Regulation of the Cytoplasmic pH ofChara corallina: Response to Changes in External pH

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Abstract
Effects of external pH (pHo) on the cytoplasmic pH (pHc) of Chara corallina have been measured with the weak acid 5, 5-dimethyloxazolidine-2, 4-dione (DMO) following standardized pretreatment of cells in solutions at pHo 4.5, 6.3 and 8.3. Irrespective of pHc during pretreatment, pHo responded to pHo during the experimental periods of 150–180 min or (in one experiment) 90–110 min. There were increases or decreases of about 0.5 in pHo when cells were transferred from pHo 4.5 to 8.3 or vice versa. In the dark pHc was 0.2–0.3 units lower than the corresponding value in the light. The results are discussed in relation to the factors involved in the regulation of pHc in C. corallina, which may begin to break down below about pHo4.5, as indicated by relatively large decreases in pHc at low pHo.