Changes in the extracellular ion concentration in the main pulvinus of <italic>Mimosa pudica</italic> during rapid movement and recovery

Abstract

A decrease in electric resistance and an increase in the extracellular Cl− concentration ([Cl−]) in the main pulvinus of Mimosa occurred immediately after the action potential of the motor cells. The beginnings of both changes were almost coincidental with the beginning of the rapid movement. A remarkable increase in [Cl−] was seen in the lower half of the pulvinus, but only a slight increase in the upper half. Release of Cl−, probably with K+; and other ions, from the motor cells implies an ejection of liquid from the vacuole. When recovery of the pulvinus following rapid movement was fast in light, [Cl−] decreased to its initial level within 20 min. When the recovery was slow in darkness, [Cl−] decreased at a slow rate and maintained a higher level than its initial one for a long time. Photosynthetic inhibitors delayed recovery and the decrease in [Cl−] even in light. These facts suggest that the re-entry of ions into motor cells during recovery partially requires a photosynthetic energy supply.