Stimulation of phosphorus uptake by ammonium nutrition involves plasma membrane H+ ATPase in rice roots
Nitrogen, especially NH 4 + , can stimulate the uptake of phosphorus in plants, but the underlying mechanisms have not been clearly elucidated. Because phosphate is taken up via an anion/H+ co-transport process, we propose that the stimulated uptake of phosphorus by NH 4 + versus NO 3 - nutrition may be related to the activity of plasma membrane H+ ATPase. In the present study, we investigated the effect of NH 4 + and NO 3 - on phosphorus uptake and plasma membrane H+ ATPase activity in rice.
Rice plants were cultivated in a hydroponic solution with NH 4 + or NO 3 - . After 15 days of cultivation, phosphorus content was determined. Root plasma membrane was isolated using a two-phase partitioning system and hydrolytic H+-ATPase activity was determined by measuring the Pi concentration after a 30-min hydrolysis reaction. Relative expression of plasma membrane H+ ATPase genes was analyzed by real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR). H+ ATPase enzyme concentration in the plasma membrane was detected by western blot. For 33P uptake experiments, rice roots were incubated in the nutrient solution with addition of H 3 33 PO4.
P content in both the roots and shoots of rice plants supplemented with NH 4 + was significantly higher than P content in plants grown with NO 3 - . Plasma membrane H+ ATPase activity in NH 4 + -fed rice roots was significantly higher than that in NO 3 - -fed rice roots. Real-time qRT-PCR and western blot results indicated that the higher activity of plasma membrane H+ ATPase in NH 4 + -fed rice roots could be attributed to increased expression of the OSA1, OSA3, OSA7, OSA8 and OSA9 genes and an increase in H+ ATPase enzyme concentration in the plasma membrane. Results from 33P uptake experiments showed that rice roots incubated with NH 4 + absorbed more 33P during the four-hour incubation than did rice roots incubated with NO 3 - . Vanadate inhibited 33P uptake in rice roots supplied with NH 4 + , while fusicoccin stimulated 33P uptake under NO 3 - nutrition.
Taken together, these results suggest an involvement of plasma membrane H+ ATPase in the stimulated uptake of phosphorus by rice roots supplemented with NH 4 + .
KeywordsAmmonium Nitrate Phosphorus uptake Plasma membrane H+ ATPase Rice (Oryza sativa L.)
This work was supported by Natural Science Foundation of China (NSFC 30971864).
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