Do Plants Think?

Daniel Chamowitz Image: Alan Chapelski

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How aware are plants? This is the central question behind a fascinating new book, ?What a Plant Knows,? by Daniel Chamovitz, director of the Manna Center for Plant Biosciences at Tel Aviv University. A plant, he argues, can see, smell and feel. It can mount a defense when under siege, and warn its neighbors of trouble on the way. A plant can even be said to have a memory. But does this mean that plants think ? or that one can speak of a ?neuroscience? of the flower? Chamovitz answered questions from Mind Matters editor Gareth Cook.

1. How did you first get interested in this topic?
My interest in the parallels between plant and human senses got their start when I was a young postdoctoral fellow in the laboratory of Xing-Wang Deng at Yale University in the mid 1990s. I was interested in studying a biological process that would be specific to plants, and would not be connected to human biology (probably as a response to the six other ?doctors? in my family, all of whom are physicians). So I was drawn to the question of how plants sense light to regulate their development.

It had been known for decades that plants use light not only for photosynthesis, but also as a signal that changes the way plants grow. In my research I discovered a unique group of genes necessary for a plant to determine if it?s in the light or in the dark. When we reported our findings, it appeared these genes were unique to the plant kingdom, which fit well with my desire to avoid any thing touching on human biology. But much to my surprise and against all of my plans, I later discovered that this same group of genes is also part of the human DNA.

This led to the obvious question as to what these seemingly ?plant-specific? genes do in people.? Many years later, we now know that these same genes are important in animals for the timing of cell division, the axonal growth of neurons, and the proper functioning of the immune system.

But most amazingly, these genes also regulate responses to light in animals! While we don?t change our form in response to light as plants do, we are affected by lab at the level of our internal clock. Our internal circadian clocks keep us on a 24 hour rhythm, which is why when we travel half way around the world we experience jet lag. But this clock can be reset by light. A few years ago I showed, in collaboration with Justin Blau at NYU, that mutant fruit flies that were missing some of these genes lost the ability to respond to light. In other words, if we changed their clocks, they remained in jetlag.

This led me to realize that the genetic difference between plants and animals is not as significant as I had once naively believed. So while not actively researching this field, I began to question the parallels between plant and human biology even as my own research evolved from studying plant responses to light to leukemia in fruit flies.

2. How do think people should change how they think about plants?
People have to realize that plants are complex organisms that live rich, sensual lives. You know many of us relate to plants as inanimate objects, not much different from stones. Even the fact that many people substitute silk flowers for real ones, or artificial Christmas trees for a live one, is exemplary at some level of how we relate to plants. You know, I don?t know anyone who keeps a stuffed dog in place of a real one!

But if we realize that all of plant biology arises from the evolutionary constriction of the ?rootedness? that keep plants immobile, then we can start to appreciate the very sophisticated biology going on in leaves and flowers. If you think about it, rootedness is a huge evolutionary constraint. It means that plants can?t escape a bad environment, can?t migrate in the search of food or a mate. So plants had to develop incredibly sensitive and complex sensory mechanisms that would let them survive in ever changing environments. I mean if you?re hungry or thirsty, you can walk to the nearest watering hole (or bar). If you?re hot, you can move north, if you?re looking for a mate, you can go out to a party. But plants are immobile. They need to see where their food is. They need to feel the weather, and they need to smell danger. And then they need to be able to integrate all of this very dynamic and changing information. Just because we don?t see plants moving doesn?t mean that there?s not a very rich and dynamic world going on inside the plant.

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