The Mechanism of Chloride Transport in Characean Cells

S ummary Active chloride uptake by cells of Chara corallina decreases as the pH of the bathing solution is increased, using a range of buffers. Superimposed on this effect, large stimulations of Cl − uptake can be obtained by the addition of imidazole and tris buffers or ammonium sulphate. ‘Stimulated’ or ‘normal’ Cl − influxes respond similarly to the presence of metabolic inhibitors. It is suggested that these effects are not due to changes in photosynthesis or respiration, but reflect the dependence of Cl − transport on the pH gradient across the plasmalemma. Possible ways in which Cl − transport might be linked to H + or OH − fluxes are discussed. It is proposed that the pH gradient across the plasmalemma is controlled by charge‐separating reactions which produce an active H + efflux, and that Cl − uptake is linked to OH − efflux by ion‐exchange reactions. The metabolic implications of this scheme are discussed in detail, with reference to previous work on Characean and other plant cells.