Response of plasma membrane H⁺-ATPase of rice roots to the P deficiency

Rice plants (Oryza sativa L. Japonica ssp. cv. Wuyujing) were fed with and without phosphate in hydroponics culture experiment. At the seedling stage the plasma membrane vesicles of roots were isolated by two-phase system. The plasma membrane H+-ATPase hydrolytic activity was analyzed for elucidating the response of the plasma membrane H+-ATPase of rice root to P deficiency. The results showed that: (1) plasma membrane H+-ATPase hydrolytic activity and ATPase Km, Vmax obtained from P deficient rice root were lower than those from P sufficient rice root; (2) the optimum pH of the plasma membrane H+-ATPase of P deficient rice root was 6.2, but was 6.4 for that of P-sufficient root. (3) But the western blot showed that the enzyme concentration of plasma membrane H+-ATPase from P deficient rice root was similar to that from P sufficient rice root. The results indicated that the lower activity of H+-ATPase from P deficient rice root was not due to the decreased number of H+-ATPase units per membrane area. The different H+-ATPase isoforms might be induced in the P deficient rice root in comparison with the P sufficient rice root. It could be an adaptation mechanism of plasma membrane H+-ATPase of rice root to P deficiency.