INFLUENCE OF ATPASE ACTIVITY ON PPI DEPENDENT H-TRANSPORT IN TONOPLAST VESICLES OF ACER-PSEUDOPLATANUS()

Tonoplast H+-ATPase and H+-pyrophosphatase (H+-PPase) were previously characterized in Acer pseudoplatanus cells (A. Pugin et al., Plant Sci ., 73 (1991) 23-34; A. Fraichard et al., Plant Physiol. Biochem., 31 ( 1993) 349-359). The present study concerns the relationships between t hese two enzymes in vitro. ATP and PPi hydrolysis were additive and th e inhibition of one did not affect the activity of the second one. ATP and PPi H+-transports were also additive. The H+-PPase inhibition did not change ATP-dependent,H+-transport but H+-ATPase inhibition inhibi ted the PPi dependent H+-transport. Because H+-PPase was reported to t ransport H+ and K+ into the vacuole (Davies et al., Proc. Natl. Acad. Sci. USA, 89 (1992) 11701-11705), these results led us to suggest that the inhibition of the H+-ATPase activity could modify the H+/K+ stoic hiometry for the benefit of K+-transport.