EFFECTS OF BAFILOMYCIN A(1) AND METABOLIC-INHIBITORS ON THE MAINTENANCE OF VACUOLAR ACIDITY IN MAIZE ROOT HAIR-CELLS

Proton pumps of tonoplast membranes have been studied extensively in v itro, but data concerning their regulation in vivo are lacking. Effect s of either anoxia, or the addition of KCN, 2-deoxy-d-glucose (deoxy-g lucose), or bafilomycin-A(1) (BAF) on vacuolar pH of maize (Zea mays L .) root hair cells were followed by fluorescence microscopy after load ing of 2'7'-bis-(2-carboxyethyl)-5-(and-6) carboxyfluorescein. Root ha ir cells were able to maintain vacuolar acidity for at least 2 h in th e presence of either 10 mM KCN or 50 mM deoxy-glucose or during anoxia . Treatments with either deoxyglucose or KCN reduced total tissue ATP move than anoxia. ADP accumulated during anoxia and treatment with KCN as detected by in vivo P-31-NMR spectroscopy, but not during deoxy-gl ucose treatment. With control roots and roots treated with deoxy-gluco se, the presence of BAF, a specific inhibitor of the V-type ATPase, ca used alkalization of the vacuolar pH. However, either in the presence of KCN or under anoxic conditions, BAF was relatively ineffective in d issipating vacuolar acidity. Therefore, under anoxia or in the presenc e of KCN, unlike the situation with air or deoxy-glucose, the V-type A TPase apparently is not required for maintenance of vacuolar acidity.