Research advances on nitrate nitrogen reutilization by proton pump of tonoplast and its relation to nitrogen use efficiency.

Large amount of N03 --N are accumulated in vacuole, and cannot be timeously reducted, reutilized and transported into cytoplasm. It is the main reason for great N03 --N accumulation in vacuole and nitrogen (N) use efficiency cannot be further improved. Transport mechanism of N03 --N across tonoplast is explained in this paper, there are two proton pumps (H+-ATPase and H+-PPase) on tonoplast with absolutely different biology functions and physical characteristic. Mg.ATP and Mg.PPi are the specific substrates of H+-ATPase and H+-PPase respectively, hydrolysis H+ is pumped into vacuole, and contribution to build electrochemical proton gradient between cytoplasm and vacuole. N03 --N transport from vacuole to cytoplasm greatly depends on electrochemical proton gradient, N03 --N transport from cytoplasm to vacuole is mainly achieved by vacuole H+/N03 - antiport system, while symport system (vacuole N03 --N combined with anion) is of benefit for vacuole N03 --N transporting into cytoplasm. N03 --N transported by proton pump of tonoplast is influenced by NR activity in cytoplasm, N03 --N can be continuing assimilation and reduction by NR in cytoplasm, and accelerating vacuole N03 --N transported into cytoplasm. These results will supply references and research forecast for further study on efficiency and practicable methods of N utilization, and improving reuse efficiency of N03 --N in plant tissues.