Rhythmic leaf movements: Physiological and molecular aspects

Daily periodic plant leaf movements, known since antiquity, are dramatic manifestations of "osmotic motors" regulated by the endogenous biological clock and by light, perceived by phytochrome and, possibly, by phototropins. Both the reversible movements and their regulation usually occur in specialized motor leaf organs, pulvini. The movements result from opposing volume changes in two oppositely positioned parts of the pulvinus. Water fluxes into the motor cells in the swelling part and out of the motor cells in the concomitantly shrinking part are powered by ion fluxes into and out of these cells, and all of these fluxes occur through tightly regulated membranal proteins: pumps, carriers, and ion and water channels. This chapter attempts to piece together those findings and insights about this mechanism which have accumulated during the past one and a half decades.