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

Large amount of N0 3 - -N are accumulated in vacuole, and cannot be timeously reducted, reutilized and transported into cytoplasm. It is the main reason for great N0 3 - -N accumulation in vacuole and nitrogen (N) use efficiency cannot be further improved. Transport mechanism of N0 3 - -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. N0 3 - -N transport from vacuole to cytoplasm greatly depends on electrochemical proton gradient, N0 3 - -N transport from cytoplasm to vacuole is mainly achieved by vacuole H + /N0 3 - antiport system, while symport system (vacuole N0 3 - -N combined with anion) is of benefit for vacuole N0 3 - -N transporting into cytoplasm. N0 3 - -N transported by proton pump of tonoplast is influenced by NR activity in cytoplasm, N0 3 - -N can be continuing assimilation and reduction by NR in cytoplasm, and accelerating vacuole N0 3 - -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 N0 3 - -N in plant tissues.