Venus flytrap snaps shut by softening outer cell walls in about one second, Science study finds
Aix-Marseille University and CNRS researchers found that closure is too fast for water transport: the outer cell wall softens and releases stored elastic energy.
A team from Aix-Marseille University and CNRS in France, including Jeongeun Ryu and Yoël Forterre, has identified what drives the fast closing of the Venus flytrap (Dionaea muscipula) trap, according to a study in Science. Closure occurs too quickly to be explained by water transport. Instead, the epidermal cell wall softens in about one second and releases elastic energy stored in the trap science.org
Sciencescience.orgOpen source ↗. The authors describe this as the fastest modulation of wall mechanics reported in plants.
Why water is too slow
Each trap is a leaf with two lobes joined along a central rib. Open lobes curve outward and closed lobes curve inward, and the switch is sudden, like an umbrella flipping in a gust. In an uncut trap, the flip itself takes about a fifth of a second. In 11 traps sliced into strips, which can bend but cannot snap, closure took about 3 seconds.
The earlier explanation held that water moves across the leaf and bends the lobes. The team measured pressure in 14 leaf cells and found that water needs about 3.7 seconds to pass through one cell. The leaf is about 0.5 mm thick, and water would cross 5 to 10 cell layers, which by the team's calculation takes 30 to 150 seconds. In a second test, with 48 strips from six traps, water needed 38 seconds on average to cross the leaf. The lobes bend in 3 to 4 seconds.
Softening of the outer wall
Using a fine probe on single cells in 10 traps, the researchers measured stiffness before and after triggering. Cells of the inner layer changed little. Cells of the outer layer lost nearly a third of their stiffness and stayed softer for at least an hour. A single touch, which does not close the trap, did not soften them science.org
Sciencescience.orgOpen source ↗.
In five traps held almost still, the outer cells softened within seconds of triggering, about as fast as the lobes bend. Molds of the outer surface of five traps showed cells bulging about 8% more after triggering, which the team took as evidence that the walls softened rather than lost pressure. Simulations of a single cell gave a loss of roughly 30% to 40% of wall stiffness.
The cause of the softening is not yet known. Calcium is one candidate, but the authors say its role may be indirect. The probe mainly detects elastic changes, and water movement over shorter distances is not ruled out. The authors suggest the principle could inform soft robots with parts that change stiffness; no device was built or tested.
