Mechanism of the Seismonastic Reaction in Mimosa pudica.

The efflux of K(+) from the pulvinar cells of Mimosa pudica was shown to increase substantially during the seismonastic reaction. This result is shown to indicate a decrease in sigma (reflection coefficient) of pulvinar cell membrane for potassium salts which could account for the pulvinar cell turgor decrease during the seismonastic reaction.Membrane potentials and concentrations of Ca(2+), K(+), Cl(-), S, and P were measured in the top and bottom halves of pulvini. Pulvinar cells showed a large negative membrane potential, cell vacuole relative to external solution, but no significant difference in membrane potential could be detected between upper and lower pulvinar cells. A large difference in K(+) and Cl(-) concentration between top and bottom pulvinar halves was evident in reactive pulvini but not in unreactive pulvini. The effect of K(+) concentration on plant growth and leaf reactivity was also investigated.