Plant intelligence: how do we measure it?

Canadian Museum of Nature explores concept of plant intelligence

The latest session of the Museum’s “Nature Talks” series of lectures was held Tuesday March 18. Topic? Globe and Mail science reporter Ivan Semeniuk interviewed Paul Sokoloff, a botany research assistant at the Museum, on the subject of plant intelligence. (Watch a video of this next week at nature.ca.)

Do plants “think”? Not as human beings do. However, Sokoloff said they possess something analogous.

“Electrical pathways are analogous to animals’ central nervous systems,” he said, “Of course, plants have no brain. But even though plants are stationary, they do a lot of what we often consider to be ‘intelligence’' They move in response to light. Roots detect gravity and send their shoots up through the soil to the sky.”

Among many other things, noted Sokoloff, plants detect humidity, minute changes in carbon dioxide, and soil PH. Of special interest to me was his claim that plants can resist being consumed by grazing animals because they can adapt chemically, to become less palatable. (Does this drive hybridization, I wonder, as we develop more tasty and nutritious grazing plants for beef and dairy cattle, for instance?)

During the conversation with Semeniuk, Sokoloff discussed plant memory and learning. He cited a researcher’s lab tests with Mimosa pudica (sensitive plant) where plants were repeatedly dropped. At first, as always happens when this species’ leaves are touched, they folded upon impact with the ground. However, after a while, they stopped doing so. The question is: Did these Mimosa plants learn to ignore stimuli which did not hurt them?

In a follow-up interview on Thursday March 20, I asked Sokoloff what types of chemicals plants use to successfully compete for space, light, and hence, survival.

“Black walnut trees emit a chemical called juglone which is released by their roots.” Insodoing, other plants cannot grow in soil adjacent to this species. In fact, Sokoloff told me, “Probably nothing much grows until the chemical is metabolized by the soil.” 

We don't normally think of plants polluting the soil... However, is this intelligence?  Thoughts? For more information, check Oxford Journals: Annals of Botany blog.