Ca2+-dependent Cl− efflux in tonoplast-free cells ofNitellopsis obtusa

Abstract

Summary. In order to demonstrate the presence of a Ca'--activated Cl--channel in the Nitellopsis plasmalemma, tonoplastfree cells were prepared and their intracellular Ca -'+ concentration was modified by internal perfusion. An increase in the Ca -'+ concentration caused a large CI efflux with a concomitant depolarization of the membrane potential. These changes were for the most part reversible. The critical Ca 2+ concentration was about 4.0/*M. Neither the CI-efflux nor the membrane depolarization showed a time-dependent inactivation. A C1 -channel blocker, A-9-C (9-anthracenecarboxylic acid) reduced both the C1 efflux and the magnitude of the membrane potential depolarization. A small increase in the intracellular Ca > concentration, which is caused by membrane excitation of tonoplast-free cells is not sufficient to activate this Ca2+-dependent Cl--channel.

Ion channel gating in plants: Physiological implications and integration for stomatal function

“…Findlay & Hope 1964;Lunevsky et al, 1983;Kataev, Zherelova & Berestovsky, 1984;Caldwell, Van Brunt & Harold, 1986;Shiina & Tazawa, 1988;Thiel, MacRobbie & Hanke, 1990; see also Tester, 1990); only very recently has attention turned to the presence of Cl-channels in traditionally nonexcitable higher-plant cells (Falke et al, 1987(Falke et al, , 1988Schauf & Wilson, 1987;Fairley & Walker, 1989; see also Okazaki & Tazawa, 1990). It is all the more striking, therefore, that a dominant theme among the recent discoveries is the role of Ca 2 + in activating or modulating channel current (Boult et al, 1989;Schroeder & Hagiwara, 1989;.…”

“…Calcium channels and fluxes activated by inositol 1,4,5-trisphosphate (IP3) are known in tonoplast-enriched vesicles from Arena (Schumaker & Sze, 1987), and the tonoplast of Beta Alexandre, Lassalles & Kado, 1990;Brosnan & Sanders, 1990) and Acer (Ranjeva, Carrasco & Boudet, 1988;Canut et al, 1989); Ca 2 + release from intracellular stores in guard cells is inferred from recent observations that the cytoplasmic Ca 2+ signal--and consequent changes in K + channel and other (anion? see also Lunevsky et al, 1983;Shiina & Tazawa, 1988;Thiel et al, 1990) currents (above)--can be induced also following the release of caged IP 3 and in the presence of La 3+ outside (Blatt et al, 1990a;Gilroy et al, 1990). Schroeder and Hagiwara (1990) have attempted to identify the Ca 2 + conductance at the plasma membrane, using simultaneous voltage-clamp measurements and Ca2+-dependent dye fluorescence to distinguish this from Ca 2+ release across the tonoplast of Vicia guard cell protoplasts.…”

Rapid effect of light on the K+ channel in the plasmalemma ofNitella

“…The phenomena observed in our investigations are not related to the action potential. However, Shiina and Tazawa (1988) came to the conclusion that the C1-channel in tonoplastfree cells of Nitellopsis obtusa is not opened by membrane depolarization, but by the increase of cytosolic Ca 2+ concentration, as shown by Kikuyama (1986) who could initiate a C1-spike by microinjection of Ca 2+. Thus, the chloride channels could also be opened by a decrease of pCa originating from other processes.…”

“…The only problem is that the magnitude of the increase in [Ca2+]cyt (caused by the downward steps in light intensity) has to be quite high for opening the Ct-channel. Shiina and Tazawa (1988) found a value of 4 mmol 9 m -3 for half-maximum opening. It is difficult to estimate the changes in pCa in our measurements, because the local changes in the narrow space between chloroplasts and plasmalemma may be much greater than those measured by Miller and Sanders (1987) in the bulk cytoplasm.…”

Roles of Ion Channels in Initiation of Signal Transduction in Higher Plants.

“…In addition, further work is necessary to determine if, as in guard cells (Figure l), nonselective anion channels may be involved in the earty signal transduction leading to anion channel activation in response to other stimuli. It is important to keep in mind that in Characean algae, anion channel activation depends on Ca2+ influx at the plasma membrane (Williamson and Ashley, 1982; Lunevsky et al, 1983; Shiina and Tazawa, 1988). Similar regulation of anion channels may also occur ín higher plant cells.…”