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There is a very profound question

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that you see on the screen.

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If a tree falls in a forest -- and no one is around to hear it,

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does it make a sound?

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You all know this question and this question is attracting

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the attention of philosophers for over a 300 years.

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But this question, very question, would seem

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totally ridiculous to the plants neighboring this tree,

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which for many decades listened to messages

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and signals coming from this fallen tree.

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So today I'm going to tell you something

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about plant communication

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and something about the ways

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plants learn from each other about their environment.

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We all know something about that communication.

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Plants communicate with animals all the time.

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Not necessarily with fancy mammals like us

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but more with little creatures like the insects

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and the birds you see on the screen.

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They attract them by putting out very flashy flowers

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to make sure that they are pollinated.

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This is part of their sex life.

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This is one way they communicate.

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Another way is to --

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They need some transition services for their seeds.

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Therefore they make flashy fruits

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and put some little sweet candies inside

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so mammals and other creatures will carry them away

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to new places, to new environments.

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This is communication - look at the colors.

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This is not only communicating with us.

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This is communicating with very many other creatures.

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But these are very simple ways

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that the plants are taking

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relying on the services made by animals.

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This is all relying on the fact

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that those animals have some brains.

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They can decide whether to choose fruits,

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whether to visit a flower.

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This is using the brain of the animal.

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There is some decision, motor, engine behind it.

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Not of the plant - the animal.

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But in our research, we are trying to do something else.

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We try to find out whether plants can communicate

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between themselves, with other plants.

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And one nice example is by the phenomenon

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we call talking trees.

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This is not from our own studies but from other studies --

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other studies from the other laboratories around the world.

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Trees are stuck in the same place - most of them.

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Once they're germinated they are bound to stay there

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for the rest of their lives.

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Sometimes for hundreds of years.

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They cannot run away

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and this is making their lives very difficult because

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there are very many creatures [who] are out to get them.

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Many insects, mammals and other creatures

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can simply come and bite their head off.

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If they won't do anything good about it.

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And one way - there are many ways the plants

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defend themselves against this munching -

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but one way is to put out

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or to accumulate all kinds of nasty chemicals.

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Once they have the chemicals,

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they deter some of those grazers, herbivores -

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all kinds of animals that want to munch on them.

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And, in fact, they do something else too.

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Once there is some munching on the plant,

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some plants are capable of putting out

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all kinds of odors - volatile materials,

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which become airborne and picked up by other parts

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of the same plant and other nearby neighbors.

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Which, only when they get this message,

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this communication from another plant,

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start to produce toxins,

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which deter any attack - by insects in this case.

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This is pretty sophisticated behavior

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for brainless creatures, I would say.

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What else can they chat about? (Laughter)

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And this is something that we are dealing with in our group.

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We are asking specifically in one of our projects:

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Can plants eavesdrop - listen to the hardships,

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the stresses their neighbors undergo.

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And use this information

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to resist and survive better in the future.

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Imagine the following situation.

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There is a plant. Something bad happens to it -

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stress like drought or high levels of salt -

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we all know very well from this country, and it is stressed.

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It is doing miserably. But now I am asking

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whether a neighbor plant, which is totally

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or seemingly oblivious to the stress of the other plant,

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would sense the information,

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get the communication and do something about it.

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I am asking about the red arrow here.

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So how do we do this?

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All you need is a bunch of seed[ling]s

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and a knife or a pair of scissors.

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You cut off the root of a plant -

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it would regenerate immediately many other roots.

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And you can choose, carefully choose, which is very easy

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to do for a five-year old, plants with only two roots.

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And if they put out six, you take away four,

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you leave them with two - more or less identical -

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and you put them together like this:

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sharing one pot in the middle.

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Sharing a pot in the middle allows them

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to communicate if they choose to do so.

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This is allowing a route of communication between the roots.

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Obviously, there is another channel for communication.

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Among the leaves using the same mechanism

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we were discussing before,

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through [volatile chemicals] in the air.

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So what can we do?

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We just stress one root of one of the plants

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and we ask - obviously we know that this guy

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is going to be miserable about it - and we ask

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whether the other guy will do something about it too.

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OK? What do we measure?

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We want something, which is simple to study,

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simple to measure, and we want a rapid response -

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something physiological, which is easy to pick up.

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And one of those things is the way

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plants keep their leaves open or close

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when they are facing a problem.

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What you see here,

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thousands of times enlarged on the screen,

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is little pores every plant has in its leaves

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through which it is exchanging gas

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with its environment.

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These pores are openable, they are very flexible.

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It's like little shutters -

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they can close and open very-very swiftly -

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through which they absorb CO2 and emit O2, oxygen.

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By the way, which allows us

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to resist and survive and to live on this planet.

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So when the plant is happy, it is opening the stomata,

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there is no outlook for any stress,

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and this is how they look - open stomata.

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Stomata are the little wholes. And when the plant

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is unhappy, or expecting some problem,

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for instance drought, it is closing those little pores.

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And this is measurable, we can take a photograph

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and measure it very easily.

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So happy plants. We take a set of plants like this:

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the one we are going to induce a stress to and a neighbor

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and when there is no stress they are happy.

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Nice and happy - look at the stomata -

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they are smiling at you.

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They are so happy about it.

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But what if I stress - by draught -

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one root of one of the plants?

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It is miserable, closing its stomata,

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the little holes, the little pores,

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but also the neighbor - which was never harmed,

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never stressed before - feels something.

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There is communication. Why to eavesdrop?

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Why should an unstressed neighbor

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use such an information? It was not stressed!

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Well, in many cases, if my neighbor is stressed now,

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there is a very high chance that I am going to be stressed

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in a few minutes, a few hours or a few days.

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So better prepare for this.

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Preparation for future is something

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extremely important in the evolution

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and in the ecology of any creature.

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The more interesting and more difficult question is

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why the stressed neighbor would allow

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or give such information to its neighbors.

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After all they can be its enemies, its competitors.

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Well, in many cases plants are tremendously large.

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They can be as large as a few football fields.

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They can weigh hundreds of tons in biomass.

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They can be tremendously large.

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When attack is happening in one corner or one bunch,

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there is a very good rationale

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to disperse the information to the rest of the plant.

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Some of them can be large by cloning.

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They have many twin parts which spread over

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like in the lawn grasses in your back yard.

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Or the strawberries you eat. Or the birch trees.

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They are all clonal. They have very many members

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which are connected together.

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Some of which are severed from each other, disconnected.

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So it's a good idea to disperse the news, the warning.

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Stress is happening. So if this logic is correct,

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I would expect something even more elaborate.

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That a non-stressed plant would share the information with its neighbors.

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Not only the stressed plant would share, but also

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the unstressed neighbor would share the information

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with further, with more neighbors. OK?

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Testing it is simple. Now you know the method,

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you can be a scientist as me.

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You take this system, which we already know

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what happens in - the first neighbor is responding,

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there is communication,

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and we simply add more neighbors.

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And we ask the same question.

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Would this information be relayed to them?

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Would this unstressed neighbor share the information

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with additional neighbors?

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And this is after fifteen minutes. Fifteen short minutes!

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Three plants were closing their stomata.

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So there was relay,

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there was sharing by unstressed plants.

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And in on hour only, all five plants in a row,

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and if I would work hard enough,

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and my people would work hard enough,

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I bet you it would reach the tenth plant too.

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So there is both communication and sharing

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of the information by unstressed individuals here.

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This is all by plants having no brains - remember that!

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So far so good, but we've been showing

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the communication and the sharing of the information

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but we haven't proven yet that this was happening

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through the root communication.

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This was all done by a system sharing roots, right?

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In order to prove or to test whether it was through the root

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or through the shoots, the leaves above ground,

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through volatile chemicals, we have to add another set

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of plants which were not sharing the roots.

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And, indeed, when plants are not sharing the roots,

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there is no communication in this case.

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Which is a direct proof that communication

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of such stress signals is going between the roots.

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But there is a more profound question here. After all,

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stomata, as I already declared, work extremely rapidly.

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They can open and close in a few seconds,

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in a few minutes, they can reopen

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after a few seconds, a few moments.

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And indeed this is what they are doing

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after getting the "cry wolf" warning signals.

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So this is a little fishy or might be fishy,

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maybe it's not so essential,

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maybe it's not significant for the real life.

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And the profound question here is to ask

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whether plants would learn from their past experiences

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and counter with a stressed plant and get better

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in facing and surviving hardships in the future -

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in this case a drought.

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And the way to test this is very simple.

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You take the very same system you already know.

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A row of plants sharing the root systems in the dirt pots:

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in one case you don't stress them,

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and in another case you do stress.

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What do we stress and not stress?

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One root of one plant in the row. That's it!

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And then we expose the entire system to real drought.

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And here is the real test!

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In real life, not just blinking your pores, right?

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In real life.

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So this is the happy plant,

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which never got any exposure to stressed neighbor,

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and after one month it's bone dry!

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As would be expected in Israeli green-house

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40 °C degrees in summer.

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OK, this is not surprising anyone here.

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But this guy, this set, got one of the roots

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of one of the plants exposed to drought

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before the experiment started,

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before the exposure to drought started.

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And one month later, this is how it looks!

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This is not by giving it more water!

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This is by the plants getting an experience,

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the communicative experience, of facing a neighbor

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that once in the past was exposed to drought,

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using the information, storing it somehow

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and using it later in life

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and better survive and resist drought in the future.

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This is both learning and memory

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of brainless creatures.

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And this is a big lesson!

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The lesson is from the humble creatures

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which have no brain but can learn, memorize

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and use the environmental information later on

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for better survivorship.

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I want to thank the members of my lab:

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Dr. Omer Falik, who over-viewed the process

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and most of the experiments, Ishay Hoffman,

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Yonat Mordoch, Daniel Ben-Natan Sion,

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Miri Vanunu and Oron Goldstein;

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and the generous financial support

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of the Israel Science Foundation.

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Thank you very much!

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(Applause)