Learning Plant Learning: Prof. Ariel Novoplansky at TEDxJaffa

Summary

This script explores the fascinating world of plant communication, revealing that plants can 'talk' to each other through chemical signals, especially in response to stress. The speaker discusses 'talking trees' and how plants can prepare for stress by eavesdropping on their neighbors' experiences. Experiments show that plants can share stress signals through their roots, leading to a collective response that enhances survival. The script challenges the notion that learning and memory are exclusive to brain-equipped organisms, highlighting the complex adaptive behaviors of plants.

Takeaways

• 🌳 Plants communicate with each other using signals, like volatile chemicals released in response to stress.
• 🦋 Plants communicate with animals, such as insects and birds, by attracting them with colorful flowers and fruits for pollination and seed dispersal.
• 🌱 When a plant is attacked or stressed, it can send out airborne signals that alert nearby plants to prepare for potential threats.
• 🌿 Neighboring plants can detect these signals and adjust their physiological responses, such as closing their stomata to conserve water.
• 🧪 Researchers have shown that plants can 'eavesdrop' on their neighbors and prepare for stress even if they themselves haven't been affected yet.
• 👥 Plants sharing root systems can communicate stress signals more effectively, leading to shared defensive behavior among connected plants.
• 🧠 Even though plants lack brains, they can learn from past experiences and use this information to survive future challenges, such as drought.
• ⏳ The transmission of stress signals between plants can happen rapidly, within minutes, causing neighboring plants to react accordingly.
• 🔬 Experiments have demonstrated that plants can 'remember' past stressful events and perform better under similar conditions later, showing signs of learning and memory.
• 👨‍🔬 The research highlights the sophisticated and intelligent behavior of plants, despite their lack of a central nervous system, pointing to the complexity of plant survival strategies.

Q & A

What is the philosophical question discussed in the beginning of the script?

The philosophical question discussed is, 'If a tree falls in a forest and no one is around to hear it, does it make a sound?' which has been a topic of interest for philosophers for over 300 years.

How do plants communicate with each other according to the script?

Plants communicate with each other through chemical signals, such as volatile organic compounds, and by sharing roots which allow direct communication between them.

What is the term used for plants that can send signals to other plants when they are under attack?

The term used for this phenomenon is 'talking trees'.

How do plants attract pollinators and ensure seed dispersal?

Plants attract pollinators by producing flashy flowers and attract seed dispersers by creating flashy fruits with sweet rewards inside.

What is the role of stomata in a plant's response to stress?

Stomata are the pores on plant leaves that exchange gases with the environment. When a plant is stressed, such as by drought, it closes its stomata to conserve water.

What experiment is conducted to test if plants can eavesdrop on the stress of their neighbors?

The experiment involves cutting the roots of plants so that they share a common pot, allowing them to communicate through their roots. One plant is stressed, and the response of the neighboring plant is observed.

How do researchers measure the plant's response to stress in the experiment?

Researchers measure the opening and closing of stomata on the leaves of the plants as an indicator of their response to stress.

What does the script suggest about the communication between plants in terms of stress signals?

The script suggests that not only stressed plants send out signals, but also unstressed neighbors can relay these signals to even more distant plants, indicating a form of collective awareness.

How does the script demonstrate that plants can learn from past experiences?

The script describes an experiment where plants that have previously been exposed to a stressed neighbor show better resistance to drought, suggesting they have learned and remembered the experience.

What is the significance of the research findings in the script for our understanding of plant behavior?

The research findings highlight that plants, despite lacking a brain, can exhibit complex behaviors such as communication, learning, and memory, which are crucial for their survival.

Who are the members of the lab mentioned in the script and what is their contribution?

The members of the lab are Dr. Omer Falik, Ishay Hoffman, Yonat Mordoch, Daniel Ben-Natan Sion, Miri Vanunu, and Oron Goldstein. They contributed to overseeing the process and conducting most of the experiments.

Outlines

00:00

🌳 Plant Communication and Eavesdropping

The script introduces the topic of plant communication, questioning the philosophical conundrum of sound in a deserted forest and using it as a segue to discuss how plants interact with their environment. The speaker explains that while plants are traditionally thought to be silent, they actually communicate with each other and other organisms. This communication can be through attracting pollinators with flowers or ensuring seed dispersal through fruits. The main focus is on the plant's ability to communicate stress and danger to neighboring plants, which can then prepare for potential threats, a phenomenon referred to as 'talking trees'.

05:03

🔍 Experimenting with Plant Communication

This paragraph delves into the experimental process of studying plant communication. The speaker describes a method where plants are grown with shared roots, allowing them to potentially communicate with each other. The experiment involves stressing one plant and observing if the neighboring plant responds, suggesting a form of eavesdropping on stress signals. The response is measured through the opening and closing of stomata, the pores on plant leaves that facilitate gas exchange. The speaker highlights the rapid response of stomata as a key physiological indicator of plant stress and communication.

10:04

🌿 Dissecting the Mechanism of Plant Communication

The speaker continues to explore the concept of plant communication, focusing on the mechanisms behind it. They propose that not only stressed plants share information, but also unstressed neighbors relay the stress signals to even more distant plants. This is demonstrated through an experiment where multiple plants are connected and the propagation of stress signals is observed. The speaker also addresses the question of how this communication occurs, distinguishing between above-ground volatile chemical signals and below-ground root communication, with the latter being confirmed as the primary method in their experiments.

15:08

📚 Learning from Experience: Plant Memory and Adaptation

In the final paragraph, the speaker discusses the implications of their findings on plant communication for survival and adaptation. They suggest that plants can learn from past experiences with stress, such as drought, and use this information to better withstand future hardships. The experiment involves pre-stressing one plant in a row of plants sharing roots and then subjecting the entire setup to drought conditions. The results indicate that plants with prior communicative experience of stress are better able to survive real-life stress situations, demonstrating a form of learning and memory in plants. The speaker concludes by acknowledging the contributions of their lab members and the financial support from the Israel Science Foundation.

Keywords

💡Plant Communication

Plant Communication refers to the various ways in which plants interact and exchange signals with each other and their environment. In the video, this concept is central as it discusses how plants can 'talk' to each other, especially in response to stress or danger, such as when a tree falls in a forest. The script provides examples of plants releasing volatile chemicals as a form of distress signal, which can be detected by neighboring plants, prompting them to produce toxins to deter potential threats.

💡Stomata

Stomata are tiny pores found on the surface of plant leaves, which are responsible for gas exchange, allowing the plant to absorb carbon dioxide and release oxygen. The video explains that stomata can rapidly open and close in response to environmental stressors, such as drought. The script describes an experiment where the closing of stomata is used as a measurable response to demonstrate plant communication about stress.

💡Volatile Chemicals

Volatile chemicals are substances that easily become airborne and can be detected by organisms at a distance. In the context of the video, these chemicals are released by plants as a means of communication, particularly when they are under attack or stress. The script mentions that plants can emit these chemicals to warn neighboring plants of potential threats, such as insect attacks.

💡Eavesdropping

In the video, 'eavesdropping' is used metaphorically to describe the ability of plants to 'listen' to the stress signals of their neighbors and respond accordingly. The script discusses a study where plants are observed to react to the stress of nearby plants, even if they themselves have not experienced the stressor, suggesting a form of collective awareness among plants.

💡Stress Signals

Stress signals in the video refer to the various cues or messages that plants send out when they are under stress, such as from drought or insect attacks. These signals can be chemical or physical and are used to alert other plants to the potential threat. The script provides an example of how plants can close their stomata in response to stress signals, which is then observed in neighboring plants.

💡Root Communication

Root communication is a method by which plants can exchange information through their root systems. The video script describes an experiment where plants are grown in a way that allows their roots to interact, demonstrating that stress signals can be transmitted from one plant to another through this underground network.

💡Drought

Drought is a form of environmental stress characterized by a lack of water. In the video, drought is used as an example of a stressor that plants can prepare for by communicating with each other. The script explains that plants can 'learn' from the experience of a neighboring plant that has been exposed to drought and use this information to better withstand future drought conditions.

💡Learning and Memory

While typically associated with organisms that have a nervous system, the video script uses the terms 'learning' and 'memory' to describe the ability of plants to adapt their behavior based on past experiences. For example, plants that have been exposed to the stress signals of a drought-stressed neighbor can 'remember' this experience and exhibit a more resilient response to actual drought conditions in the future.

💡Clonal Plants

Clonal plants are those that reproduce asexually, often resulting in a group of genetically identical individuals. The video script mentions clonal plants as an example of how plants can be large and interconnected, which may explain why they share stress signals with their 'twin' parts, as a form of self-preservation.

💡Environmental Information

Environmental information in the context of the video refers to the cues and signals that plants use to understand and respond to their surroundings. The script discusses how plants can use this information to prepare for and adapt to various stressors, such as drought or insect attacks, by communicating with each other and 'eavesdropping' on the experiences of their neighbors.

💡Survivorship

Survivorship in the video is the ability of an organism to survive and thrive in its environment, especially in the face of challenges or stressors. The script emphasizes that plants, despite lacking a brain, can exhibit sophisticated behaviors that enhance their survivorship, such as communicating about stress and learning from past experiences.

Highlights

The profound philosophical question of whether a falling tree in an uninhabited forest makes a sound has intrigued philosophers for over 300 years.

Plants communicate with each other and their environment, a concept that may seem ridiculous to neighboring plants but is a significant part of their existence.

Plants use flashy flowers to attract pollinators, a form of communication crucial for their reproductive process.

Plants also communicate by producing flashy fruits filled with sweet rewards to encourage seed dispersal by animals.

The concept of 'talking trees' where trees can warn each other of threats through chemical signals is introduced.

Plants can produce toxins and odors when under attack, signaling nearby plants to prepare their own defenses.

Researchers are investigating if plants can eavesdrop on the stress signals of their neighbors to better resist future threats.

A simple method using seedlings and scissors to test plant communication through shared roots is described.

Plants' stomata, the pores on leaves for gas exchange, can be used as a measurable indicator of stress response.

Stressed plants close their stomata, while unstressed plants remain open, and this response can be visually measured.

Unstressed neighboring plants can sense stress in others and respond by closing their stomata, indicating communication between them.

Plants can share stress information with multiple neighbors, even without direct stress themselves.

Root communication is proven as the primary method of stress signal transmission between plants.

Plants can learn from past experiences with stress and use this knowledge to better survive future hardships.

The experiment demonstrates that plants can remember and adapt to drought conditions based on communicated stress signals.

The presentation concludes with a lesson on how even brainless creatures can learn, memorize, and use environmental information for survival.

The importance of understanding plant communication for ecological and evolutionary insights is emphasized.

Transcripts

Transcriber: Sándor Nagy Reviewer: Capa Girl

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 a 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 [who] 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? (Laughter)

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 seed[ling]s

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 draught -

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 on 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!

(Applause)