Electric characteristics of the vacuolar membrane of Chara in relation to pH regulation.

Abstract

ABSTRACT. The vacuolar pH of Chara internodal cells was modified by vacuolar perfusion, and changes in membrane potential and membrane resistance of the tonoplast in response to the vacuolar pH (pHv) change were studied by anesthetizing the cell with 110 mM KCl in the external medium. Under this condition the responses of the vacuolar potential (Ev o) and resistance (Rvo) are assumed to reflect the responses of the tonoplast. E, o showed scarcely any sensitivity to the pHv when the KCl concentration of the vacuole ([KCl]v) was high (100 mM), but it changed by 30 mV in response to changes in the pHv from 5.5 to 7.5 when the [KCl]v was as low as 0.1 mM. This pHv sensitivity of Ev o was suppressed by DCCD, an inhibitor of H+-ATPase.Tonoplast vesicles were prepared from an internodal cell, and the effect of MgATP on their internal pHs was studied by estimating the accumulation of neutral red. A high accumulation of the pigment was found when MgATP was present in the external medium, but the color faded away when ATP was absent. These results together with the effect of DCCD on the Evo. indicate that there is an ATP-dependent electrogenic H+-pump in the tonoplasts of Chara internodal cells and that this electrogenicity is very small under normal conditions in which the natural cell sap contains about 100 mM KCl.Membrane characteristics of the tonoplast were compared with those of the plasmalemma with respect to their passive permeabilities to K+ and H+ and to the pump conductance.

Short‐term pH regulation in plants

“…They added 50 mM propionic acid (pH^, 6.5) and found pH^ to be rapidly decreased by about 0.3 pH units; but, in contrast to cytoplasmic pH, there was no significant recovery. However, these findings are by no means contradictory to the observations of Moriyasu et al (1984a), because acidifying cellular compartments with externally added weak acids is an altogether different experiment than perfusion and subsequent exchange of the cell sap. Weak acids have the tendency to clamp internal pH, unless active mechanisms prevent it.…”

“…Using antimony electrodes, Moriyasu et al (1984a) demonstrated pH^, regulation in perfused internodal cells of Chara australis. After replacing the natural ceil sap (pH 5) by artificial sap of pH 6, the pH^, gradually returned to 5, a process inhibited by DCCD.…”

Magnetic detection of a single action potential in Chara corallina internodal cells

“…The Plexiglas tube was 175 mm long. Recording of the action potential was similar to that described previously (Moriyasu et al, 1984;Clint and MacRobbie, 1987). Briefly, the Plexiglas support compartment was filled with 100 mM KCl.…”

Cell physiological aspects of the plasma membrane electrogenic H + pump

“…The technique of vacuolar perfusion has contributed further to studies on the mechanism of excitation of the tonoplast , measurement of the motive force of cytoplasmic streaming (Tazawa 1968), amino acid metabolism (Sakano and Tazawa 1985), pH regulation of the vacuole (Moriyasu et al 1984a(Moriyasu et al , 1984b and the proteases in the vacuolar sap (Moriyasu and Tazawa 1986;Moriyasu et al 1987).…”