Why do plants need nerve impulses

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

Centuries-old oaks, lush grass, fresh vegetables - somehow we are not accustomed to considering plants as living creatures, and in vain. Experiments show that plants have a kind of complex analogue of the nervous system and, just like animals, are able to make decisions, store memories, communicate, and even give each other gifts.

Professor of Oakwood University Alexander Volkov helped to understand in more detail the electrophysiology of plants.

Journalist: I never would have thought that someone was doing plant electrophysiology until I came across your articles

Alexander Volkov:You are not alone. The general public is used to seeing plants as food or landscape elements without even realizing that they are alive. Once I was doing a report on the electrophysiology of plants in Helsinki, and then my colleagues were very surprised: “I used to deal with a serious topic - immiscible liquids, but now I was dealing with some kind of fruits and vegetables”. But this was not always the case: the first books on the electrophysiology of plants were published in the 18th century, and then the study of animals and plants proceeded in almost parallel ways. For example, Darwin was convinced that the root is a kind of brain, a chemical computer that processes signals from the entire plant (see, for example, "Movement in Plants"). And then the First World War came and all the resources were thrown into the study of the electrophysiology of animals, because people needed new drugs.

W: It seems logical: laboratory mice are still much closer to humans than violets

A. V:In reality, the differences between plants and animals are not at all so huge, and in electrophysiology they are generally minimal. Plants have an almost complete analogue of a neuron - phloem conductive tissue. It has the same composition, size and function as neurons. The only difference is that in animals, sodium and potassium ion channels are used in neurons to transmit action potentials, while in plant phloem, chloride and potassium ion channels are used. That's the whole difference in neurophysiology. The Germans have recently found chemical synapses in plants, we are electrical, and in general, plants have the same neurotransmitters as animals. It seems to me that this is even logical: if I were creating the world, and I am a lazy person, I would make everything the same so that everything is compatible.

Why do plants need nerve impulses?

We don't think about it, but plants in their life process even more types of signals from the external environment than humans or any other animals. They react to light, heat, gravity, salt composition of the soil, magnetic field, various pathogens and flexibly change their behavior under the influence of the information received. For example, in the laboratory of Stefano Mancuso of the University of Florence, experiments were carried out with two climbing bean shoots. Scientists established a common support between the plants, and the shoots began to race to it. But as soon as the first plant climbed onto the support, the second immediately seemed to recognize itself as defeated and stopped growing in this direction. It understood that the struggle for resources is meaningless and it is better to look for happiness somewhere else.

W: Plants do not move, grow slowly and generally live unhurriedly. It seems that their nerve impulses should also propagate much more slowly

Alexander Volkov: This is a delusion that has long existed in science. In the 70s of the XIX century, the British measured that the action potential of the Venus flytrap spreads at a speed of 20 centimeters per second, but this was a mistake. They were biologists and did not know the technique of electrical measurements at all: in their experiments, the British used slow voltmeters, which recorded nerve impulses even slower than they propagated, which is completely unacceptable. Now we know that nerve impulses can run through plants at very different speeds, depending on the place of signal excitation and on its nature. The maximum speed of propagation of action potentials in plants is comparable to the same indicators in animals, and the relaxation time after the passage of the action potential can vary from milliseconds to several seconds.

W: What do plants use these nerve impulses for?

A. V: A textbook example is the Venus flytrap, which I have already mentioned. These plants live in areas with very moist soil, which is difficult for air to penetrate, and, accordingly, there is little nitrogen in this soil. Flycatchers get the lack of this essential substance by eating insects and small frogs, which they catch with an electric trap - two petals, each of which has three piezomechanical sensors built into it. When an insect sits on any of the petals and touches these receptors with its paw, an action potential is generated in them. If an insect touches the mechanosensor twice within 30 seconds, then the trap is slammed shut in a split second. We checked the operation of this system - we applied an artificial electrical signal to the trap of the Venus flytrap, and everything worked in the same way - the trap was closed. Then we repeated these experiments with mimosa and other plants and so we showed that it is possible to force plants to open, close, move, bend down - in general, do whatever you want, using electrical signals. In this case, external excitations of a different nature generate action potentials in plants, which can differ in amplitude, speed and duration.

W: What else can plants react to?

A. V: If you cut the grass in your country house, then action potentials will immediately go to the roots of the plants. The expression of some genes will start on them, and the synthesis of hydrogen peroxide is activated on the cuts, which protects plants from infection. In the same way, if you change the direction of the light, then for the first 100 seconds the plant will not react to it in any way, in order to cut off the option of a shadow from a bird or an animal, and then electrical signals will again go, according to which the plant will turn in seconds in such a way as to maximize capture the luminous flux. All the same will happen, and when you start dripping boiling water, and when you bring up a burning lighter, and when you put the plant in ice - plants react to any stimuli with the help of electrical signals that control their responses to changed environmental conditions.

Plant memory

Plants not only know how to react to the external environment and, apparently, calculate their actions, but also tie up some social relations among themselves. For example, the observations of the German forester Peter Volleben show that trees have a kind of friendship: partner trees are intertwined with roots and carefully monitor that their crowns do not interfere with each other's growth, while random trees do not have any special feelings for to their neighbors, they always try to grab for themselves more living space. At the same time, friendship can also arise between trees of different types. So, in the experiments of the same Mancuso, scientists observed how, shortly before the death of Douglas, it seems that it leaves a legacy: a yellow pine tree not far from it sent a large amount of organic matter through the root system.

W: Do plants have memory?

Alexander Volkov: Plants have all the same types of memory as animals. For example, we showed that the Venus flytrap has memory: for the trap to work, you need to send 10 microcoulombes of electricity to it, but it turns out that this does not have to be done in one session. You can first serve two microcoulomb, then another five, and so on. When the total is 10, it will seem to the plant that an insect has got into it, and it will slam shut. The only thing is that you cannot take breaks of more than 40 seconds between sessions, otherwise the counter will reset to zero - you get such a short-term memory. And the long-term memory of plants is even easier to see: for example, one spring frost hit us on April 30, and literally overnight all the flowers froze on the fig tree, and the next year it did not bloom until May 1, because it remembered what it was. ended. A lot of similar observations have been made by plant physiologists over the past 50 years.

W: Where is plant memory stored?

A. V: Once I met at a conference in the Canary Islands Leon Chua, who at one time predicted the existence of memristors - resistances with the memory of the passed current. We got into a conversation: Chua knew almost nothing about ion channels and electrophysiology of plants, I - about memristors. As a result, he asked me to try to search for memristors in vivo, because according to his calculations, they should be associated with memory, but so far no one has found them in living beings. We did it all: we showed that the voltage-dependent potassium channels of aloe vera, mimosa, and the same Venus flytrap are memristors by nature, and in the following works, memristive properties were found in apples, potatoes, pumpkin seeds, and different flowers. It is quite possible that the memory of plants is tied precisely to these memristors, but it is not yet known for sure.

W: Plants know how to make decisions, have a memory. The next step is social interactions. Can plants communicate with each other?

A. V: You know, in Avatar there is an episode where trees communicate with each other underground. This is not a fantasy, as one might think, but an established fact. When I lived in the USSR, we often went to pick mushrooms and everyone knew that the mushroom must be carefully cut with a knife so as not to damage the mycelium. Now it turns out that the mycelium is an electrical cable through which trees can communicate both with each other and with mushrooms. Moreover, there is plenty of evidence that trees exchange not only electrical signals along the mycelium, but also chemical compounds or even dangerous viruses and bacteria.

W: What can you say about the myth that plants understand human speech, and therefore you need to talk to them kindly and calmly so that they grow better?

A. V: This is just a myth, nothing else.

W: Can we apply the terms "pain", "thoughts", "consciousness" to plants?

A. V: I don't know anything about this. These are already questions of philosophy. Last summer in St. Petersburg there was a symposium on signals in plants, and several philosophers from different countries came there at once, so this topic is now starting to be dealt with. But I am used to talking about what I can experimentally test or calculate.

Plants as sensors

Plants are able to coordinate their actions using branched networks. Thus, the acacia growing in the African savanna not only releases a toxic substance into its leaves when giraffes begin to eat it, but also emits a volatile "alarm gas" that sends a distress signal to surrounding plants. As a result, in search of food, giraffes have to move not to the nearest trees, but to move away from them on average 350 meters. Today scientists dream of using such networks of living sensors, debugged by nature, for environmental monitoring and other tasks.

W: Have you tried to put your plant electrophysiology research into practice?

Alexander Volkov: I have patents for predicting and registering earthquakes using plants. On the eve of earthquakes (in different parts of the world, the time interval varies from two to seven days), the movement of the earth's crust causes characteristic electromagnetic fields. At one time, the Japanese proposed to fix them with the help of giant antennas - pieces of iron two kilometers high, but no one could build such antennas, and this is not necessary. Plants are so sensitive to electromagnetic fields that they can predict earthquakes better than any antenna. For example, we used aloe vera for these purposes - we connected silver chloride electrodes to its leaves, recorded electrical activity, and processed the data.

W: Sounds absolutely fantastic. Why hasn't this system been put into practice yet?

A. V: There was an unexpected problem here. Look: let's say you are the mayor of San Francisco and find out that there will be an earthquake in two days. What are you going to do? If you tell people about this, then as a result of panic and crush, even more people may die or be injured than in an earthquake. Because of such restrictions, I cannot even publicly discuss the results of our work in the open press. In any case, I think sooner or later we will have a variety of monitoring systems operating on sensor plants. For example, in one of our work, we have shown that using the analysis of electrophysiological signals, it is possible to create a system for the instant diagnosis of various diseases of agricultural plants.

More on the topic:

Plant mind

Language of plants