No Brainer Behavior: Messages, Memory, Maybe Even Intelligence-Botanists Wrangle over How Far Plants Can Go

Article excerpt

In a somewhat different world, Consuelo M. De Moraes would be revolutionizing vampire fiction. Her lab at Penn State University studies predators that entangle prey in a tight embrace, pierce victims' tissue and suck out nourishment. In the last few years, De Moraes and her colleagues have found that the predators even hunt down prey by scent.

Creepy as her predator, Cuscuta pentagona, is, it is also, frankly, a plant. Better known as five-angled dodder, its orange tentacles bypass the porcelain throats of young women in favor of the slim stems of young tomato plants. De Moraes and other researchers are showing that plants behave and misbehave as dramatically as animals. But there's still not much hope for a feature-length dodder movie.

"I think most people regard plants as being pretty unresponsive and stuck in one place," laments ecologist Richard Karban of the University of California, Davis. "Now, animals, they're interesting because they can change and act in response to their environment."

It's a dichotomy Karban doesn't accept for one second. When he and an animal behaviorist recently supervised a grad student, he remembers, "I would constantly want to say, 'Oh yeah! Yeah! Plants do that too!'" Recent findings on plant capacities, he declares in a 2008 paper in Ecology Letters, reveal "high levels of sophistication previously thought to be within the sole domain of animal behavior."

Even plants less vampirish than Cuscuta vines forage strategically for their food, and there's evidence that plants fight each other over resources. In abroad sense of the word, plants communicate--some essentially scream for help. Also, a plant can respond to stimuli depending on its history of previous experiences, a tendency Karban is willing to call a sign of memory.

Karban stops there, but other plant scientists go much further in borrowing animal terminology. In May, researchers gathered in Florence, Italy, for their fifth annual meeting on "plant neurobiology," and some of these green neuroscientists talk about searching for a plant "brain." The June issue of Plant, Cell & Environment, devoted to plant behavior, even begins with a paper that uses the term "plant intelligence."

Expanding the language for describing plants to include at least some "behavior" words could expand ideas for research, Karban contends. Plant researchers might do well to borrow analytic techniques from animal scientists, he adds. Finally, everyone may discover just how exciting it can be to watch grass grow.

Movement in animal time

One of the first questions posed to believers in plant behavior is, "How can plants behave if they can't move?"

Part one of plant behaviorists' almost universal answer: Plants do move.

Time-lapse photography of growing shoots reveals spooky, circular sweeps called nutation. The circular motion arises because a shoot does not necessarily grow evenly, with cells on one side elongating as fast as cells on the other. Growth rate varies on different sides. Over hours or days, the growing tip moves like a turning searchlight.

And as plant scientists relish pointing out, some plants do move in animal time, especially those that hunt animals for food. When it lands inside the open jaws of a Venus flytrap, a fly may jog trigger hairs. An electrical signal zaps through the plant tissue and the two sides of the trap can close like a book in less than a second. And a water flea that bumbles into a little cup of a bladderwort likewise confronts the peril of touch-sensitive triggers. A trapdoor opens within 30 milliseconds, and the flea whooshes down into a digestive chamber.

No insects are harmed when white mulberry trees bloom, but the Morus alba flowers open with a quick puff of yellow pollen. In a lab setup, a team of aerosol specialists at Caltech found the mulberry flower's parts moving at speeds exceeding Mach 0.5. …