In this talk, Professor Ariel Novoplansky discusses about the unique way in which plants communicate through their roots.
Ariel Novoplansky – TEDx Talk TRANSCRIPT
There is a very profound question that you see on the screen. If a tree falls in a forest — and no one is around to hear it, does it make a sound? You all know this question and this question is attracting the attention of philosophers for over 300 years.
But this question, very question, would seem totally ridiculous to the plants neighboring this tree, which for many decades listened to messages and signals coming from this fallen tree.
So today I’m going to tell you something about plant communication and something about the ways plants learn from each other about their environment.
We all know something about that communication. Plants communicate with animals all the time. Not necessarily with fancy mammals like us but more with little creatures like the insects and the birds you see on the screen.
They attract them by putting out very flashy flowers to make sure that they are pollinated. This is part of their sex life. This is one way they communicate Another way is to — They need some transition services for their seeds. Therefore they make flashy fruits and put some little sweet candies inside so mammals and other creatures will carry them away to new places, to new environments.
This is communication – look at the colors. This is not only communicating with us. This is communicating with very many other creatures. But these are very simple ways that the plants are taking relying on the services made by animals. This is all relying on the fact that those animals have some brains.
They can decide whether to choose fruits, whether to visit a flower. This is using the brain of the animal. There is some decision, motor, engine behind it. Not of the plant – the animal.
But in our research, we are trying to do something else. We try to find out whether plants can communicate between themselves, with other plants. And one nice example is by the phenomenon we call talking trees. This is not from our own studies but from other studies — other studies from the other laboratories around the world.
Trees are stuck in the same place – most of them. Once they’re germinated they are bound to stay there for the rest of their lives. Sometimes for hundreds of years. They cannot run away, and this is making their lives very difficult, because there are very many creatures that are out to get them.
Many insects, mammals and other creatures can simply come and bite their head off. If they won’t do anything good about it. And one way – there are many ways the plants defend themselves against this munching – but one way is to put out or to accumulate all kinds of nasty chemicals.
Once they have the chemicals, they deter some of those grazers, herbivores – all kinds of animals that want to munch on them. And, in fact, they do something else too. Once there is some munching on the plant, some plants are capable of putting out all kinds of odors – volatile materials, which become airborne and picked up by other parts of the same plant and other nearby neighbors.
Which, only when they get this message, this communication from another plant, start to produce toxins, which deter any attack – by insects in this case. This is pretty sophisticated behavior for brainless creatures, I would say.
What else can they chat about? And this is something that we are dealing with in our group. We are asking specifically in one of our projects: Can plants eavesdrop – listen to the hardships, the stresses their neighbors undergo and use this information to resist and survive better in the future?
Imagine the following situation. There is a plant. Something bad happens to it – stress like drought or high levels of salt – we all know very well from this country, and it is stressed. It is doing miserably.
But now I am asking whether a neighbor plant, which is totally or seemingly oblivious to the stress of the other plant, would sense the information, get the communication and do something about it. I am asking about the red arrow here.
So how do we do this? All you need is a bunch of seedlings and a knife or a pair of scissors. You cut off the root of a plant – it would regenerate immediately many other roots. And you can choose, carefully choose, which is very easy to do for a five-year old, plants with only two roots.
And if they put out six, you take away four, you leave them with two – more or less identical – and you put them together like this: sharing one pot in the middle. Sharing a pot in the middle allows them to communicate if they choose to do so. This is allowing a route of communication between the roots.
Obviously, there is another channel for communication. Among the leaves using the same mechanism we were discussing before, through volatile chemicals in the air. So what can we do?
We just stress one root of one of the plants and we ask – obviously we know that this guy is going to be miserable about it – and we ask whether the other guy will do something about it too. OK?
What do we measure? We want something, which is simple to study, simple to measure, and we want a rapid response – something physiological, which is easy to pick up. And one of those things is the way plants keep their leaves open or close when they are facing a problem.
What you see here, thousands of times enlarged on the screen, is little pores every plant has in its leaves through which it is exchanging gas with its environment. These pores are openable, they are very flexible. It’s like little shutters – they can close and open very-very swiftly – through which they absorb CO2 and emit O2, oxygen.
By the way, which allows us to resist and survive and to live on this planet. So when the plant is happy, it is opening the stomata, there is no outlook for any stress, and this is how they look – open stomata.
Stomata are the little wholes. And when the plant is unhappy, or expecting some problem, for instance drought, it is closing those little pores. And this is measurable, we can take a photograph and measure it very easily.
So happy plants. We take a set of plants like this: the one we are going to induce a stress to and a neighbor and when there is no stress they are happy.
Nice and happy – look at the stomata – they are smiling at you. They are so happy about it.
But what if I stress – by drought – one root of one of the plants? It is miserable, closing its stomata, the little holes, the little pores, but also the neighbor – which was never harmed, never stressed before – feels something. There is communication.
Why to eavesdrop? Why should an unstressed neighbor use such an information? It was not stressed! Well, in many cases, if my neighbor is stressed now, there is a very high chance that I am going to be stressed in a few minutes, a few hours or a few days.
So better prepare for this. Preparation for future is something extremely important in the evolution and in the ecology of any creature. The more interesting and more difficult question is why the stressed neighbor would allow or give such information to its neighbors. After all they can be its enemies, its competitors. Well, in many cases plants are tremendously large.
They can be as large as a few football fields. They can weigh hundreds of tons in biomass. They can be tremendously large. When attack is happening in one corner or one bunch, there is a very good rationale to disperse the information to the rest of the plant. Some of them can be large by cloning.
They have many twin parts which spread over like in the lawn grasses in your back yard. Or the strawberries you eat. Or the birch trees. They are all clonal. They have very many members which are connected together.
Some of which are severed from each other, disconnected. So it’s a good idea to disperse the news, the warning. Stress is happening. So if this logic is correct, I would expect something even more elaborate. That a non-stressed plant would share the information with its neighbors.
Not only the stressed plant would share, but also the unstressed neighbor would share the information with further, with more neighbors. OK? Testing it is simple.
Now you know the method, you can be a scientist as me. You take this system, which we already know what happens in – the first neighbor is responding, there is communication, and we simply add more neighbors. And we ask the same question.
Would this information be relayed to them? Would this unstressed neighbor share the information with additional neighbors? And this is after fifteen minutes. Fifteen short minutes! Three plants were closing their stomata.
So there was relay, there was sharing by unstressed plants. And in an hour only, all five plants in a row, and if I would work hard enough, and my people would work hard enough, I bet you it would reach the tenth plant too. So there is both communication and sharing of the information by unstressed individuals here.
This is all by plants having no brains – remember that! So far so good, but we’ve been showing the communication and the sharing of the information but we haven’t proven yet that this was happening through the root communication.
This was all done by a system sharing roots, right? In order to prove or to test whether it was through the root or through the shoots, the leaves above ground, through volatile chemicals, we have to add another set of plants which were not sharing the roots.
And, indeed, when plants are not sharing the roots, there is no communication in this case. Which is a direct proof that communication of such stress signals is going between the roots. But there is a more profound question here.
After all, stomata, as I already declared, work extremely rapidly. They can open and close in a few seconds, in a few minutes, they can reopen after a few seconds, a few moments. And indeed this is what they are doing after getting the “cry wolf” warning signals.
So this is a little fishy or might be fishy, maybe it’s not so essential, maybe it’s not significant for the real life. And the profound question here is to ask whether plants would learn from their past experiences and counter with a stressed plant and get better in facing and surviving hardships in the future – in this case a drought.
And the way to test this is very simple. You take the very same system you already know. A row of plants sharing the root systems in the dirt pots: in one case you don’t stress them, and in another case you do stress. What do we stress and not stress? One root of one plant in the row. That’s it! And then we expose the entire system to real drought.
And here is the real test. In real life, not just blinking your pores, right? In real life. So this is the happy plant, which never got any exposure to stressed neighbor, and after one month it’s bone dry. As would be expected in Israeli green-house 40 °C degrees in summer. OK, this is not surprising anyone here.
But this guy, this set, got one of the roots of one of the plants exposed to drought before the experiment started, before the exposure to drought started. And one month later, this is how it looks. This is not by giving it more water. This is by the plants getting an experience, the communicative experience, of facing a neighbor that once in the past was exposed to drought, using the information, storing it somehow and using it later in life and better survive and resist drought in the future.
This is both learning and memory of brainless creatures. And this is a big lesson.
The lesson is from the humble creatures which have no brain but can learn, memorize and use the environmental information later on for better survivorship.
I want to thank the members of my lab: Dr Omer Falik, who over-viewed the process and most of the experiments, Ishay Hoffman, Yonat Mordoch, Daniel Ben-Natan Sion, Miri Vanunu and Oron Goldstein; and the generous financial support of the Israel Science Foundation.
Thank you very much.