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

A decrease in electric resistance and an increase in the extracellularCl^– concentration ([Cl^–]) in the main pulvinus ofMimosa occurred immediately after the action potential of themotor cells. The beginnings of both changes were almost coincidentalwith the beginning of the rapid movement. A remarkable increasein [Cl^–] was seen in the lower half of the pulvinus, butonly a slight increase in the upper half. Release of Cl^–,probably with K⁺; and other ions, from the motor cells impliesan ejection of liquid from the vacuole. When recovery of thepulvinus following rapid movement was fast in light, [Cl^–]decreased to its initial level within 20 min. When the recoverywas slow in darkness, [Cl^–] decreased at a slow rate andmaintained a higher level than its initial one for a long time.Photosynthetic inhibitors delayed recovery and the decreasein [Cl^–] even in light. These facts suggest that the re-entryof ions into motor cells during recovery partially requiresa photosynthetic energy supply. (Received February 12, 1980; )