Nitrate nitrogen reutilization based on proton pump of vacuole membrane: A review

The fact that large amount of NO3- -N accumulated in vacuole cannot be timely transported into cytoplasm and then reduced and reutilized is the main reason for the great NO3- -N accumulation in vacuole and for the nitrogen use efficiency unable to be further improved. This paper reviewed the transportation mechanisms of NO3- -N in vacuole membrane. Vacuole membrane has two proton pumps, H+-ATPase and H+-PPase, which have absolutely different biological functions and physical characteristics, with Mg·ATP and Mg·PPi as the specific substrates, respectively. The H+ obtained through the hydrolysis of these substrates is pumped into vacuole, and contributes to the electrochemical proton gradient between cytoplasm and vacuole. The NO3- -N transportation from vacuole to cytoplasm is greatly depended on the electrochemical proton gradient. The NO3- -N transportation from cytoplasm to vacuole is mainly depended on the vacuole H+/NO3- antiport system, while the symport consisted of vacuole NO3- -N and other anions benefits the transportation of NO3- -N from vacuole to cytoplasm. The transportation of NO3- -N based on the proton pump of vacuole membrane is also affected by the cytoplasm nitrate reductase (NR) activity. Cytoplasm NR can continuously assimilate and reduce NO3- -N, making the NO3- -N accumulated in vacuole more transported into cytoplasm and utilized. This review could provide reference for the further study on the efficient and practicable measures of plant nitrogen utilization, and for improving the NO3- -N reutilization efficiency.