The Mechanism Of Plasma Membrane H~+-ATPase Involved In The Uptake Of Nitrogen/Phosphorus By Rice Roots

The plasma membrane H+pump is also called plasma membrane H+-ATPase(PM H+-ATPase), It’s major role is to pump H+out of the plant cell by hydrolysis of ATP, and forms H+electrochemical gradient across the plasma membrane to promote the ions across the membrane. In this study, we investigate the physiological and molecular mechanisms of PM H+-ATPase in the uptake of nitrogen and phosphorus nutrients by rice roots.Ammonium is the major N resource. However, absorbing a large number of ammonium will cause roots to secrete large amounts of H+, and led to the acidification of the rhizosphere. Therefore, the terrestrial plants growth will be inhibited by ammonium nutrition, which named as ammonium toxicity.Because of rice living in the flooded soil with low activity of nitrification, compared to nitrate nutrition, ammonium is the major N resource. Rice is a typical ammonium-tolerant plant. Our previous studies showed that the PM H+-ATPase plays an important role in this process.In this study, we use the transgenic rice of OsA8overexpression line (OE#1) as our material and study the basic physiological characteristics to investigate the ammonium-resistance mechanism in relation to the PM H+-ATPase activity. we also found that, compared to nitrate nutrition, ammonium stimulated root to absorb more phosphorus. The underlying mechanisms of PM H+-ATPase in this process was also studied.The results showed that:1The rice cultivated in different concentration of ammonium showed the following characteristics:when NH+≤1mM, the rice showed nitrogen deficiency, at1mM NH4+, the rice growth best. However, over2mM NH4+, the rice root growth was inhibited. We found the activity of PM H+-ATPase was increased when the ammonium concentraction increased and reach the highest level at the1mM NH4+But the activity decreased at the2mM NH4+concentration. The result of western-blot showed that the PM H+-ATPase protein concentration is in consistent with its activity. At the transcriptional expression level, there are three genes OSA2,OSA3and OSA7was detected in root and four genes OSA2,OSA3,OSA7and OSA9were detected in shoot. Therefore, the PM H+-ATPase is involved in the mechanism of rice tolerance to ammonium.2We found that the germination rate and primary root growth rate of OE#1were higher than WT. The activity of PM H+-ATPase in OE#1root was highter than WT. the results confirmed that the cell elongation is related to the PM H+-ATPase, which acidificed the apoplast(acid growth theory).3In order to explore the mechanism of PM H+-ATPase involved in the promotion of phosphorus absorption by ammonium. Rice plants were treated by different form of nitrigon nutrition. Results showed that the phosphorus content in ammonium treated rice plants was higher than that treated by nitrate. The activity of PM H+-ATPase of rice roots under ammonium nutrition was higher than that under nitrate. Western-blot analysis showed that the different enzyme concentration caused the different activity of PM H+-ATPase. The results also showed that ammonium induced more PM H+-ATPase isogenes and phosphate transporter genes at transcriptional level.33P absorption experimental showed that the PM H+-ATPase was directly involved in ammonium stimulated phosphorus absorption process.