Vacuolar reorganization in the motor cells of Albizzia during leaf movement.

During the leaf movements of Albizzia julibrissin Durazzini, volume changes in the motor cells of the pulvinule (tertiary pulvinus) are closely correlated with a reversible reorganization of the vacuolar compartment. Motor cells have central vacuoles when expanded, but become multivacuolate during the time the cell volume decreases. The central vacuole reforms - apparently by fusion of small vacuoles - during motor-cell expansion. The volume changes of the vacuolar compartment account for all of the change in the size of the protoplast, while the cytoplasmic volume remains constant during the leaf movements.