NATURE • VOL 338 • 30 MARCH 1989 • PP 427-430

Cytosolic calcium regulates ion channels in the plasma membrane of Vicia faba guard cells

Julian I. Schroeder & Susumu Hagiwara

Department of Physiology, Jerry Lewis Neuromuscular Research Center
UCLA School of Medicine, Los Angeles, California 90024, USA

The molecular mechanisms by which Ca2+ controls a variety of ion transport-associated cellular functions in higher plant cells, including movements of stomatal pores, remain unknown. Stomatal pores regulate the gas exchange in leaves. Openings of stomatal pores are mediated by an increase in the intracellular potassium and anion content of guard cells. Voltage-dependent K+ channels and hyperpolarizing H+ pumps have been identified as mechanisms controlling stomatal movements. But depolarizing mechanisms required for K+ efflux during stomatal closing remain unknown. Indirect evidence suggests that Ca2+ triggers stomatal closing and inhibits stomatal opening. Using patch-clamp techniques, we show here that elevated (micromolar) concentrations of cytosolic Ca2+ in guard cells block inward rectifying K+ channels. Furthermore, elevation of cytosolic Ca2+ leads to the activation of a voltage-dependent depolarizing conductance with a permeability to anions. The Ca2+ induced modulation of ion channels reported here could provide a molecular basis for Ca2+ dependent regulation of stomatal movements in leaves.