PYROPHOSPHATE AND H-PYROPHOSPHATASE MAINTAIN THE VACUOLAR PROTON GRADIENT IN METABOLIC INHIBITOR-TREATED ACER-PSEUDOPLATANUS CELLS()

The effect of metabolic inhibitors (KCN and 2-deoxy-D-glucose) on the vacuolar proton gradient, monitored by acridine orange, was assayed in Acer pseudoplatanus cells. Potassium cyanide plus 2-deoxy-D-glucose s lightly lowered this gradient, while cellular ATP level was strongly d ecreased and inorganic pyrophosphate (PPi) content was halved. Two pho sphatase inhibitors (imidodiphosphate and KF) restored the PPi level i n KCN-treated cells, but decreased the vacuolar proton gradient by inh ibiting H+-PP(i)ase. These results, hence, suggest that tonoplast H+-P P(i)ase is especially responsible for the maintenance of vacuolar Delt a pH and that this enzyme is the major scavenger of cytoplasmic PPi in cells treated with metabolic inhibitors.