Vacuolar pH regulation in Chara australis.

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Abstract
The vacuolar pH (pHv) was modified by vacuolar perfusion of internodal cells of C. australis. After perfusion, the cell was incubated in artificial pond water. The cell sap was isolated after various incubation periods and its pH was measured with a glass pH microelectrode. The time course of pHv change also was measured in situ with an intracellular pH-sensitive antimony electrode. When the natural cell sap (pH 5) was replaced with artifical cell sap of pH 6.0, the pH gradually returned to 5. This recovery process was inhibited by DCCD [dicyclohexylcarbodiimide], and inhibitor of H+-ATPase. When the natural cell sap was replaced with an artifical cell sap of pH 4.2, the pH quickly shifted to the alkaline direction (reaching a pH of 6, after which it returned to the original value, pH 5) or it returned directly to the original value. This process was not inhibited by DCCD. Apparently the pHv is regulated by the balance between the active influx of H+ into the vacuole provided by the H+-pump of the tonoplast and the passive efflux of H+ from the vacuole.