The effect of glyceollin on proton leakage in Phytophthora megasperma f. sp. glycinea plasma membrane and red beet tonoplast vesicles

Proton transport in sealed plasma membrane vesicles from Phytophthora megasperma f. sp. glycinea was inhibited by glyceollin. At 50 μM glyceollin no proton transport could be observed. Glyceollin at this concentration did not significantly affect the H⁺-ATPase responsible for proton pumping at the plasma membrane. Passive proton conductance increased significantly in the presence of glyceollin. These results suggest that glyceollin may inhibit fungal growth by diminishing the proton gradient necessary for solute uptake. Inhibition of the proton gradient appears to be due to increased proton conductance across the membrane in the presence of glyceollin and not inhibition of the H⁺-ATPase. Glyceollin also caused increased passive proton conductance in red beet (Beta vulgaris L.) tonoplast vesicles at levels where the ATPase was minimally inhibited. These data taken together suggest that a primary phytotoxic effect of glyceollin may be to cause proton or ion leakage across membranes.