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Summer 2006

There’s a buzz in the world of botanical science. Led by Anthony Trewavas, a highly-regarded scientist at the University of Edinburgh and a member of Great Britain’s Royal Academy, researchers all over the world are suggesting that plants are more than a leafy backdrop for Earth’s more active and interesting residents. The buzz is that plants communicate. They plan ahead. They remember. They’re intelligent.

Are we on the brink of a revolution in biological thought? That depends.

Washington State University psychologist Jay Wright, who studies learning and memory in mammals, wonders what it means to say that a plant is intelligent. Even with respect to animals, he says, “intelligence is in the eye of the beholder.”

When sizing up smarts, we often look for intentional actions, goal-directed behaviors we can see and measure. How can plants be intelligent? To the casual observer, plants don’t seem to have “behaviors.” They seem to passively accept whatever the environment tosses their way.

But researchers at WSU are finding that plants are surprisingly assertive. Based on their findings, a case could be made that the average potted plant is at least as active as the average human couch potato—and a lot smarter about what it consumes and the company it keeps.

Watching their diet

Plants don’t “eat,” of course, but they do take in energy, in the form of light. They use that energy to convert CO₂ and water into carbohydrates. Although plants can’t move to a sunnier or shadier spot like a sunbather going for optimal tan, plant physiologist David Kramer says some of them make smaller movements to control their exposure to light. They turn their leaves to intercept more or less light. They even rearrange their internal parts to enhance or diminish their energy intake.

In fact, says Kramer, leaves are so active that they have made it nearly impossible to do certain kinds of experiments for longer than a fraction of a second. For example, when scientists directed narrow beams of light at leaves in order to track changes in the chemicals involved in photosynthetic reactions, the leaves reacted about the same way you or I would to having a bright light shone in our faces. Ultra-short experiments worked fine, but anyone wanting to watch what happened over a span of minutes was out of luck.

“The plants were moving,” Kramer says. “They could change the shape of their cells and the chloroplasts, and that scatters the light differently. That’s a problem.”

His solution was to invent an instrument that scrambles the light before it hits the leaf and efficiently collects the scattered light that comes out the other side. With this machine, movements within the leaf have little effect on the measurements, because the light is already scattered.

Kramer dubbed the instrument Nofospec, for “non-focusing optics flash spectrophotometer,” and patented it. Besides the one in his own lab, he has made a Nofospec for colleagues at WSU and the University of California-Davis, and has orders for more from labs in Japan and France.

Kramer says plants have another, even more subtle, way to control how much light energy they feed into the photosynthetic pathway. In weak light, they are incredibly efficient. Their light-gathering apparatus, highly organized protein clusters called antennae, send about 80 percent of the photons striking them into growth and maintenance activities.

In bright light, though, they pull the shades. Instead of funneling the light energy into the photosynthetic reactions, the antennae send up to 90 percent of it back out into the environment as heat.

They have to do that, says Kramer, or risk being bleached and burned by the intense energy concentrated in their chloroplasts.

“Basically, the plants are dealing with explosives,” he says. “They need to, to drive all these [photosynthetic] reactions—but if they take in too much, they’re going to pay the consequences.”

His group is studying how the plant knows to turn its antennae up or down. “People spent decades trying to improve the efficiency of photosynthesis,” he says. “And plants are already pretty damn good at it. The key here is matching the regulation to the environment.”

And plants are masters at that. They monitor the light striking every bit of leaf surface, and act in a way that takes into account both their need for energy and the risks of overindulgence.

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Continued

As shown in the images below, people in the Middle Ages thought plants had abilities that paralleled those of humans and animals. WSU psychologist Jay Wright says the idea of plant intelligence is intriguing, but it's not new. "It's cyclical," he says, citing a flush of "smart plant" research in the 1920s and again in the 50s and 60s. Those efforts sputtered out for lack of solid evidence. New research into how plants communicate and manage their environment puts the notion on more solid footing today.  Images are from the Italian Herbal, Special Collections, University of Vermont Library.