Regulation of the structure and catalytic properties of plasma membrane H+-ATPase involved in adaptation of two reed ecotypes to their different habitats

The properties and kinetics of ATP and p-nitrophenyl phosphate (PNPP) hydrolysis activities of plasma membrane H+-ATPase from the two reed ecot ypes, swamp reed (SR) and dune reed (DR), were investigated. The pH optimum of the plasma membrane H+-ATPase in both reed ecotypes was similar but the sensitivity of the enzyme to the reaction medium pH seemed to be higher in DR than that in SR. Compared to SR, the DR exhibited a higher V-max value for ATP hydrolysis whereas the K-m value was almost similar in both reed ecotypes. The PNPP hydrolysis of the plasma membrane H+-ATPase was also studied in both reed ecotypes at increasing PNPP concentrations. K-m and V-max for PNPP hydrolysis showed great differences in the two reed ecotypes and in DR the K-m and V-max values were 2- and 10-fold, respectively, higher than those in SR. The ATP hydrolysis activity of the plasma membrane was markedly inhibited by hydroxylamine in both reed ecotypes, and the percentage inhibition of ATP hydrolysis rate seemed higher in DR than that in SR. In addition, the structure or property of the C-terminal end of the plasma membrane H+-ATPase were also different in the two reed ecotypes. These data suggest that different isoforms of the plasma membrane H+-ATPase might be developed and involved in the adaptation of the plant to the long-term drought-prone habitat.