Evidence for an action of fusicoccin on the vacuolar pH of acer pseudoplatanus cells in suspension culture

Abstract The pH, malic acid and K + contents of the cell sap extracted from frozen thawed Acer pseudoplatanus cells were measured. A fusicoccin (FC) treatment of the cells induced an increase pf the pH and malic acid and K + contents indicating that a vacuolar pH modification was probably involved in FC action. Even though the decrease of the pH of the culture medium was measureable after a short period of FC treatment (10–15 min), at least 1 h was necessary for an increase of sap pH to be significant. The assumption of a vacuolar pH modification is supported by the modification of the distribution of [ 14 C] nicotine molecules between the cells and their culture medium induced by the FC treatment. As this lipophilic base is absorbed by diffusion of the neutral form and concentrated as ions in the acidic compartments of the cells (i.e. mainly the vacuole) FC action on nicotine accumulation can be interpreted as evidence for a vacuolar pH modification. Possible mechanisms of this FC action are tentatively discussed.