The Secret Language of Plants | SLICE SCIENCE | FULL DOC

Plants have sensory capacities that are far more sophisticated than we once imagined. Plants move, smell, taste, listen, memorize. Deprived of a nervous system, they are somehow capable of recognizing their family, sending out an alarm signal, and even communicating. Plants are everything but silent. In the 1960s, Cleve Baxter, a trained member of the CIA interrogation team, made a revelation that marked its era. Plants, he affirmed, are capable of communicating between each other. Using a lie detector, he claimed to have succeeded in capturing their thoughts, emotions, and even their telepathic powers. Attached to delicate electronic instruments, a cabbage plant registers annoyance to the exhaling of tobacco smoke on its leaf surfaces. A scene familiar in any kitchen takes on special importance in this experiment. In some mysterious way, the plant which is attached to the instrument is able to feel the mutilation of its comrade. Baxter was not a scientist, and he did a lot of experiments, but claiming that he was able to detect telepathy and a big amount of strange phenomena in plants. But in the last 40 years, many, many scientists tried to repeat the experiment without success. So essentially, in science, if you cannot repeat an experiment, this means that this experiment is wrong. The authors rarely did experiments in the way a scientist would do them, so most scientists dismissed it as not very scientific. The secret life of plants was looking at plant social life in a very New Age-y kind of way. Stefano Mancuso is not a survivor from the New Age. A pioneer in neurobiological research on plants, he is convinced that plants are great communicators. At the University of Florence in Italy, he is trying to reveal what plants are hiding from us. Stefano Mancuso's first trial is with a bean plant. He has grown them under various conditions. In the dark, at different lighting or humidity levels, at varied temperatures, even by modifying the magnetic field that surrounds it. He wants to find out how the bean plants always find the support stick. We did some 100 different experiments, and all the times, the plants were able to find the supports. Now the idea is that there is some kind of unknown way that the plants use to sense the environment. Skeptical scientists have objected, declaring that the plant is performing a simple mechanical movement, and that the plant haphazardly found the nearby support stick. In reply to the critics, Stefano Mancuso placed two plants, one on each side of the stick. As he expected, both plants grew towards the support stick. Our science is a science made by animals, for animals. Because we are animals, we are unable normally to feel that plants are intelligent and sensitive organisms. Dare we evoke a form of plant brain? Intelligence and sensitivity is not something that is linked to a brain. The brain, in itself, is a stupid organ. It's just an amount of cells that we have here, and every animal has. But if you look at the single cells, they are cells. There is nothing mysterious or supernatural about the cells of our brains. They are just a kind, a specific kind of cells called neurons. But you don't need neurons to make this stuff. You can have all other kinds of cells having the same function. So it means transmitting signals from one cell to the other. The tremendous root network that plants possess makes a striking parallel with our highly complex brain circuits. Charles Darwin was one of the first to probe the underground life of plants. He was convinced that plants have command centers at the tip of their roots, known as the apex. Researcher at the University of Bonn in Germany, Dr. Frantisek Belusco works on apex neurobiology. All the root epices, they are coordinated in their activities and growth and they resemble some swarms, for example, insect swarms or birds, as somehow there is some communication. We still don't understand how it is going on, but they are coordinating and behave as one swarm. Frantisek Belusco's research has revealed that within the apex, plants have cells that are very similar to those found in animal muscle cells. The roots are capable of exploring the soil with extraordinary precision and plants seem to know when to form their flowers or drop their leaves. Could there really be, as Charles Darwin once thought, a single and unique command post? There is no central organizer and that's why these networks are not vulnerable to some stress situations. These networks can self-organize very effectively and they can survive any bad stress situation. The network resembles very closely the internet network, so one could call it a root wide web. A root wide web. Root cells that function independently, but in coordination with others. This is the same kind of signal we can record in the animal brain. Really, these networks are also used to exchange information, not just to provide water or nutrition. We have still no idea how complex the communication there is. Today, we are aware that plants have much to talk about, but we know little or nothing of it. The secret life of plants is slowly unveiled through the research of a few tenacious scientists. Canadian biologist Susan Dudley and her team have found that when the root of the impatiens pallida touches the root of a plant from another family, the impatiens increases its water and light consumption and creates larger leaves. Okay, 20.1 square centimeters. It's a good-sized leaf. These plants are big. These plants actively know that they have neighbors and actively respond to the presence of neighbors, and each and every leaf, in fact, positions itself to avoid getting shaded by neighboring leaves, even within the same plant. But the impatiens' reaction is totally different when its roots come across a family member. We can say that plants know who members of the same family are, and that's important information for them to know because members of the same family share genes, and so if you're nice to a member of the same family, if you compete less with it or even actively share with it, then your genes are being passed on through that family member. Using such tactile root recognition, the plant can advantage its family members. This reveals that plants, in their own way, are capable of altruism. Just as amazing, plants are able to communicate between themselves other than by touch, as Dr. Stefano Mancuso demonstrates. Our Italian scientist has isolated three groups of corn plants. There is no root contact between them. He will then deprive oxygen to one of the groups. After five minutes from the start of the lack of oxygen, we had this group of plants emitting an SOS signal to warn the surrounding plant that there is something that is going wrong with oxygen. In this case, we have a group of plants that are emitting a message that is, in a few words, pay attention, there is no more oxygen around. And the other group of plants are receiving this message and according, they are able to prepare themselves to a future lack of oxygen. Here we have the plants that are without any change in the oxygen and that are not receiving any message. Here we have the plants in red that are producing a gene because they are stressed by the lack of oxygen and they are producing also a message and the message is taken by the blue plants. They have no problem with oxygen but they are all the same producing the gene because they are receiving the message. So definitely there is a communication between these two groups of plants. Plants can send and receive messages but how do they do it? They are really speaking to each other. It's not a kind of language like our language. It's not based on words but it's based on chemical molecules. Plants are able to produce many thousands of chemical molecules. Each single molecule means something. So when this group of plants are producing specific molecules and this other group of plants are detecting this molecule this means that there is something wrong. Plants have invented alarm signals to warn their neighbors of an imminent danger. They also practice the art of chemical self-defense. This strange landscape is that of the stinging nettle where a cocktail of molecules, fungicides and insecticides contain a well-known irritating resin. Hidden beneath their skin are numerous molecules that scientists are only beginning to recognize. On the tomato leaf these mushroom-looking stems are topped by four cells that contain a repulsive resin that will be released when under attack by a pest. And that's not all. Plants have the amazing ability to release chemical signals that will attract the enemies of their voracious predators. This is the case of corn when it is attacked by the Spidoptera a small caterpillar that has a strong appetite for its leaves. These herbivorous insects do enormous damage and they cost the American farmers but also European farmers millions of dollars or euros. To win any battle it's an advantage to have allies. The Campyletus sonorensis female is the natural enemy of the Spidoptera caterpillar. But just how does this parasite wasp detect such a tiny caterpillar in a giant cornfield? What we were initially thinking is that they would respond to the feces of these caterpillars or perhaps the body odors of the caterpillars themselves. Feces in our minds is something that is very smelly and that would be a very reliable source of signals that these wasps could use. But then we were studying this in more detail and we found that the plants that have been attacked by these caterpillars were much more attractive than feces or the caterpillars themselves. And that's when we started focusing on the signals that the plants produce. To his surprise, Ted Terlings found that the damaged corn leaf releases a particularly odorous molecule. A specific SOS signal that attracts the caterpillar's enemies. This indicator is like a GPS location signal for wasps who can then target the tiny invisible caterpillar in the heart of the immense cornfield. So that was of course a very exciting moment because we started realizing the plant is doing something to get the enemies of their enemies come and kill the caterpillars. Plants do not communicate like you and I do that but they transmit information to other organisms like these parasitic wasps through odors. One single caterpillar munching on a corn leaf releases the odors that attract the wasps. That's what this olfactometer reveals. But the alarm signal is not immediately released. Several hours will have passed between the first caterpillar bite and the liberation of volatile substances. The plant will then produce odors that will soon be emitted by all of its leaves. The feeding by the caterpillar is not really the same as if you would damage a leaf yourself. So you know if you damage a leaf you can smell that there is a volatile coming off so there's an odor coming off. But in the case of caterpillar feeding they actually have something in their spit that the plants recognize and the plants start then producing a different odor that they produce from all the leaves also the leaves that are not damaged and that results in a specific signal that alerts these parasitic wasps. These odors are produced to attract the enemies of their enemies. Corn calls upon an insect to do its dirty work. This is the secret route of evolution. Plants have no way to move, no way to physically directly defend themselves, start fighting with their enemies and eventually this results in some sort of communication between plant and insect. Even more astounding, the intensity of the signal varies with the age of the plant. One caterpillar can in fact kill a small plant. We find also indeed that the smaller plants send off much stronger signals, many more of these compounds from these odors than the older plants. But the caterpillar has adopted a new tactic. To trick the enemy, it has changed its feeding times. The odors are not produced at night or at least in much smaller quantities because photosynthesis is necessary and for photosynthesis you need light. The corn plant has forced the caterpillars to adopt a new strategy. To survive, they must devour the corn leaves at night. Another species has started an assault on the corn's roots. Diabrodica, the corn worm, is in full-fledged destruction mode. They work their way inside the root where they are well protected and then they work their way up all the way to the top of the roots, causing the root to completely be destroyed. Also making sure that the plant cannot take up water anymore. The stability of the plant is lost and in many cases the plant will fall over and there's no corn produced. The team of scientists want to find out if the corn roots can also send underground warning signals to attract other natural enemies of the Diabrodica worm. Nematodes barely visible to the naked eye. Will the nematodes be guided by the plant in order to localize the Diabrodica worm and eliminate it? We have released nematodes at about half a meter away from the roots and they are later, within a day, found near those roots and killing these insects. And for a nematode, which is less than a millimeter long, that's an enormous distance. So that would be 500 times their body length. Most likely all plants can communicate and the more and more we study this, the more and more we realize that there are plenty of other things to be discovered that we cannot see what their plants are doing to defend themselves. If plants have to watch their backs, they must also think ahead about their reproduction. And again, chemical signals play a key role. This orchid has adopted qualities from the animal kingdom to resemble and smell just like an insect. The flower is so similar to a female wasp that males are instantly attracted and appear to prefer the plant. Over evolutionary time, any mutation that arose in the plant that caused the flower to resemble an insect a little more was retained and flowers that didn't look so much like an insect didn't make a living, didn't reproduce and we wind up with a flower that looks ever more like an insect. As surprising as it may seem, the orchid releases chemical signals very similar to the female wasp's sexual pheromones. The male is fooled by both the plant's odor and visual strategies. For the flower, the chances of insemination increase. In reward, the wasp will leave with more pollen. The same signals that insects use to communicate with each other for sex are biochemically very similar to some of the signals plants are using to talk to each other and biochemically very similar to hormones that we have in our body for signaling as well. Life has evolved using a common set of signals and communication between different organisms often involves signal stealing. The ability to take your signals and use them in my life in a way that benefits me. Plants are not only capable of releasing pleasant or unpleasant odors. They can smell them too. How can plants perceive the chemical molecules that are sent to them? This is the key question entomologist Consuela de Moraes has been asking. Her speciality, Cuscuta, a vampire plant that particularly parasites tomato plants. They have a very small seed and they only have the resources that are on those seeds to grow and find a host plant. So once they emerge from the ground, if they don't find a host, they will die. What we found is that plants perceive the odors of other plants and what we believe it's happening is that they have receptors. I think for the tomato plant, it's just a byproduct of their physiology and attracting the Cuscuta is just happening. Like we are producing a smell that attract mosquitoes that we're not intended to do it, but we're doing it. Every human being has a specific odor. Plants do too. The electron microscope unveils the odorous glands of the tomato plant leaf. Numerous on the leaves of tomato or cannabis plants, they liberate intense odors. Each plant has a specific olfactory signature expressed by the morphology of its odorous glands and the powerful perfume of lavender is explained by its large olfactory pockets. The electron microscope reveals countless release glands, but plants also have many invisible receptors. They have, I mean, in my view, an incredible sense. They really can sniff. One thing that we were amazed to see is that the Cuscuta have this ability also to perceive, you know, a healthy plant versus a sick plant. I think it's possible that it is some of the receptors that we see in animal system, insect systems, could be some similarities. I mean, not the same, but I think it's possible that there are some similarities. Unfortunately, our sense of smell is of no use to decrypt the chemical messages sent by plants. We are unable to crack their code, but scientists are never defeated. Everything we know about this has been studied in the laboratory. It's extremely difficult to get a picture of that rainbow of chemical words in the field because we really don't have the instruments necessary to collect and analyze them. If we are to master the invisible conversations of plant life, we will have to learn to translate their chemical vocabulary into words. The device we're devising is rather like a translator. It takes the language of the plant, which is all odors, and turns it into something we can see, hear or feel so the plant can tell us or report to us what's happening to it. A key word that often appears in the plant language is methyl jasminate, a molecule that harbors the smell of the jasmine flower. Highly appreciated by humans, it is frequently used in the perfume industry. Almost all plants emit some methyl jasminate when they're attacked by insects. So that appears to be a word that occurs in all languages. But the devil is in the details. All the other molecules mixed in with it can differ from plant to plant and that's where the language gets complicated. Plants have a slower life rhythm than humans. Some are capable of living several thousand years, but they cannot run away from danger. In response, they have developed remarkable ways to detect problems or swiftly react to the aggression of an insect. It's a question of survival. If we count the number of protein receptors plants have for smelling and tasting their environment, they have many, many, many more than a human does. Even a simple plant has at least 600 different kinds of receptors for detecting odors and tastes in the environment. In contrast, humans have fewer than 20. Plants are furnished with a multitude of strange stalks and hairs that serve as receptors and protection against insects. Their vast diversity is the secret to evolutionary adaptation against the many threats. In order to compensate our lack of sensory receptors, Jack Schultz is working on a prototype of an artificial nose, a highly sensitive plaque that he hopes will enable us to improve our comprehension of the chemical conversations of plants. Well, we created this chip or this sensing device to be able to ask plants what they're saying outdoors in open air for the first time. Everything we know about how plants communicate is based on work done in laboratories under glassware. No one has yet isolated and measured and mapped those signals and those conversations outdoors. And we plan to be the first people to do that with this device. The interaction between insects and plants we describe as a war all the time, and that war is chemical. And those chemicals are invisible. So it's very true to say that there is chemical warfare and invisible communication going on all around us all the time. If plants have so many receptors, are they conscious that the person taking care of them is their best friend? Can the plants in the home recognize you? I suppose they might. But certainly, plants in your home are capable of identifying your odor. Plants are capable of smelling our odors. But can they hear us? Plants are, it seems, receptive to music. The first experiments held 40 years ago said that plants were sensitive to classical music, but did not like artificial or electronic music like rock or blues. In the heart of Tuscany in Italy, a rather surprising scientific experiment has been undertaken by Dr. Stefano Mancuso over the past seven years. 24 hours a day, seven days a week, the music of Mozart is played to the vines. What we saw immediately after a few weeks of times was that the plants with the music were much bigger and much productive. But at that time, we didn't know if it was just the effect of music or the effect of soils or the climate or whatever. And so we decided to move on a larger scale experiment, moving from just one loudspeaker to 80 speakers in a single vineyard. Dr. Mancuso has revealed some rather surprising results. The number of insect attacks was really dramatically decreasing until almost nothing, almost zero. The sounds were able to make a kind of confusion in the insects during the mating process. So they were unable to find the mate and so they were unable to reproduce. After several years spent playing Mozart to the vineyard, Stefano Mancuso is formal. The grapes on those land areas ripen 10 to 15 days before normal harvest dates. Plants are highly sensitive to sound. But just how do they hear them? Plants have no ears, but the plants are completely covered by mechanosensitive channels. I would say small sensors that are activated by vibrations. Plants are probably much more sensitive than us in detecting sounds. An in-depth examination by electron microscope reveals that the leaves and the tendrils of the vines are covered by sensors that could well be their ears. Stefano Mancuso has discovered which frequencies the vines appreciate the most and subtly inserted them in Mozart's orchestrations. We found that there are a range of frequencies in the low part of the spectrum, around 100, between 100 and 1000 hertz. There are many frequencies that we could say plants like. But just what good does it do to the plant to detect such sound vibrations? We are not sure about what actually the plants do with this information. But we are quite sure that plants are able to use the information coming from the sounds in the soil, for example, to detect the quality of the soils, the amount of water in the soils, the presence of obstacles in the soil. So they are in some way using information coming from sounds to have an idea of the space around them. Our image of the plant, stupid and inert, is to be reconsidered. And plants certainly haven't finished surprising us. For the first time ever, Stefano Mancuso has discovered that plants also emit sounds. Yes, they talk. Of weak intensity, these little clicking sounds are possibly the first to be recorded of corn roots detected by a laser. If they can talk, do they have a language? Can they memorize a vocabulary? Are they equipped with a memory? Memory is something that has been heavily underestimated in plants. These plants are separated into two groups. During two weeks, Stefano Mancuso injected small quantities of zinc into one of the two groups. Zinc is a heavy metal dangerous to the plant. On the 15th day, he injected high doses of zinc to both groups. The plants that had previously received the weak doses of zinc better survived under this shock treatment. This means that plants are able to solve a problem, to learn how to solve a problem, and the next time that they are presented with the same problem, they are able to solve it better. It's a form of memory. Interpreting visual signals released by plants that could be beneficial to humankind is the work of botanist Ida Godel. She has developed the art of predicting the weather forecast by closely observing the behavior of plants in the Swiss Alps, which anticipate from several hours to several days. What can Alcamilla tell us about tomorrow's weather? This droplet of water is always found inside the plant. And it's not a dewdrop. It's something that the plant produces. It does this all the time, non-stop. The only time it doesn't make droplets is when it's going to rain. Forecasting the weather by observing plants requires patience and immense observation. Ida Godel's father was a horticulturist, and she spent her childhood carefully observing plant life with him. Each time I had a question concerning a plant, to know where it came from, what it was doing here, father nearly always had the right answer. The oxeye daisy is the big sister of the common daisy. It's a great deal heavier, so it needs a lot more time to open and close. It's far slower in its forecasts. With its lunar structure on the tip of its stem, the flower is composed of white petals that will slowly close upon nightfall, but also to protect itself in case of bad weather. You have to watch them every day and have a different approach. All plants react. Be they outside in the garden or inside your house, they react in exactly the same way. A cactus in your apartment can tell you the weather forecast. Weather-sensitive plants are numerous. Daisies, dandelions, tulips, roses, thistles, geraniums, but also pines, beech, oaks or even grasses, clovers, lily pads, lettuces, even onion skins. It's by observing these plants that Ida Godel predicted the heat wave that hit Europe in the summer of 2003. I would say it's a very precise science. The plant is never wrong. It's a question of survival. The only person that could make a mistake is me, in its interpretation. If our ancestors were able to read the weather forecast through plant behavior, perhaps tomorrow plants could become excellent sentinels in detecting dangerous substances. Dr. Jack Schultz is trying to create plants that will become our allies. He hopes they will react in a specific way under certain situations. Creating plants that report danger is something we call sentinel plants. We would create a sentinel plant that changes color in response to something it detects, sits on your desk or in the corner of the room, and acts as a canary in the mine. Changes color, speaks up, if you will, when it detects whatever you would like it to tell you about. We can use genetic engineering to create plants now that respond very quickly by changing color, losing their greenness, producing more volatiles. And if we were able to do that, we could place plants in locations where they could very quickly report the presence of something we wanted to know about, for example, chemical weapons. Placed in strategic locations such as airports, plants could become very useful in detecting drugs, chemical products and explosives. Highly toxic to humankind, the chemical composition of TNT is actually very good for plants. TNT is an excellent fertilizer due to its high levels of nitrogen. Plants grow really, really well on TNT-contaminated soils. In a minefield, each mine has explosives in it, and those explosives slowly leak out of the mine, creating a circle of fertilized soil where plants grow really well. If we were to sow a field, imagine a desert in Iraq or something, with a plant that grows quickly, you would expect to see nice green patches grow over each of the landmines. Rather than seeking to enslave plants, to make the most of them, perhaps we could also attempt to communicate with them in a more poetic manner. And through a specific kind of artistic technology, we manage to perceive what the plant is feeling. This interactive garden is composed of genuine musical plants that react to our contact, a vegetal language generated by touch. When visitors caress them or brush up against them, the plants will sing. It is not the voice of the plant, but a sound chosen by the artists, set off by the visitor. We wanted to give plants a voice. When you look at a plant, it doesn't give us the impression that they can speak, they seem so inert and silent. We gave them a whole new universe of sound from nature, forests, animals or insects. In our exhibition, they're heard in an abstract dimension. When we work with the invisible, we're interested in finding new boundaries to sketch the imperceptible, suggest it and make it sensitive. It's not oral communication, it's not a dialogue but an exchange of sensations. If the plant dies, it ceases to sing. We are unable to comprehend the complex language of plants, but our scientists are well aware that plants do communicate, be it through the ground or thin air, using hundreds of chemical signals. They can talk to each other and even to other animals. Perhaps they are even trying to communicate with us. It's impossible for us to imagine how a plant could sense. If we can crack the code of plant language, then plants will be speaking to us all the time. Should we manage to pierce their secret language, we may be surprised at what they have to say. Could it be that they are manipulating our very brains to reach their goals? Perhaps they influence us in the same way they influence insects. Corn may well be manipulating our taste buds, similar to the way it guides the parasitic wasp towards the Spidoptera caterpillar. And who knows if the world of green will not one day turn against humans, considered in turn as ravagers.