Feel mushrooms and plants pain
The senses of the plants
Summary: No way "stupid greenery" - plants produce amazing sensory performances. Trees and plants do not have nerve cells. But they produce hormones with which they transmit sensory stimuli through a fine network of veins to their own organs - this is how they feel, see, hear and communicate.
Look out the window. Do you see a tree there? How it rises into the sky, steady and still, at most moving the leaves by the wind? Perhaps you are a little touched by so much age, stability and immobility. You may be a little worried that your tree will fall victim to the next urban pruning. Or the neighbour's obsession with order, at whose garden edge he stands. Like many other people, you feel a certain sympathy for the large wooden monument there in your field of vision where possible. For the cool canopy in hot summer. For the empty filigree of the branches in the winter sky. He is beautiful as he stands there, motionless and stoic. But he probably doesn't notice what is going on around him, and feels neither fear nor pain. Or does it?
Look again. And then follow František Baluška's words. The tall Slovak with the spherical, bald skull is doing research at the Botanical Institute of the University of Bonn. Together with a few hundred other biologists around the world, Baluška explores how plants perceive their environment, how they communicate with each other and with other living beings. In the past few years, a few things have emerged here that are changing our ideas about plants, but also about living things as a whole. Look at the tree, fixed and immobile. Follow the trunk into the earth, into a compact and humid world that tastes of nutrient salts, a world of tiny corridors between grains of sand, filled with the bodies of fungi, root hairs, unicellular organisms, bacteria and small vertebrates. The tree lives in this crowded cosmos, the surface of which represents an impenetrable border for us. Without us knowing much about it.
“Imagine that a plant is as big under the ground as it is above,” recommends Baluška. An old beech tree as high as a six-story house extends its roots in the ground as far as its crown. Not in depth alone, but rather in breadth. The roots branch out, split up, branch out into billions of hair-thin tips. And these tips are in motion. They wander through the earth without ceasing. At one millimeter per hour, each end of the root pushes through the soil, driven by the cells that grow back. Incessantly. Miles. “Think of each root tip like an astronaut being carried through the dark universe by his spaceship,” says Baluška.
And like an astronaut, each tip can determine its own path. The roots touch grains of sand, they smell salts, they accompany microscopic water veins on their way. And they identify the roots of young saplings that have sprouted from the seeds of their own tree body, wrap them protectively, and nourish them with sugar solution. On the surface, in our sphere, the tree stands still. Beneath it his fingers wander through the depths, even in winter he is in motion. “The real life of the plant takes place underground,” says Baluška. “In truth, what we call the ground is a web of moving plant bodies.” The leaves above only soak up the energy in the sky. Would you have imagined a plant like this? Just. Neither do most botanists.
The science of plants is in an exciting mood of change. While large genetic engineering companies try to program maize and soy like robots for higher yields, less water consumption and resistance to pesticides, botanists are finding more and more indications that plants are not motionless lumps of matter, no bio-automats, no, as Baluška likes to say, “zombies”. Currently, one crack after the other pervades our long dominant image of the passive plant, which is basically nothing more than a self-growing raw material for the construction and furniture industry as well as stupid green fodder. The gap we postulated between animals - agile, sensitive, endowed with a brain - and the unconscious "vegetating" plants is increasingly closing.
A number of researchers today believe that plants are not only intelligent, like animals too. Like them, they have an interest in their own existence, which they want to preserve by all means. They have a point of view, a perspective and react immediately to what happens to them. What biologists learn about the abilities of plants also helps us to revise our conception of life. And that does not remain without effects on our image of ourselves.
TED-Talk: The botanist Stefano Mancuso explains why plants have their own intelligence
“Biology is facing a Copernican turn”, predicts the Italian botanist Stefano Mancuso, who runs the “Plant Neurobiology Laboratory” at the University of Florence. At the end of the Middle Ages, the astronomer Nicolaus Copernicus discovered that the earth revolved around the sun, replacing the idea of the Greek scholar Ptolemy that the earth was at the center of the universe. In a similar way, the long-standing assumption of many biologists that plants are basically unconscious machines is being revised by new discoveries of their ability to experience and feel. Mancuso is convinced: plants are not only in full possession of all five senses that we humans have, they also have a lot more that we previously did not even dare to dream of. For magnetic fields, for example, or for chemicals.
"Today we know: plants talk to each other, recognize their relatives and show very different, individual characters," says Mancuso. The man in his mid-fifties is sitting in his laboratory in front of a pin board that is hung with printouts of beauties from the botanical kingdom: orchid blossoms, old trees, landscapes. A map of the world spreads out next to it: the researcher - thin gray beard, nimble eyes behind stylish glasses - could be a humanities scientist instead of a laboratory practitioner. And Mancuso is actually not just about routine research, but about the big unsolved questions: “I deal with plants because I want to know what life is. Because that's not clear at all. Most researchers just don't admit it. ”For Mancuso, especially in science, an overly human-fixated point of view prevents us from perceiving other beings as they are. We cannot recognize their abilities - and certainly not recognize them.
Seeing, hearing, touching, smelling, tasting - is it really possible that the rigid growths are not only as flexible in some parts of the body as small animals, but that they have an equally differentiated perception of the world? To give his listener a helping hand, Mancuso reminds them that it is of little use if we compare our own abilities one-to-one with those of the plants. Rather, we have to take the point of view of the plants - look at the world through the eyes of sedentary beings that eat light, so to speak.
It starts with the eyes. Plants are blind, right? Because, unlike almost all animals, they have no visual cells. Mancuso gently helps: If we describe seeing as the ability to react sensibly to differences in light, then plants can not only see, but are downright masters at it. Because light is their real food. In order to thrive, plants have to capture the light and grow towards it optimally. "We can imagine that basically the whole body of the plant is covered with eyes," says Mancuso. Or rather: the plant is a single eye. Not only the leaves, all surfaces of the plant body contain receptors for brightness - so that green can quickly grow there in an emergency.
Plants have eleven different light sensors, seven more in their eyes than humans. The US botanist David Chamovitz discovered in recent years that the same genes in plants, animals and humans are responsible for light regulation. Chamovitz is certain: "You see plants when you approach them and when you bend over them."
That might sound like an adventure. The houseplant does not recognize its caretaker, who water it with loving care, as a silhouette against the background of the surroundings. “Plants translate light signals into a growth impulse,” says Chamovitz. The plant friend appears to the object of her concern as threatening shade, from which the sprouts are better able to strive away. The basil at the window, the sprouting potato locked in a box, do not photograph the surroundings, but transform themselves into the image of the light by stretching towards it and absorbing its energy.
And this stretching takes a while. During this time, we fast-moving animals have long since turned to other objects. Without taking into account the factor of the much slower proper time, it is difficult to imagine how active plants are. The duration of perception is too different from the vegetable and animal perspective. But when we translate the slowness of the plants into our own hectic pace, a lot becomes clearer. We basically have to learn to think in fast motion.
Mancuso did that. The Italian patiently filmed how bean tendrils fish for a pole that they can wind up on. Up until now it was believed that the encounter with a plant tendril was pure coincidence, that the plant grasped what it found. But the videos show: Apparently the bean knows what it is doing - and where it has to go and whom. In the time-lapse view of the camera, it grows towards the pole as if it were a hand that is purposefully reaching for a hold.
In addition to the sense of touch, which enables the tips of the shoots to wrap around the support - according to plant standards - at lightning speed, the bean must also have other sensory abilities. Does it work with an echo sounder? Does she smell the metal of the staff? Mancuso is not sure. But he is convinced that the offspring does not act randomly, but with a fixed goal. Those who watch the films find it difficult to escape this feeling.
Manusco's colleague Chamovitz confirms the obstinacy with which tendrils look for their favorite place. He looked at how a parasitic American grapevine targeted other plants in order to sink their suckers into their tissues. Grapevines are happy to take tomatoes as a source of nutrients - but, if possible, disdain wheat stalks.
TED-Talk: The botanist Stefano Mancuso explains why plants have their own intelligence
It has now been established that the parasitic climbing plant smells the differences between individual species. She reacts intensively to “Eau de Tomato”, says Chamovitz, but less to “Eau de Wheat”. But can one really speak of “smell” here? Isn't that what you need a nose for? "When a plant converts a chemical signal in the air into a certain behavior, then something is called a sense of smell," explains Chamovitz briefly. While animals are primarily oriented towards waves - some energy oscillations are perceived by them as light, others as heat, air vibrations as sound - reality is conveyed to plants as a scent in the form of gas particles that the plants send and receive. “Researchers know around 2,000 fragrance words from 900 plant families,” estimates the Swiss geneticist and plant researcher Florianne Koechlin. This "cell whisper", as Koechlin calls it, is picked up by other plants, but also by insects and vertebrates.
Plant gases often serve to protect themselves from attack by voracious insects; conspecifics are prepared at the same time. The Lima bean produces a fragrance when attacked by mites. In addition, the plant secretes sweet nectar at the base of its leaves. This attracts ants that attack the mites. The scent of gas causes other plants nearby to do the same and open their nectar glands to ward off the threat.
But that's not all: A subsequent wave of scent causes the bean plant to attract predatory mites, which also eat the parasitic mites. What kind of tormentors are who suck on it, the plant can taste from the saliva of the parasites that penetrate its tissue, says Koechlin. Because if a caterpillar rather than a mite gnaws at its green, the sapling emits a different gas that attracts parasitic wasps, which specialize in butterfly larvae. "How many animals can use such sophisticated defense strategies?" Asks Mancuso in view of this sophistication.
The fragrances of plants are therefore often signal carriers and active ingredients in one, the effects of which are not limited to the plant kingdom. Tobacco plants sound the alarm with nicotine and at the same time use the substance, which is poisonous for animals, to repel pests. When green growths are attacked by viruses or bacteria, they release the gas methyl salicylate, which is closely related to the main component of the anti-inflammatory and pain reliever aspirin. The substance kills the intruders in the leaf tissue - at the same time other herbs in the area are warned.
Another universal plant gas was previously used successfully as an anesthetic in humans, explains František Baluška, and it was considered a miracle drug with almost no side effects: ethylene. Ethylene only had one problem: it is highly explosive. After a few operating rooms that went up in flames, the anesthetists stopped his use. The plant world continues to use the active ingredient. Recently, researchers discovered that injured mimosas emit ethylene - and at the same time have an anesthetic effect on them.
“It almost seems as if a plant can put itself under anesthesia if it is injured,” says Baluška. Up until now, ethylene was primarily known as a fragrance that coordinates fruit ripening. Ripe fruits expel the chemical, thereby speeding up the ripening process of other nearby fruits. That is why a hard avocado will soften quickly if you put it in a paper bag with a ripe banana.
But can that also mean that the fruits, the flesh of which consists of living cells to the end, numb themselves before they are inevitably eaten? Is the scent of freshly mown hay, the aroma of ripe melons, for the affected plants really an anesthetic that makes it easier for them to die, as some researchers believe? Some botany professors shake their heads at such speculations. They complain about colleagues who deal with the perceptual abilities of plants. Too esoteric, too speculative. Too little scientific. Most of all, the botanists, who often think traditionally, resent their guild members when they recently called their field of research “plant neurobiology”.
Neurobiology - the word is simply wrong, they say. Because only animals have neurons, i.e. nerves. And, according to the prevailing dogma, without nerves there can be no intelligence, no experience, no learning, no individuality, no feeling of pain: "No brain, no pain", is how the US botanist Lincoln Taiz from the University of California sums it up in Santa Cruz together. David Robinson, who conducts research at the Heidelberg Institute for Plant Sciences, considers the hypothesis of his colleagues that plants are capable of experiences that animals need nerves for as “complete nonsense”. He is convinced: “This stupid idea will soon die out.” And Elmar Hartmann, botanist at the Free University of Berlin, believes that the questions posed by researchers in search of plant intelligence and the ability to experience will open the door wide to esotericism will.
“German professors in particular insist on the dogma that a plant is actually a machine,” says Mancuso. "They offer the greatest resistance to a new assessment of the plants." Plants do not have any synapses that would report an injury to a central authority such as the brain. But their communication works just as well, he says, when the signal substance envelops an entire tree and drifts through the forest. Only the principle of signal transmission is different from that of animals.The fauna often consists of colonies of the same plant, in which it is not at all clear which stem grows from which root shoot. The gas shower informs distant parts of the own body about a possible danger as well as offshoots that grow a little further away, as well as conspecifics in the vicinity.
Experiments show that plants can remember the past and even learn without neuronal pathways. If a laboratory researcher regularly flips his fingers over the sensitive tip of a young maize plant, for example, the plant remains smaller than usual, but becomes very stocky, reports Florianne Koechlin. And the botanist Monica Gagliano from the University of Western Australia has found that young mimosa plants quickly get used to jerky movements if the plants find that the shaking has no bad consequences.
Usually a mimosa, when given a push, closes its fine leaf panicles in a flash. But Gagliano's saplings quickly got used to repeated shaking movements - but immediately contracted as soon as their leaves were touched in any other way. “We normally only find this form of learning in animals,” says the botanist. At the congress in Vancouver, Canada, at which Gagliano presented her work last year, there was a riot of skepticism.
Charles Darwin and his son Francis had already experienced resistance in the 19th century. Already at that time they suggested that intelligent behavior should be ascribed to the root tips of the plant, but the advance ended in the barrage of the botanist Julius von Sachs, who was researching at the University of Würzburg at the time. Sachs called Darwin, who had just developed the epochal theory of evolution, a “country scholar”, a dilettante who could not hold a candle to a trained plant researcher.
Today František Baluška complains that a climate prevails again in botany that opposes new thinking. “Today, many scientists no longer propose theories, but slavishly stick to dogmas from the past,” he says. But good science doesn't work according to this principle. New results should not be thrown out because they shake old beliefs. Progress in knowledge will only be possible at all if researchers get involved with what does not fit into the picture.
In concrete terms, this means that if plants show that learning is also conceivable without nerves, if memories can be stored not only in the brain but also in the body, then biologists may have to revise their understanding of what life means. Then ultimately every cell could be capable of experience - and in a certain way also "intelligent". Because what does that even mean, intelligence? Does intelligent action have to be defined in such a way that a brain plans all actions centrally? For Mancuso, intelligence simply means: being able to constructively solve the problems of one's own existence. The American philosopher Daniel Dennett gives Mancuso support on this point: Dennett says that mind and consciousness are in principle a consequence of evolution. But evolution never has just one solution. In this respect, a view that chains intelligence, learning and memory of the existence of neurons and brains is hopelessly “cerebrocentric”, an “outdated myth”.
Even the sophisticated human brain itself is not hierarchical. Researchers have known that for a long time. For centuries they had been looking for a center, for a control authority, a "homunculus" who is in command of the command center. Today it is clear that the thinking organ of animals - including that of humans - creates its cohesion from a chaotic network of nerve groups that are often connected to one another. These form centers and associations - and yet are criss-crossed with one another.
Ironically, there is hardly anything that resembles the web-like interweaving of our cranial nerves more than the network of roots and fungi in the forest floor. Here, too, there are extensive connections from certain centers - the plant's root zones. Not just between individuals of the same tree species, but between different plants, and above all between plants and the fine fungal threads. Baluška believes that without this close connection to mushrooms, which supply the plant roots with minerals and in return receive sugar juice, the green plants would never have been able to colonize the land.
Canadian forest ecologist Suzanne Simard studies the relationships within this network, which literally fills every cavity in the ground. She injected a weakly radioactive liquid into tree roots and measured how this marking substance was distributed. When she followed the path of the fabric, she found out that every tree in a 30 square meter forest area was connected to the "Wood Wide Web" of the roots and fungal threads. In this botanical internet, older specimens feed young saplings until they are big enough to gain enough energy from the sunlight. And not just within their own species: when winter began, even pines and birches exchanged nutrients with each other.
Simard believes that the benefits of this mutual donation give the forest ecosystem as a whole greater stability and individual individuals more resilience. Perhaps Charles Darwin, who is revered for clarifying the “origin of species” but is still laughed at by some for his work on botany, will be right here in the long run. For Darwin, every single root tip could be compared in its cognitive ability with the brain of a worm.
We are back in the ground below the tree. Everything is in motion. Each of the billions of rootworms dig their way through the grains of sand, connect with threads of fungus, weave around their own kind, share their food and perceive themselves and their surroundings. Everything is full of living experience.
Perhaps today we should even go a little further than Darwin and say with the Swiss geneticist Florianne Koechlin: The soil with its roots is a kind of brain. One that does not set itself apart, but one that “thinks” by constantly creating and strengthening new connections. We humans would probably still have a lot to learn from this brain.
(NG, issue 8/2015, page (s) 88 to 111)
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