The effect of inhibitors of plasma membrane redox reactions on proton excretion by plant cells

Plant cells excrete protons via an electrogenic proton pump, the K + ‐stimulated, Mg 2+ ‐dependent H + ‐ATPasc, located on the cytoplasmic side of the plasma membrane. Plasma membrane redox reactions are also coupled to proton excretion. Various inhibitors were used on carrot ( Daucus carola L.) cells in an attempt to distinguish between the two processes. Inhibitors of electron transport reactions in the plasma membrane (chloroquine, 8‐hydroxyquinolinc, 4,7‐dichloroquinolinc and retinoic acid) inhibited ferricyanide‐induced proton excretion by 37–100%, while they inhibited potassium ferricyanide reduction, a measure of plasma membrane redox activity, by 42–100%. The above‐mentioned quinolines and retinoic acid inhibited cell growth by 49–98%, with the exception of chloroquine, which stimulated carrot cell growth by 36%.