Artificial Control of Cytoplasmic pH and Its Bearin~ on Cytoplasmic Streaming, Electrogenesis and Excitability of Characeae Cells

Effects of changing the cytoplasmic pH on the cytoplasmic streaming, membrane potential and membrane excitability were studied in tonoplast-free cells of Chara australia and NiteUo~osis obtusa. The cytoplasmic pit was varied by internal perfusion of pH-buffered media. Nitellopsis cells were perfused only once, while Chara cells were perfused twice to control the pH more accurately. In both materials the rate of cytoplasmic streaming was maximum at about pH 7, low at pH 8,5-9 and almest zero at pH 5-5.5. The membrane potential was most negative at about pH 7. In Chara the membrane potential supported by Mg.ATP was strongly inhibite4 at pH 5.5 and almost zero at pH 9, supporting the resul~s obtained by Fujii et al. (1979) on cells of Chara australis which were perfused once. The action potential could be induced by electrical stimulation in Chara at pH 6.0-9.0 and in Nitellopsis at pH 6.6 7.9. The membrane resistance of Nitellopsis was high at acidic and neutral pit values and low at alkaline pit, while that of Chara was low at both acidic and alkaline pit values.