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.