Talking to: Prof. Daniel Chamovitz, 53, U.S.-born expert on plant genetics, dean of the Faculty of Life Sciences at Tel Aviv University; married, lives in Hod Hasharon. Known for: His book, ‘What a Plant Knows’ (2012; in English). Where: His office at TAU. When: Thursday, 11 A.M.
I have a potted palm plant in my study and we spend a lot of time together. What does it know about me?
It doesn’t give two hoots about you.
Too bad. Does it know the color of my shirt, for example?
It knows whether the shirt you’re wearing is blue or red.
Does it know whether I’m in the room?
It knows that its surroundings change. If you stand above it, it knows you are preventing it from receiving light.
But does it know whether I’m a person or a mouse or tree?
It knows the nature of the entity standing above it. Let’s say, it knows whether it’s a plant, according to the light that passes through the leaf.
Does it have habits? For example, if I water it every day at 3 o’clock, does it come to expect that?
Plants have an internal clock, a circadian clock, just like ours. There are some plants, such as mimosa pudica – the “sensitive plant” [a member of the pea family] – that open their leaves during the day and close them at night. If I place a plant like that in total darkness or in bright light all the time, it will still preserve the same rhythm. If I place it in a plant-growth chamber and reverse its clock, it will undergo a few days of something like jet lag, in which it will open its leaves at night instead of during daytime. But after a few days, it will resynchronize. I don’t know for certain whether the plant “knows” it’s watered every day at 3, and I imagine it also depends on the type of plant. But intuitively, I believe that it does. It knows the light is turned on at a certain hour – there’s no doubt about that.
What are the plants doing, so innocent and silent in the window box?
Plants have all the senses that animals do, apart from hearing. They react to light, they know whether it’s night or day, they can smell. They react to touch or to breezes, they taste the soil, the water and the chemicals, they remember events – and, most important, they can integrate. Plants receive information from their roots, branches and flowers, and from their surroundings. And with their senses, they integrate all this information in order to produce something that is well suited to the specific environment of that moment. That integration is done without a brain.
What do you mean when you say they remember events?
They have the ability to remember environmental events and to adapt biology in order to be ready for those events in the future. We have an immune system. When we get a vaccination, or when we contract certain diseases, the body remembers that – and when we encounter that bacteria or virus again, there is an immediate immune reaction.
Like some diseases, which you only get once.
Right. Plants, too, have a similar type of memory, which enables them to adapt themselves to the future. Furthermore, they can teach their offspring. The seeds of a plant that undergoes water stress in a drought will be more resistant to drought than the seeds of a plant that didn’t endure drought. That’s a form of learning. Learning is also demonstrated by the Venus flytrap: If you touch it multiple times continuously, it will no longer bother to spring the trap – as though it “understands” someone is pulling a fast one, and it doesn’t want to waste energy.
Actually, I flinch from using the terms “learning” or “intelligence” in this context. I prefer to speak in terms of complexity. Plants possess enormous complexity and a tremendous range of reactions. We know, for example, that a branch senses the force of gravity and aspires to grow upward. But if a branch above it casts a shadow on it, the lower branch will incline sideways, toward the light. It chooses the optimal path for survival.
Can we talk about that in terms of a decision?
I think we can.
In your book, you mention dodder (cuscuta), a parasitic plant that prefers to attach itself to tomatoes rather than wheat. Is that also a decision – it smells both and understands which it prefers?
Yes, you can say “understands,” because the tomato emits a vaporous substance that strongly attracts dodder, while wheat emits a substance that repels it. As far as it’s concerned, the wheat simply stinks. In humans, too, the sense of smell allows us to know what we want. The smell of spoiled food repels us; the smell of fresh food attracts us. And it’s the same here – one plant attracts dodder, the other repels it.
And it chooses between the two options.
Yes. It doesn’t know this is a tomato and this is wheat, but it happens. There’s an amazing clip on YouTube showing dodder simply turning right toward a tomato.
So some plants are more sophisticated than others.
The Venus flytrap, for example, has a system comparable to a nervous system that allows it to know when to close.
Not only when to close, but also when a fly lands on it or when it’s, say, a leaf from a neighboring plant.
Exactly. It can make the distinction. Other plants also have this ability to discern. They know when to perform photosynthesis according to the amount of light they receive. We perceive plants as simple entities, but in principle they are more sophisticated even than animals, because they are immobile. That immobility effectively dictates their whole biology.
A plant cannot escape.
Right. The solution of animals and people to a threatening environment is to escape. A plant doesn’t have that privilege, it’s rooted in the soil. If it’s growing in the northern United States, for example, it has to survive temperatures of 40 degrees Celsius in the summer and minus 40 degrees in the winter; also drought, floods, winds, epidemics, pests. If it doesn’t know how to sense the environment and adapt itself biologically, it will die. Its responses are, therefore, far more sophisticated. It even “knows” whether the tree next to it is being attacked by pests. The adjacent tree emits a vaporous substance into the air that the other tree smells and reacts to. One can argue whether this is communication as we define it, but it is certainly an exchange of information – information that causes the tree to alter its physiology in order to survive.
The changes you’re talking about are very gradual, aren’t they?
They are gradual from our perspective, but biologically, genetically, they are very rapid reactions. When a plant withers in a way that is apparent to the eye, that is already a very advanced stage in the process of its reaction to drought. We simply don’t see the reactions that preceded it. That’s our big problem with plants: We just don’t see what they’re doing.
What do you mean?
If we put a new plant on the windowsill, after a day or two we will see it inclining toward the light. With time-lapse photography, we would see it moving and bending. In contrast to the action of the Venus flytrap, whose motion we understand because it’s similar to what we do when we try to catch a fly on our wrist – most plant movements are very slow. It’s like the “Star Trek” episode when they come to a place where time seems to slow down and no one moves. But it hasn’t slowed down, it’s just different from the time in their world.
Can plants communicate?
They exchange information. A study published by Prof. Ariel Novoplansky from Ben-Gurion University showed that if a plant finds itself in dry ground, its roots emit a certain substance that is picked up by the roots of the adjacent plant. And even if the latter is in moist soil, it will start to protect itself, knowing that dryness is coming.
What interest does a plant have in helping another plant survive?
There are two possibilities. One is that this is a phenomenon of altruism in evolution – if the whole population takes protective measures simultaneously, that is good for the individual. The second is that if a specific branch, say, is attacked by aphids and wants to “warn” its brother branch, the fastest way to communicate is with these vaporous substances.
Many plants are dependent on insects to survive, so is there communication between plants and insects?
Yes. For example, when corn is attacked by a certain type of worm, it emits an odor in the air that attracts aggressive hornets, which eat the worms. Of course, it’s not that the plant is saying, “How awful, I’m being eaten, I’ll go get the hornets.” What probably happens, in evolutionary terms, is that when the plant is being eaten, a certain substance is emitted and the hornet has learned that its odor signals the presence of worms nearby. Communication exists.
What about plants’ feelings? What do they feel when they’re touched, when they’re cut?
Plants sense touch, but it doesn’t hurt them. They don’t have a sense of pain. Pain is subjective, the result of complex processes in the brain’s prefrontal cortex. Plants possess neither subjectivity nor a brain. And they don’t have specific pain sensors, as people do. There are also plants that want us to eat them, because that’s how they scatter their seeds. They wouldn’t want us to eat them if it hurt.
So plants have perhaps not sentient existence but a conscious existence.
Yes. For most people, plants aren’t much different from stones. That’s not so. In terms of awareness or complexity, it’s simply a different evolutionary adaptation for survival.
Maybe they’re like science-fiction aliens?
It’s not by chance that we arrive at science fiction. Plants are so different from us that we are simply incapable of identifying with them. As human beings, we tend to use the definition “us” versus “them.” We define and differentiate. Plants are truly “them.” I’ve been asked several times whether plants will one day learn to talk like us. The answer, of course, is no. Why? Because they don’t need to. It’s a completely different evolutionary line. We think humanity is the apex of evolution, but that’s not true. We are simply one solution of evolution.
We’re an option.
Yes, and not necessarily the best option. But we are definitely the only option that is capable of asking itself questions like these ... You can say that in a particular period this gave us an advantage, and therefore we survived and developed. Will we continue to survive and develop for another 400,000 years? That’s far from sure. But plants? I’m sure they will. There are more than 200,000 types of plants, and they are capable of adapting very rapidly to the environment. A study I was involved in on climate change found that, within 10 years, the plants that were examined altered themselves physiologically to adjust to the new climatic conditions.
So what can we learn from plants?
A great deal. To begin with, we learned the basic laws of genetics from studying plants – [19th-century geneticist] Gregor Mendel worked with pea plants. Much of our current understanding of molecular genetics is based on the study of plants. My personal research dealt with a group of genes that allows a plant to “know” whether it’s in light or darkness, and how it copes with the surroundings. It turned out that the genes I discovered, which I had thought unique to flora, are also found in people. Conversely, genes we thought were human – such as a BRCA mutation, which leads to breast cancer – exist in plants, too. After many years of research, I discovered that not only do plants and humans share genes, but plants also produce chemicals that affect people in the form of medicines. I started to ask myself why the broccoli plant creates substances that appear to help prevent cancer.
Not because broccoli is fond of us, I imagine.
Right, there’s nothing to thank it for. But if you place that substance on a plant in the lab, its cells stop dividing – exactly what we want to happen in cancer medicines. The plant uses it to regulate its growth. In the past year, we discovered that when the plant is eaten by an insect, it produces this substance and stops cell division; in other words, it stops growing in order to be able to defend itself against the insect. When the insect leaves, the plant resumes its growth. And when we eat that chemical, it influences us in a similar manner: The cells stop dividing. It’s amazing. That doesn’t mean cancer patients should forsake medical treatment and start eating broccoli, but a huge portion of our medicines originate in plants. Plants contain substances that can influence our brain.
Why is that?
Plants don’t have neurons, but they need to communicate between cells. Communication between neurons in people, and between cells in plants, is mediated by chemicals, neurotransmitters. Plants have a chemical that regulates their neurotransmitters, so if we eat it, it will regulate our neurotransmitters. The transmission of information in a plant is mediated by a neurotransmitter, without a brain and without neurons.
It’s like a beta version of a mammalian brain.
It’s not necessarily that one developed from the other; there was something in common very early on, then there was a split. Intercellular communication was required in the primal cells.
So even our brain is a kind of variation on that communication.
That’s the point. What we find most difficult to understand is that the nervous system and brain are indeed an amazing evolutionary solution for processing information.
But not the only solution.
Exactly. It’s one variation that was suitable for us, and that also causes us multiple neuroses. Maybe the plants’ solution is better, because they don’t have neuroses.
Look, what’s the only thing that really distinguishes us from the plants? Both plants and humans see, are able to smell, feel, react, have memories and want their offspring to flourish – but only we care. Plants are like Rhett Butler, who does everything the same way, but frankly my dear, he doesn’t give a damn.
You say in the book that, genetically, plants are more complex than humans.
Yes, that’s a fact. Some plants have more genes than humans do.
Why do they need so many genes?
It’s a survival advantage. Take photoreceptors, for example. Our retina has four genes for photoreceptors, whereas a plant has more than 13. They have a gene for strong red light, another for red light of medium strength, another that reacts only to very low strength, and more. A plant must have the ability to adapt itself to its surroundings at all times.
To what extent are we part of the surroundings to which plants adapt themselves? It seems to connect with the theories of Yuval Noah Harari, who claims that wheat domesticated us.
It’s not a matter of will; wheat did not domesticate us. In evolution, the goal of each being is to possess the ability to survive and pass their genes along. Wheat conquered the world, but it’s dependent on us for its survival. If human beings become extinct, wheat and dogs will not survive.
Has your perception of reality changed in the wake of the knowledge you’ve gleaned from plants?
I am not religiously observant and I don’t believe in mysticism – and I don’t want to sound like someone who is – but understanding the resemblance between plants and animals affords me a very deep appreciation of the unity of nature. The fact that biological principles, mechanisms and genes are shared by roses and Homo sapiens helps me appreciate how amazing evolution is, and at the philosophical level to ask what defines a human being.
Why did you become interested in plants?
In 1982, I did a year of national service in Kibbutz Ketura [in the Arava Desert], driving a tractor in alfalfa fields. Like every Jewish-American kid whose father is a doctor, I was certain that I too would be a doctor. I didn’t know anything about agriculture or plants, but noticed that alfalfa grew back when it was cut but wheat didn’t. I said to myself that if we could understand why alfalfa grew back and somehow introduce that trait into wheat, we could feed the world.
Think about it: We wear plants, we drink and eat plants, we’re both sitting on plants, we take medicines made from plants, and the oxygen we breathe is a plant product. In fact, our life is completely dependent on plants. Plants can get along without us, but we are dependent on them and yet take them for granted. As a society, we have lost the plants.
What do you mean?
We think there’s no need to learn about them. We prefer cancer research and brain research. But if we don’t teach about plants and study them on the same scale as cancer and brain research, we will find ourselves in serious trouble. There were three billion people on the planet the year I was born; now there are already seven billion.
With an expectancy of nine billion by 2050.
Right, and the more people there are, the less available land there is for farming. How will we have enough food in 2050, in a constantly changing climate? The existing agriculture, which fed the world at the price of tremendous environmental damage, is unsustainable. If we don’t understand how plants sense their surroundings and react, or go through adaptations, and then assimilate that knowledge into agriculture, we will face a huge problem. In China, almost 50 percent of the government’s research budget is earmarked for the plant sciences, because they understand their immense importance. But here it’s not considered sexy enough. In 2003, I welcomed the completion of the Human Genome Project, but its crucial aspect for me was that we now had the technological tools to decode the plant genome.
With all due respect to cancer and Alzheimer’s – diseases with which I am well acquainted, unfortunately – most people in the world don’t care about either of them, because they don’t even reach the relevant age. They simply want to eat.