the intelligence of plants

When you brush a finger across a leaf, and the leaf curls up into a tight bundle, the leaf is responding visibly and directly to what might be a threat. Of the senses, touch is the most powerful and often underestimated system of communication. This holds true not only in humans and animals, but also in plants. By virtue of what looks to be inertia, plants are often considered to be unsophisticated. Closer inspection reveals that plants do in fact have a tremendous capacity to sense and respond to their environment. Over eons plants have developed complex methods of responding and adapting to environmental changes.

Some would go so far as to say that these responses are evidence of plant intelligence. The notion is controversial to say the least, but leading researchers in the field cite a wealth of evidence, from plants that can sense and trap insects for food, to the ability of plants to sense and deter predators by temporarily altering their chemistry. Controversy is fuelled not only by varying scientific opinions, but is also complicated by linguistic confusion over the precise definition of terms such as intelligence. Traditionalists would argue that an organism needs self-awareness for intelligence to be exhibited. But recent research into plants and their responses to events such as wounding have led some scientists to believe that, at least on a basic level, plants do indeed possess intelligence.

Plant neurobiology is a new, but rapidly growing field of research, which, explores the signalling and communication that occurs both between plants and between plants and other organisms. Professor Eric Davies of North Carolina State University spoke with us about science, space and the possibility that cellular phones could be our pesticides of the future.

There is skepticism, both within the sciences and with the general public, that surrounds the idea of plant intelligence. Is this science fiction and entertainment, rather than facts?

Plants are the basis of life on earth. They are what provide 99% of the photosynthesis that keeps everything else alive. Without plants there would be no humans. The reverse is not true. Because plants don’t go to the beach at the weekend or fly to Miami when it gets cold or put on a fur coat, people don’t realise that they have to survive in very hostile environments. Because plants can’t escape the environment, they have to be able to perceive it and then adapt to it very, very well.

It is hard to conceive of plants as being particularly sensitive organisms.

Plants are in fact capable of sensing things we can’t sense. They are smart. They use the only environmental factor that is constant to tell them which way to grow: gravity. Plants sense gravity and use it as their main directional force. When a seed germinates under ground it still has the stem growing up and the roots growing down, even though there is no light.

If plant intelligence were more readily accepted by the general public do you think issues such as global warming and environmental pollution would be taken more seriously? I wonder if we realise how sophisticated the landscape is that we are living in.

I think if more people had even a vague understanding of science we would be in a better place. In this country [America] a lot of people have difficulty accepting the science of evolution because they have a faith that does not let them believe in evolution. Faith and science are dealing with entirely different things.

Will we ever reach a point when we will accept that we have a lot to learn from plants? NASA, for instance, has contributed substantial funding to this area.

NASA knew that long-distance manned space travel means that you have got to grow plants. They are funding from a practical point of view. Plants are exquisitely sensitive to gravity, which is why experiments need to be done in space. Although NASA has been supporting this kind of research for a long time, I don’t know if that means they are more open-minded or if they are more realistic. They see it – the problem of life in space – as a problem that needs to be understood. There is a lot of science that has not yet been done which is hard to separate from science fiction.

Back on earth, are there examples of results from the research into plant intelligence that will begin to have an impact on the lives of the general population?

My research into how plants respond to wounding (which causes them to release their defence protein) shows that the same response can be triggered with a mild electric shock. So it may be possible to have electric wires running through the soil or the greenhouse, and instead of spraying with insecticides you might send this electric shock to cause the plants to start making their defence protein. Dr Alan Vian and a team of scientists at the Université Blaise Pascal in France have discovered that some plants are also capable of responding in this way to the equivalent of a ten-minute mobile phone call. It might be possible, instead of using an electrical charge, to zap them with cell phones to make them resistant to insects. I see understanding how plants perceive and respond to wounding, insects, and the cold as being especially helpful in the poorer parts of the world, where people can’t afford more fertilizer or water or pesticides to help make the plants more resistant.

It also seems to be a much more sustainable approach in the long term.

If you can get plants to protect themselves, then you don’t have to use insecticides, and this cuts down on the toxic compounds in the atmosphere. If the insects then chewed on the weeds rather than the plants we need, that could keep the weed population down, which would cut down on the amount of food, water and herbicide that needs to be applied. You would not have to spend vast amounts of money and chemicals on helping plants. Instead the plants would help and protect themselves.

Bloom (issue 16: 115-116)