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

Effects of external pH (pH_o) on the cytoplasmic pH (pH_c) ofChara corallina have been measured with the weak acid 5, 5-dimethyloxazolidine-2,4-dione (DMO) following standardized pretreatment of cells insolutions at pHo 4.5, 6.3 and 8.3. Irrespective of pH_c duringpretreatment, pH_o responded to pHo during the experimental periodsof 150–180 min or (in one experiment) 90–110 min.There were increases or decreases of about 0.5 in pHo when cellswere transferred from pH_o 4.5 to 8.3 or vice versa. In the darkpH_c was 0.2–0.3 units lower than the corresponding valuein the light. The results are discussed in relation to the factorsinvolved in the regulation of pH_c in C. corallina, which maybegin to break down below about pH_o4.5, as indicated by relativelylarge decreases in pH_c at low pH_o. Key words: Chara corallina, Cytoplasmic pH, External pH, DMO