Ca2+ and cell signalling in guard cells.
Abscisic acid (ABA)-induced stomatal closure involves two different signalling chains, only one of which is Ca(2+)-dependent. ABA induces deactivation of the inward K+ channel and activation of an inward 'background' current, changes also produced by high cytoplasmic Ca2+ or injection of inositol 1,4,5-trisphosphate. It is argued that ABA produces local increases in Ca2+, which are obligatory for the response, even where global increases are not observed with present methodology. Deactivation of the inward K+ channel is abolished in the presence of internal Ca2+ chelator, but not by external Ca2+ chelator, arguing for release from internal stores. ABA-induced turnover in the polyphosphoinositide cycle occurs within 30 s, and may precede the electrical changes. Activation of the outward K+ channel is Ca(2+)-independent; changes in cytoplasmic pH, of unknown origin, may be responsible.
MacRobbie
E A
EA
Department of Plant Sciences, University of Cambridge, UK.
D000040:Abscisic Acid / Q000502:physiology; D002118:Calcium / Q000502:physiology*; D002614:Chelating Agents / Q000494:pharmacology; D007295:Inositol Phosphates / Q000502:physiology; D015640:Ion Channel Gating / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D008954:Models, Biological; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000502:physiology; D059828:Plant Cells; D018521:Plant Physiological Phenomena; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D015398:Signal Transduction
D002614:Chelating Agents; D007295:Inositol Phosphates; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D015221:Potassium Channels; D000040:Abscisic Acid; D002118:Calcium