Control of Intracellular pH inChara corallinaduring Uptake of Weak Acid

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Abstract
Butyric acid was used to acidify the cytoplasm of cells of Chara corallina in order to study the mechanisms that regulate intracellular pH. Butyric acid was found to enter the cell rapidly, predominantly as the undissociated acid, and to dissociate in the cytoplasm to yield high concentrations of the butyrate anion. A rapid reduction in cytoplasmic pH was followed by partial recovery. The reductions in cytoplasmic pH resulting from butyrate accumulation were small compared to the proton load calculated from the cytoplasmic buffering capacity and intracellular dissociation of butyric acid. The cytoplasmic and vacuolar buffering capacities, calculated from titration of cell extracts, were 17.9 and 0.5 mol m−3 per pH unit respectively. It was concluded that pH control in Chara during weak acid accumulation was mainly due to membrane transport (active efflux) of protons. The factors which might determine the rate and extent of proton efflux, such as the energy supply and the availability of ions for charge balance, were examined. Butyrate strongly inhibited photosynthesis and caused a slight reduction in the rate of respiration. The mechanism of inhibition of photosynthesis is discussed in relation to the reported effects of weak acids on isolated chloroplasts.