Jan. 28, 2005 A team of researchers has solved the riddle of one of the plant kingdom's fastest and most ferocious movements: the blink-of-an-eye closing of the Venus flytrap.
While "speed" is not a word most people associate with the plant kingdom, the Venus flytrap closes its v-shaped leaves in just one-tenth of a second - fast enough to accomplish a feat thousands if not millions of backyard barbecuers fail at each summer: snaring a fly.
So how can a plant pull this off?
By storing and releasing elastic energy, according to Gordon McKay Professor of Applied Mathematics and Mechanics Lakshminarayanan Mahadevan.
Mahadevan likened the Venus flytrap's hinged leaves to a plastic lid that is bowed in one direction and then suddenly pops the other way. While waiting for prey, the plant's leaves are bowed outward, opening the hinged trap. When an insect touches the hairy triggers located inside of the trap, the plant moves water in the leaves, changing their curvature and suddenly snapping them closed.
"It is a relatively simple mechanism, but the plant is actively controlling it," Mahadevan said.
The plant then excretes digestive enzymes that break down the meal, providing nutrients that the plant cannot get from the poor, boggy soil where it grows naturally.
The research, published in the Jan. 27 issue of the journal Nature, was conducted largely while Mahadevan was at the University of Cambridge before coming to Harvard in 2003. The work was prompted by a simple gift of a Venus flytrap to Mahadevan from one of the members of his research lab.
Mahadevan, whose expertise is understanding the mechanisms behind ordinary phenomena such as wrinkling sheets and rolling droplets, said that he'd been interested for years in how the flytrap was able to close its leaves so quickly without the benefit of either nerves or muscles.
With one sitting on his desk, that passive interest quickly turned active.
"We studied this because it is an extreme event. The very fact that it is a plant and it is moving fast was enough for us to want to study it," Mahadevan said.
Mahadevan gives plenty of credit to his colleagues on the project, who were all members of his Cambridge lab at the time, including Yoel Forterre, currently of the Universite de Provence, Jan M. Skotheim of Cambridge and of Harvard, and Jacques Dumais, now an assistant professor of organismic and evolutionary biology at Harvard.
To view how the flytrap works, the researchers painted ultraviolet fluorescent dots on the leaves and then filmed them under ultraviolet light using high-speed video. By breaking down the movements, they were able to reconstruct the geometry of the leaf and design a mathematical model to help them understand what was happening when it snapped closed.
Mahadevan said the group's interdisciplinary expertise, which included applied math to physics to biology, was critical for the project's success.
Though Mahadevan's work sheds light on the mechanical functioning of the flytrap's leaf, he said the molecular processes that drive the movement remain unexplained.
Though the workings of a familiar, but unusual plant such as the Venus flytrap seem a prime subject for scientific study, Mahadevan said he was not surprised to learn that it is poorly understood.
"Familiarity does not immediately mean comprehension," Mahadevan said.
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