Ca2+ Increases the Cl ~ Efflux of the Permeabilized Chara

An internode of Chara was permeabilized as described by Shimmen and Tazawa [(1983) Pro-toplasma 117: 93]. The Cl " efflux of the permeabilized cell increased when the extracellular Ca2+ concentration was increased, and the degree of the increase was dependent on the Ca2+ concentra-tion. This suggests that the Cl ~ channel in the tonoplast was activated by Ca2+. Key words: Ca2+ — Chara — Cl ~ channel — Permeabilized cell — Tonoplast. Excitation of characean cells has been a subject of in-tensive studies in plant electrophysiology (Umrath 1930, Sibaoka 1958, Hope and Walker 1975). One of the most important characteristics of the cell may be the existence of two membranes, the plasmalemma and the tonoplast. Findlay and Hope (1964) and Findlay (1970) showed that not only the plasmalemma but also the tonoplast generates action potential upon electrical stimulation. Kikuyama and Tazawa (1976) clearly demonstrated that the tonoplast became highly permeable to Cl ~ during the action poten