| Abstract: | Beffagna, N. and Romani, G. 1988. Effects of two plasmalemmaATPase inhibitors on H+ extrusion and intracellular pH in Elodeadensa leaves.—J. exp. Bot. 39: 1033–1043. Elodea leaves in the dark show very little exchange of H+ withthe medium in the external pH range between 5.0 and 6.0. Thepresence of fusicoccin and potassium in the medium markedlystimulates H+ extrusion. Fusicoccin- and K+ -induced H+ extrusionis inhibited by either erythrosin B (EB) or Na-orthovanadate,two inhibitors of H+ transporting plasma membrane ATPase. EBcompletely inhibits it from the first 30 min of treatment, whensupplied at pH 5.5 at a concentration of 30 mmol m–3.Vanadate also inhibits H+ extrusion, this effect becoming evidentonly after 45 min of treatment. After this time inhibition iscomplete with 250 mmol m–3 vanadate but only partial forlower concentrations. In the presence of either inhibitor the intracellular pH, measuredas cell sap pH, is significantly lowered. When the intracellularpH changes are determined on vacuole and, separately, on cytoplasmby the weak acid and base distribution method, acidificationof both compartments is found to accompany the blocking of H+extrusion by either of the inhibitors. Key words: Intracellular pH, vanadate, erythrosin B, H+pumping |
