Characterization of Two Proton Transport systems in the Tonoplast of Plasmalemma-Permeabilized Nitella Cells

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ATP-dependent and PP_i-dependent H^+_transport systems of the tonoplast were characterized in plasmalemma-permeabilized Nitella cells, where direct access to the protoplasmic surface of the tonoplast was possible. Since H^+ transport across the tonoplast can be measured in situ, the identity of the membrane responsible for H^+ pumping is unequivocal. H^+ transport was evaluated by the accumulation of neutral red. While both transport systems were obligately dependent on Mg^<2+>, the two transport systems showed completely different sensitivity to NO^-_3 and K^+, suggesting the presence of two types of H^+-pumps in Nitella tonoplast. NO^-_3 applied to the protoplasmic surface, completely and reversibly inhibited ATP-dependent transport but had no effect on PP_i-dependent transport. By contrast, NO^-_3 applied into the vacuole by the vacuolar perfusion technique did not inhibit ATP-dependent or PP_i-dependent H^+ transport. Replacement of K^+ with the organic cation, BTP, inhibited PP_i-dependent transport but not the ATP-dependent one, indicating that PP_i-dependent transport is K^+ dependent. The sensitivities of the H^+ transport systems found in the tonoplast of Nitella are quite similar to those of higher plant tonoplasts.
日本植物生理学会の論文