Biomechanics of fast actuation in Mimosa pudica

The "touch-me-not" plant, Mimosa pudica, folds its leaves in less than a second in response to mechanical or electrical stimuli. This movement is reversible, and the leaf snaps back into place within a few tens of minutes.

The rapid transport of water by osmosis within the pulvinus - a flexible, hinge-like bulge at the base of the leaf, acting as the motor organ - is the classic explanation for these movements. However, this scenario lacks experimental evidence. We first characterize the kinematics of the movement and the mechanics of the pulvinus using macroscopic measurements. We then propose a simple model based on an osmotic motor to capture the macroscopic dynamic. Finally, we propose an alternative mechanism based on local redistribution of water from cells to neighboring air cavities, rather than organ-wide water transport.