of electrical activity and oxygen consumption. They’ve hypothesized in a series of papers that this so-called “transition zone” may be the locus of the “root brain” first proposed by Darwin. The idea remains unproved and controversial. “What’s going on there is not well understood,” Lincoln Taiz told me, “but there is no evidence it is a command center.”
How plants do what they do without a brain—what Anthony Trewavas has called their “mindless mastery”—raises questions about how our brains do what they do. When I asked Mancuso about the function and location of memory in plants, he speculated about the possible role of calcium channels and other mechanisms, but then he reminded me that mystery still surrounds where and how our memories are stored: “It could be the same kind of machinery, and figuring it out in plants may help us figure it out in humans.”
The hypothesis that intelligent behavior in plants may be an emergent property of cells exchanging signals in a network might sound far-fetched, yet the way that intelligence emerges from a network of neurons may not be very different. Most neuroscientists would agree that, while brains considered as a whole function as centralized command centers for most animals, within the brain there doesn’t appear to be any command post; rather, one finds a leaderless network. That sense we get when we think about what might govern a plant—that there is no there there, no wizard behind the curtain pulling the levers—may apply equally well to our brains.
In Martin Amis’s 1995 novel, “The Information,” we meet a character who aspires to write “The History of Increasing Humiliation,” a treatise chronicling the gradual dethronement of humankind from its position at the center of the universe, beginning with Copernicus. “Every century we get smaller,” Amis writes. Next came Darwin, who brought the humbling news that we are the product of the same natural laws that created animals. In the last century, the formerly sharp lines separating humans from animals—our monopolies on language, reason, toolmaking, culture, even self-consciousness—have been blurred, one after another, as science has granted these capabilities to other animals.
Mancuso and his colleagues are writing the next chapter in “The History of Increasing Humiliation.” Their project entails breaking down the walls between the kingdoms of plants and animals, and it is proceeding not only experiment by experiment but also word by word. Start with that slippery word “intelligence.” Particularly when there is no dominant definition (and when measurements of intelligence, such as I.Q., have been shown to be culturally biased), it is possible to define intelligence in a way that either reinforces the boundary between animals and plants (say, one that entails abstract thought) or undermines it. Plant neurobiologists have chosen to define intelligence democratically, as an ability to solve problems or, more precisely, to respond adaptively to circumstances, including ones unforeseen in the genome.
“I agree that humans are special,” Mancuso says. “We are the first species able to argue about what intelligence is. But it’s the quantity, not the quality” of intelligence that sets us apart. We exist on a continuum with the acacia, the radish, and the bacterium. “Intelligence is a property of life,” he says. I asked him why he thinks people have an easier time granting intelligence to computers than to plants. (Fred Sack told me that he can abide the term “artificial intelligence,” because the intelligence in this case is modified by the word “artificial,” but not “plant intelligence.” He offered no argument, except to say, “I’m in the majority in saying it’s a little weird.”) Mancuso thinks we’re willing to accept artificial intelligence because computers are our creations, and so reflect our own intelligence back at us. They are also our dependents, unlike plants: “If we were to vanish tomorrow, the plants would be fine, but if the plants vanished . . .” Our dependence on plants breeds a contempt for them, Mancuso believes. In his somewhat topsy-turvy view, plants “remind us of our weakness.”
“Memory” may be an even thornier word to apply across kingdoms, perhaps because we know so little about how it works. We tend to think of memories as immaterial, but in animal brains some forms of memory involve the laying down of new connections in a network of neurons. Yet there are ways to store information biologically that don’t require neurons. Immune cells “remember” their experience of pathogens, and call on that memory in subsequent encounters. In plants, it has long been known that experiences such as stress can alter the molecular wrapping around the chromosomes; this, in turn, determines which genes will be silenced and which expressed. This so-called “epigenetic” effect can persist and sometimes be passed down to offspring. More recently, scientists have found that life events such as trauma or starvation produce epigenetic changes in animal brains (coding for high levels of cortisol, for example) that are long-lasting and can also be passed down to offspring, a form of memory much like that observed in plants.
While talking with Mancuso, I kept thinking about words like “will,” “choice,” and “intention,” which he seemed to attribute to plants rather casually, almost as if they were acting consciously. At one point, he told me about the dodder vine, Cuscuta europaea, a parasitic white vine that winds itself around the stalk of another plant and sucks nourishment from it. A dodder vine will “choose” among several potential hosts, assessing, by scent, which offers the best potential nourishment. Having selected a target, the vine then performs a kind of cost-benefit calculation before deciding exactly how many coils it should invest—the more nutrients in the victim, the more coils it deploys. I asked Mancuso whether he was being literal or metaphorical in attributing intention to plants.
“Here, I’ll show you something,” he said. “Then you tell me if plants have intention.” He swivelled his computer monitor around and clicked open a video.
Time-lapse photography is perhaps the best tool we have to bridge the chasm between the time scale at which plants live and our own. This example was of a young bean plant, shot in the lab over two days, one frame every ten minutes. A metal pole on a dolly stands a couple of feet away. The bean plant is “looking” for something to climb. Each spring, I witness the same process in my garden, in real time. I always assumed that the bean plants simply grow this way or that, until they eventually bump into something suitable to climb. But Mancuso’s video seems to show that this bean plant “knows” exactly where the metal pole is long before it makes contact with it. Mancuso speculates that the plant could be employing a form of echolocation. There is some evidence that plants make low clicking sounds as their cells elongate; it’s possible that they can sense the reflection of those sound waves bouncing off the metal pole.
The bean plant wastes no time or energy “looking”—that is, growing—anywhere but in the direction of the pole. And it is striving (there is no other word for it) to get there: reaching, stretching, throwing itself over and over like a fly rod, extending itself a few more inches with every cast, as it attempts to wrap its curling tip around the pole. As soon as contact is made, the plant appears to relax; its clenched leaves begin to flutter mildly. All this may be nothing more than an illusion of time-lapse photography. Yet to watch the video is to feel, momentarily, like one of the aliens in Mancuso’s formative science-fiction story, shown a window onto a dimension of time in which these formerly inert beings come astonishingly to life, seemingly conscious individuals with intentions.
In October, I loaded the bean video onto my laptop and drove down to Santa Cruz to play it for Lincoln Taiz. He began by questioning its value as scientific data: “Maybe he has ten other videos where the bean didn’t do that. You can’t take one interesting variation and generalize from it.” The bean’s behavior was, in other words, an anecdote, not a phenomenon. Taiz also pointed out that the bean in the video was leaning toward the pole in the first frame. Mancuso then sent me another video with two perfectly upright bean plants that exhibited very similar behavior. Taiz was now intrigued. “If he sees that effect consistently, it would be exciting,” he said—but it would not necessarily be evidence of plant intention. “If the phenomenon is real, it would be classified as a tropism,” such as the mechanism that causes plants to bend toward light. In this case, the stimulus remains unknown, but tropisms “do not require one to postulate either intentionality or ‘brainlike’ conceptualization,” Taiz said. “The burden of proof for the latter interpretation would clearly be on Stefano.”
Perhaps the most troublesome and troubling word of all in thinking about plants is “consciousness.” If consciousness is defined as inward awareness of oneself experiencing reality—“the feeling of what happens,” in the words of the neuroscientist Antonio Damasio—then we can (probably) safely conclude that plants don’t possess it. But if we define the term simply as the state of being awake and aware of one’s environment—“online,” as the neuroscientists say—then plants may qualify as conscious beings, at least according to Mancuso and Baluška. “The bean knows exactly what is in the environment around it,” Mancuso said. “We don’t know how. But this is one of the features of consciousness: You know your position in the world. A stone does not.”
In support of their contention that plants are conscious of their environment, Mancuso and Baluška point out that plants can be rendered unconscious by the same anesthetics that put animals out: drugs can induce in plants an unresponsive state resembling sleep. (A snoozing Venus flytrap won’t notice an insect crossing its threshold.) What’s more, when plants are injured or stressed, they produce a chemical—ethylene—that works as an anesthetic on animals. When I learned this startling fact from Baluška in Vancouver, I asked him, gingerly, if he meant to suggest that plants could feel pain. Baluška, who has a gruff mien and a large bullet-shaped head, raised one eyebrow and shot me a look that I took to mean he deemed my question impertinent or absurd. But apparently not.
“If plants are conscious, then, yes, they should feel pain,” he said. “If you don’t feel pain, you ignore danger and you don’t survive. Pain is adaptive.” I must have shown some alarm. “That’s a scary idea,” he acknowledged with a shrug. “We live in a world where we must eat other organisms.” Unprepared to consider the ethical implications of plant intelligence, I could feel my resistance to the whole idea stiffen. Descartes, who believed that only humans possessed self-consciousness, was unable to credit the idea that other animals could suffer from pain. So he dismissed their screams and howls as mere reflexes, as meaningless physiological noise. Could it be remotely possible that we are now making the same mistake with plants? That the perfume of jasmine or basil, or the scent of freshly mowed grass, so sweet to us, is (as the ecologist Jack Schultz likes to say) the chemical equivalent of a scream? Or have we, merely by posing such a question, fallen back into the muddied waters of “The Secret Life of Plants”?
Lincoln Taiz has little patience for the notion of plant pain, questioning what, in the absence of a brain, would be doing the feeling. He puts it succinctly: “No brain, no pain.” Mancuso is more circumspect. We can never determine with certainty whether plants feel pain or whether their perception of injury is sufficiently like that of animals to be called by the same word. (He and Baluška are careful to write of “plant-specific pain perception.”) “We just don’t know, so we must be silent.”
Mancuso believes that, because plants are sensitive and intelligent beings, we are obliged to treat them with some degree of respect. That means protecting their habitats from destruction and avoiding practices such as genetic manipulation, growing plants in monocultures, and training them in bonsai. But it does not prevent us from eating them. “Plants evolved to be eaten—it is part of their evolutionary strategy,” he said. He cited their modular structure and lack of irreplaceable organs in support of this view.
The central issue dividing the plant neurobiologists from their critics would appear to be this: Do capabilities such as intelligence, pain perception, learning, and memory require the existence of a brain, as the critics contend, or can they be detached from their neurobiological moorings? The question is as much philosophical as it is scientific, since the answer depends on how these terms get defined. The proponents of plant intelligence argue that the traditional definitions of these terms are anthropocentric—a clever reply to the charges of anthropomorphism frequently thrown at them. Their attempt to broaden these definitions is made easier by the fact that the meanings of so many of these terms are up for grabs. At the same time, since these words were originally created to describe animal attributes, we shouldn’t be surprised at the awkward fit with plants. It seems likely that, if the plant neurobiologists were willing to add the prefix “plant-specific” to intelligence and learning and memory and consciousness (as Mancuso and Baluška are prepared to do in the case of pain), then at least some of this “scientific controversy” might evaporate.
Indeed, I found more consensus on the underlying science than I expected. Even Clifford Slayman, the Yale biologist who signed the 2007 letter dismissing plant neurobiology, is willing to acknowledge that, although he doesn’t think plants possess intelligence, he does believe they are capable of “intelligent behavior,” in the same way that bees and ants are. In an e-mail exchange, Slayman made a point of underlining this distinction: “We do not know what constitutes intelligence, only what we can observe and judge as intelligent behavior.” He defined “intelligent behavior” as “the ability to adapt to changing circumstances” and noted that it “must always be measured relative to a particular environment.” Humans may or may not be intrinsically more intelligent than cats, he wrote, but when a cat is confronted with a mouse its behavior is likely to be demonstrably more intelligent.
Slayman went on to acknowledge that “intelligent behavior could perfectly well develop without such a nerve center or headquarters or director or brain—whatever you want to call it. Instead of ‘brain,’ think ‘network.’ It seems to be that many higher organisms are internally networked in such a way that local changes,” such as the way that roots respond to a water gradient, “cause very local responses which benefit the entire organism.” Seen that way, he added, the outlook of Mancuso and Trewavas is “pretty much in line with my understanding of biochemical/biological networks.” He pointed out that while it is an understandable human prejudice to favor the “nerve center” model, we also have a second, autonomic nervous system governing our digestive processes, which “operates most of the time without instructions from higher up.” Brains are just one of nature’s ways of getting complex jobs done, for dealing intelligently with the challenges presented by the environment. But they are not the only way: “Yes, I would argue that intelligent behavior is a property of life.”
To define certain words in such a way as to bring plants and animals beneath the same semantic umbrella—whether of intelligence or intention or learning—is a philosophical choice with important consequences for how we see ourselves in nature. Since “The Origin of Species,” we have understood, at least intellectually, the continuities among life’s kingdoms—that we are all cut from the same fabric of nature. Yet our big brains, and perhaps our experience of inwardness, allow us to feel that we must be fundamentally different—suspended above nature and other species as if by some metaphysical “skyhook,” to borrow a phrase from the philosopher Daniel Dennett. Plant neurobiologists are intent on taking away our skyhook, completing the revolution that Darwin started but which remains—psychologically, at least—incomplete.
“What we learned from Darwin is that competence precedes comprehension,” Dennett said when I called to talk to him about plant neurobiology. Upon a foundation of the simplest competences—such as the on-off switch in a computer, or the electrical and chemical signalling of a cell—can be built higher and higher competences until you wind up with something that looks very much like intelligence. “The idea that there is a bright line, with real comprehension and real minds on the far side of the chasm, and animals or plants on the other—that’s an archaic myth.” To say that higher competences such as intelligence, learning, and memory “mean nothing in the absence of brains” is, in Dennett’s view, “cerebrocentric.”
All species face the same existential challenges—obtaining food, defending themselves, reproducing—but under wildly varying circumstances, and so they have evolved wildly different tools in order to survive. Brains come in handy for creatures that move around a lot; but they’re a disadvantage for ones that are rooted in place. Impressive as it is to us, self-consciousness is just another tool for living, good for some jobs, unhelpful for others. That humans would rate this particular adaptation so highly is not surprising, since it has been the shining destination of our long evolutionary journey, along with the epiphenomenon of self-consciousness that we call “free will.”
In addition to being a plant physiologist, Lincoln Taiz writes about the history of science. “Starting with Darwin’s grandfather, Erasmus,” he told me, “there has been a strain of teleology in the study of plant biology”—a habit of ascribing purpose or intention to the behavior of plants. I asked Taiz about the question of “choice,” or decision-making, in plants, as when they must decide between two conflicting environmental signals—water and gravity, for example.
“Does the plant decide in the same way that we choose at a deli between a Reuben sandwich or lox and bagel?” Taiz asked. “No, the plant response is based entirely on the net flow of auxin and other chemical signals. The verb ‘decide’ is inappropriate in a plant context. It implies free will. Of course, one could argue that humans lack free will too, but that is a separate issue.”
I asked Mancuso if he thought that a plant decides in the same way we might choose at a deli between a Reuben or lox and bagels.
“Yes, in the same way,” Mancuso wrote back, though he indicated that he had no idea what a Reuben was. “Just put ammonium nitrate in the place of Reuben sandwich (whatever it is) and phosphate instead of salmon, and the roots will make a decision.” But isn’t the root responding simply to the net flow of certain chemicals? “I’m afraid our brain makes decisions in the same exact way.”
“Why would a plant care about Mozart?” the late ethnobotanist Tim Plowman would reply when asked about the wonders catalogued in “The Secret Life of Plants.” “And even if it did, why should that impress us? They can eat light, isn’t that enough?”
One way to exalt plants is by demonstrating their animal-like capabilities. But another way is to focus on all the things plants can do that we cannot. Some scientists working on plant intelligence have questioned whether the “animal-centric” emphasis, along with the obsession with the term “neurobiology,” has been a mistake and possibly an insult to the plants. “I have no interest in making plants into little animals,” one scientist wrote during the dustup over what to call the society. “Plants are unique,” another wrote. “There is no reason to . . . call them demi-animals.”
When I met Mancuso for dinner during the conference in Vancouver, he sounded very much like a plant scientist getting over a case of “brain envy”—what Taiz had suggested was motivating the plant neurologists. If we could begin to understand plants on their own terms, he said, “it would be like being in contact with an alien culture. But we could have all the advantages of that contact without any of the problems—because it doesn’t want to destroy us!” How do plants do all the amazing things they do without brains? Without locomotion? By focussing on the otherness of plants rather than on their likeness, Mancuso suggested, we stand to learn valuable things and develop important new technologies. This was to be the theme of his presentation to the conference, the following morning, on what he called “bioinspiration.” How might the example of plant intelligence help us design better computers, or robots, or networks?
Mancuso was about to begin a collaboration with a prominent computer scientist to design a plant-based computer, modelled on the distributed computing performed by thousands of roots processing a vast number of environmental variables. His collaborator, Andrew Adamatzky, the director of the International Center of Unconventional Computing, at the University of the West of England, has worked extensively with slime molds, harnessing their maze-navigating and computational abilities. (Adamatzky’s slime molds, which are a kind of amoeba, grow in the direction of multiple food sources simultaneously, usually oat flakes, in the process computing and remembering the shortest distance between any two of them; he has used these organisms to model transportation networks.) In an e-mail, Adamatzky said that, as a substrate for biological computing, plants offered both advantages and disadvantages over slime molds. “Plants are more robust,” he wrote, and “can keep their shape for a very long time,” although they are slower-growing and lack the flexibility of slime molds. But because plants are already “analog electrical computers,” trafficking in electrical inputs and outputs, he is hopeful that he and Mancuso will be able to harness them for computational tasks.
Mancuso was also working with Barbara Mazzolai, a biologist-turned-engineer at the Italian Institute of Technology, in Genoa, to design what he called a “plantoid”: a robot designed on plant principles. “If you look at the history of robots, they are always based on animals—they are humanoids or insectoids. If you want something swimming, you look at a fish. But what about imitating plants instead? What would that allow you to do? Explore the soil!” With a grant from the European Union’s Future and Emerging Technologies program, their team is developing a “robotic root” that, using plastics that can elongate and then harden, will be able to slowly penetrate the soil, sense conditions, and alter its trajectory accordingly. “If you want to explore other planets, the best thing is to send plantoids.”
The most bracing part of Mancuso’s talk on bioinspiration came when he discussed underground plant networks. Citing the research of Suzanne Simard, a forest ecologist at the University of British Columbia, and her colleagues, Mancuso showed a slide depicting how trees in a forest organize themselves into far-flung networks, using the underground web of mycorrhizal fungi which connects their roots to exchange information and even goods. This “wood-wide web,” as the title of one paper put it, allows scores of trees in a forest to convey warnings of insect attacks, and also to deliver carbon, nitrogen, and water to trees in need.
When I reached Simard by phone, she described how she and her colleagues track the flow of nutrients and chemical signals through this invisible underground network. They injected fir trees with radioactive carbon isotopes, then followed the spread of the isotopes through the forest community using a variety of sensing methods, including a Geiger counter. Within a few days, stores of radioactive carbon had been routed from tree to tree. Every tree in a plot thirty metres square was connected to the network; the oldest trees functioned as hubs, some with as many as forty-seven connections. The diagram of the forest network resembled an airline route map.
The pattern of nutrient traffic showed how “mother trees” were using the network to nourish shaded seedlings, including their offspring—which the trees can apparently recognize as kin—until they’re tall enough to reach the light. And, in a striking example of interspecies coöperation, Simard found that fir trees were using the fungal web to trade nutrients with paper-bark birch trees over the course of the season. The evergreen species will tide over the deciduous one when it has sugars to spare, and then call in the debt later in the season. For the forest community, the value of this coöperative underground economy appears to be better over-all health, more total photosynthesis, and greater resilience in the face of disturbance.
In his talk, Mancuso juxtaposed a slide of the nodes and links in one of these subterranean forest networks with a diagram of the Internet, and suggested that in some respects the former was superior. “Plants are able to create scalable networks of self-maintaining, self-operating, and self-repairing units,” he said. “Plants.”
As I listened to Mancuso limn the marvels unfolding beneath our feet, it occurred to me that plants do have a secret life, and it is even stranger and more wonderful than the one described by Tompkins and Bird. When most of us think of plants, to the extent that we think about plants at all, we think of them as old—holdovers from a simpler, prehuman evolutionary past. But for Mancuso plants hold the key to a future that will be organized around systems and technologies that are networked, decentralized, modular, reiterated, redundant—and green, able to nourish themselves on light. “Plants are the great symbol of modernity.” Or should be: their brainlessness turns out to be their strength, and perhaps the most valuable inspiration we can take from them.
At dinner in Vancouver, Mancuso said, “Since you visited me in Florence, I came across this sentence of Karl Marx, and I became obsessed with it: ‘Everything that is solid melts into air.’ Whenever we build anything, it is inspired by the architecture of our bodies. So it will have a solid structure and a center, but that is inherently fragile. This is the meaning of that sentence—‘Everything solid melts into air.’ So that’s the question: Can we now imagine something completely different, something inspired instead by plants?”
Source : The New Yorker
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The Claim: Exposure to Plants and Parks Can Boost Immunity
This time of year, allergies and the promise of air-conditioning tend to drive people indoors.
But for those who can take the heat and cope with the pollen, spending more time in nature might have some surprising health benefits. In a series of studies, scientists found that when people swap their concrete confines for a few hours in more natural surroundings — forests, parks and other places with plenty of trees — they experience increased immune function.
Stress reduction is one factor. But scientists also chalk it up to phytoncides, the airborne chemicals that plants emit to protect them from rotting and insects and which also seem to benefit humans.
One study published in January included data on 280 healthy people in Japan, where visiting nature parks for therapeutic effect has become a popular practice called “Shinrin-yoku,” or “forest bathing.” On one day, some people were instructed to walk through a forest or wooded area for a few hours, while others walked through a city area. On the second day, they traded places. The scientists found that being among plants produced “lower concentrations of cortisol, lower pulse rate, and lower blood pressure,” among other things.
A number of other studies have shown that visiting parks and forests seems to raise levels of white blood cells, including one in 2007 in which men who took two-hour walks in a forest over two days had a 50-percent spike in levels of natural killer cells. And another found an increase in white blood cells that lasted a week in women exposed to phytoncides in forest air.
THE BOTTOM LINE
According to studies, exposure to plants and trees seems to benefit health.
Source : The Times
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Plants that See, Feel, Smell and Remember
Scientist Daniel Chamovitz unveils the surprising world of plants that see, feel, smell—and remember
How aware are plants? This is the central question behind a fascinating new book, “What a Plant Knows,” by Daniel Chamovitz, director of the Manna Center for Plant Biosciences at Tel Aviv University. A plant, he argues, can see, smell and feel. It can mount a defense when under siege, and warn its neighbors of trouble on the way. A plant can even be said to have a memory. But does this mean that plants think — or that one can speak of a “neuroscience” of the flower? Chamovitz answered questions from Mind Matters editor Gareth Cook.
1. How did you first get interested in this topic?
My interest in the parallels between plant and human senses got their start when I was a young postdoctoral fellow in the laboratory of Xing-Wang Deng at Yale University in the mid 1990s. I was interested in studying a biological process that would be specific to plants, and would not be connected to human biology (probably as a response to the six other “doctors” in my family, all of whom are physicians). So I was drawn to the question of how plants sense light to regulate their development.
It had been known for decades that plants use light not only for photosynthesis, but also as a signal that changes the way plants grow. In my research I discovered a unique group of genes necessary for a plant to determine if it’s in the light or in the dark. When we reported our findings, it appeared these genes were unique to the plant kingdom, which fit well with my desire to avoid any thing touching on human biology. But much to my surprise and against all of my plans, I later discovered that this same group of genes is also part of the human DNA.
This led to the obvious question as to what these seemingly “plant-specific” genes do in people. Many years later, we now know that these same genes are important in animals for the timing of cell division, the axonal growth of neurons, and the proper functioning of the immune system.
But most amazingly, these genes also regulate responses to light in animals! While we don’t change our form in response to light as plants do, we are affected by lab at the level of our internal clock. Our internal circadian clocks keep us on a 24 hour rhythm, which is why when we travel half way around the world we experience jet lag. But this clock can be reset by light. A few years ago I showed, in collaboration with Justin Blau at NYU, that mutant fruit flies that were missing some of these genes lost the ability to respond to light. In other words, if we changed their clocks, they remained in jetlag.
This led me to realize that the genetic difference between plants and animals is not as significant as I had once naively believed. So while not actively researching this field, I began to question the parallels between plant and human biology even as my own research evolved from studying plant responses to light to leukemia in fruit flies.
2. How do think people should change how they think about plants?
People have to realize that plants are complex organisms that live rich, sensual lives. You know many of us relate to plants as inanimate objects, not much different from stones. Even the fact that many people substitute silk flowers for real ones, or artificial Christmas trees for a live one, is exemplary at some level of how we relate to plants. You know, I don’t know anyone who keeps a stuffed dog in place of a real one!
But if we realize that all of plant biology arises from the evolutionary constriction of the “rootedness” that keep plants immobile, then we can start to appreciate the very sophisticated biology going on in leaves and flowers. If you think about it, rootedness is a huge evolutionary constraint. It means that plants can’t escape a bad environment, can’t migrate in the search of food or a mate. So plants had to develop incredibly sensitive and complex sensory mechanisms that would let them survive in ever changing environments. I mean if you’re hungry or thirsty, you can walk to the nearest watering hole (or bar). If you’re hot, you can move north, if you’re looking for a mate, you can go out to a party. But plants are immobile. They need to see where their food is. They need to feel the weather, and they need to smell danger. And then they need to be able to integrate all of this very dynamic and changing information. Just because we don’t see plants moving doesn’t mean that there’s not a very rich and dynamic world going on inside the plant.
3. You say that plants have a sense of smell?
Sure. But to answer this we have to define for ourselves what “smell” is. When we smell something, we sense a volatile chemical that’s dissolved in the air, and then react in someway to this smell. The clearest example in plants is what happens during fruit ripening. You may have heard that if you put a ripe and an unripe fruit together in the same bag, the unripe one will ripen faster. This happens because the ripe one releases a ripening pheromone into the air, and the green fruit smells it and then starts ripening itself. This happens not only in our kitchens, but also, or even primarily, in nature. When one fruit starts to ripen, it releases this hormone which is called ethylene, which is sensed by neighboring fruits, until entire trees and groves ripen more or less in synchrony.
Another example of a plant using smell is how a parasitic plant called dodder finds its food. Dodder can’t do photosynthesis, and so has to live off of other plants. The way it finds its host plant is by smelling. A dodder can detect minute amounts of chemicals released in the air by neighboring plants, and will actually pick the one that it finds tastiest! In one classic experiment scientists showed that dodder prefers tomato to wheat because it prefers the smell.
3B. How about hearing?
This is a bit trickier because while loads of research support the idea that plants see, smell, taste and feel, support for plant auditory prowess is indirectly proportional to the amount of anecdotal information we have about the ways in which music may influence how a plant grows. Many of us have heard stories about plants flourishing in rooms with classical music. Typically, though, much of the research on music and plants was, to put it mildly, not carried out by investigators grounded in the scientific method. Not surprisingly, in most of these studies, the plants thrived in music that the experimenter also preferred.
From an evolutionary perspective, it also could be that plants haven’t really needed to hear. The evolutionary advantage created from hearing in humans and other animals serves as one way our bodies warn us of potentially dangerous situations. Our early human ancestors could hear a dangerous predator stalking them through the forest, while today we hear the motor of an approaching car. Hearing also enables rapid communication between individuals and between animals. Elephants can find each other across vast distances by vocalizing subsonic waves that rumble around objects and travel for miles. A dolphin pod can find a dolphin pup lost in the ocean through its distress chirps. What’s common in all of these situations is that sound enables a rapid communication of information and a response, which is often movement—fleeing from a fire, escaping from attack, finding family.
But plants are rooted, sessile organisms. While they can grow toward the sun, and bend with gravity, they can’t flee. They can’t escape. They don’t migrate with the seasons. As such, perhaps the audible signals we’re used to in our world are irrelevant for a plant.
All that being said, I have to cover myself hear by pointing out that some very recent research hints that plants may respond to sounds. Not to music mind you, which is irrelevant for a plant, but to certain vibrations. It will be very interesting to see how this pans out.
4. Do plants communicate with each other?
At a basic level, yes. But I guess it centers around how you define communication. There is no doubt that plants respond to cues from other plants. For example, if a maple tree is attacked by bugs, it releases a pheromone into the air that is picked up by the neighboring trees. This induces the receiving trees to start making chemicals that will help it fight off the impending bug attack. So on the face of it, this is definitely communication.
But I think we also have to ask the question of intent (if we can even use that word when describing plants, but humor me while I anthropomorphize). Are the trees communicating, meaning is that attacked tree warning its surrounding ones? Or could it be more subtle? Maybe it makes more sense that the attacked branch is communicating to the other branches of the same tree in an effort for self survival, while the neighboring trees, well they’re just eavesdropping and benefiting from the signal.
There are also other examples of this type of communication. For example a very recent study showed that plants also communicate through signals passed from root to root. In this case the “talking” plant had been stressed by drought, and it “told” its neighboring plants to prepare for a lack of water. We know the signal went through the roots because this never happened if the two plants were simply in neighboring pots. They had to have neighboring roots.
5. Do plants have a memory?
Plants definitely have several different forms of memory, just like people do. They have short term memory, immune memory and even transgenerational memory! I know this is a hard concept to grasp for some people, but if memory entails forming the memory (encoding information), retaining the memory (storing information), and recalling the memory (retrieving information), then plants definitely remember. For example a Venus Fly Trap needs to have two of the hairs on its leaves touched by a bug in order to shut, so it remembers that the first one has been touched. But this only lasts about 20 seconds, and then it forgets. Wheat seedlings remember that they’ve gone through winter before they start to flower and make seeds. And some stressed plants give rise to progeny that are more resistant to the same stress, a type of transgenerational memory that’s also been recently shown also in animals. While the short term memory in the venus fly trap is electricity-based, much like neural activity, the longer term memories are based in epigenetics — changes in gene activity that don’t require alterations in the DNA code, as mutations do, which are still passed down from parent to offspring.
6. Would you say, then, that plants “think”?
No I wouldn’t, but maybe that’s where I’m still limited in my own thinking! To me thinking and information processing are two different constructs. I have to be careful here since this is really bordering on the philosophical, but I think purposeful thinking necessitates a highly developed brain and autonoetic, or at least noetic, consciousness. Plants exhibit elements of anoetic consciousness which doesn’t include, in my understanding, the ability to think. Just as a plant can’t suffer subjective pain in the absence of a brain, I also don’t think that it thinks.
7. Do you see any analogy between what plants do and what the human brain does? Can there be a neuroscience of plants, minus the neurons?
First off, and at the risk of offending some of my closest friends, I think the term plant neurobiology is as ridiculous as say, human floral biology. Plants do not have neuron just as humans don’t have flowers!
But you don’t need neurons in order to have cell to cell communication and information storage and processing. Even in animals, not all information is processed or stored only in the brain. The brain is dominant in higher-order processing in more complex animals, but not in simple ones. Different parts of the plant communicate with each other, exchanging information on cellular, physiological and environmental states. For example root growth is dependent on a hormonal signal that’s generated in the tips of shoots and transported to the growing roots, while shoot development is partially dependent on a signal that’s generated in the roots. Leaves send signals to the tip of the shoot telling them to start making flowers. In this way, if you really want to do some major hand waving, the entire plant is analogous to the brain.
But while plants don’t have neurons, plants both produce and are affected by neuroactive chemicals! For example, the glutamate receptor is a neuroreceptor in the human brain necessary for memory formation and learning. While plants don’t have neurons, they do have glutamate receptors and what’s fascinating is that the same drugs that inhibit the human glutamate receptor also affect plants. From studying these proteins in plants, scientists have learned how glutamate receptors mediate communication from cell to cell. So maybe the question should be posed to a neurobiologist if there could be a botany of humans, minus the flowers!
Darwin, one of the great plant researchers, proposed what has become known as the “root-brain” hypothesis. Darwin proposed that the tip of the root, the part that we call the meristem, acts like the brain does in lower animals, receiving sensory input and directing movement. Several modern-day research groups are following up on this line of research.
Source : Scientific American
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