Calcium channels in higher plants

Calcium channels are involved principally in signal transduction. Their opening results in increased cytoplasmic Ca2+ concentration, and the spatial and temporal variations in this are thought to elicit specific physiological responses to diverse biotic and abiotic stimuli. Calcium-permeable channels have been recorded in the plasma membrane, tonoplast, endoplasmic reticulum, chloroplast and nuclear membranes of plant cells. This article reviews their electrophysiological properties and discusses their physiological roles. Emphasis is placed on the voltage-dependent and elicitor-activated Ca2+ channels of the plasma membrane and the depolarisation-activated (SV), hyperpolarisation-activated, IP3- and cADPR-dependent Ca2+ channels of the tonoplast. The closing of stomatal guard cells in the presence of abscisic acid (ABA)is used to illustrate the co-ordination of Ca2+ channel activities during a physiological response.