Adaptation of plasma membrane H+ ATPase and H+ pump to P deficiency in rice roots

The plasma membrane (PM) H+ ATPase is involved in the plant response to nutrient deficiency. However, adaptation of this enzyme in monocotyledon plants to phosphorus (P) deficiency lacks direct evidence. In this study, we detected that P deficient roots of rice (Oryza Sativa L.) could acidify the rhizosphere. We further isolated the PM from rice roots and analyzed the activity of PM H+ ATPase. In vitro, P deficient rice roots showed about 30% higher activity of PM H+ ATPase than the P sufficient roots at assay of pH 6.0. The P deficiency resulted in a decrease of the substrate affinity value (Km) of PM H+ ATPase. The proton pumping activity of membrane vesicles from the P deficient roots was about 70% higher than that from P sufficient roots. Western blotting analysis indicated that higher activity of PM H+ ATPase in P deficient roots was related to a slightly increase of PM H+ ATPase protein abundance in comparison with that in P sufficient roots. Taken together, our results demonstrate that the P deficiency enhanced activities of both PM H+-ATPase and H+ pump, which contributed to the rhizosphere acidification in rice roots.