Induction of vacuolar ATPase and mitochondrial ATP synthase by aluminum inan aluminum-resistant cultivar of wheat

Two 51-kD aluminum (A1)-induced proteins (RMP51, root membrane proteins of 51 kD) were recently discovered in an aluminum-resistant cultivar of wheat (Triticum aestivum) cv PT741 (Basu et al., 1994a). These proteins segregate with the aluminum resistance phenotype in a segregating population arising from a cross between A1-resistant cv PT741 and A1-sensitive cv Katepwa (Ta ylor et al., 1997). The proteins have been purified by continuous elution e lectrophoresis and analyzed by peptide microsequencing. Sequence analysis o f the purified peptides revealed that they are homologous to the B subunit of the vacuolar H+ -ATPase (V-ATPase) and the alpha- and beta -subunits of the mitochondrial ATP synthase (F1F0-ATPase). To confirm that these ATPases are induced by A1, ATPase activity and transcript levels were analyzed und er A1 stress. Both V-ATPase and F1F0-ATPase activities were induced by A1 a nd responded in a dose-dependent manner to 0 to 150 muM Al. In contrast, pl asma membrane H+-ATPase (P-ATPase) activity decreased to 0.5x control level s, even when plants were exposed to 25 muM Al. Northern analysis showed tha t the transcript encoding the B subunit of V-ATPase increased by 2.2x in a dose-dependent manner, whereas levels of the transcript encoding the alpha -subunit of F1F0-ATPase remained constant. The effect of A1 on ATPase activ ity in other cultivars was also examined. The A1-resistant cultivar, cv PT7 41, was the only cultivar to show induction of V- and F1F0-ATPases. These r esults suggest that the V-ATPase in cv PT741 is responding specifically to A1 stress with the ATP required for its activity supplied by ATP synthase t o maintain energy balance within the cell.