Compared with sole nitrate (NO_(3)^(-)) or sole ammonium (NH_(4)^(+)) supply,mixed nitrogen (N) supply may promote growth of maize seedlings.Previous study suggested that mixed N supply not only increased photosynthes...Compared with sole nitrate (NO_(3)^(-)) or sole ammonium (NH_(4)^(+)) supply,mixed nitrogen (N) supply may promote growth of maize seedlings.Previous study suggested that mixed N supply not only increased photosynthesis rate,but also enhanced leaf growth by increasing auxin synthesis to build a large sink for C and N utilization.However,whether this process depends on N absorption is unknown.Here,maize seedlings were grown hydroponically with three N forms (NO_(3)^(-)only,75/25 NO_(3)^(-)/NH_(4)^(+) and NH_(4)^(+) only).The study results suggested that maize growth rate and N content of shoots under mixed N supply was little different to that under sole NO_(3)^(-)supply at 0–3 d,but was higher than under sole NO_(3)^(-)supply at 6–9 d.^(15)N influx rate under mixed N supply was greater than under sole NO_(3)^(-) or NH_(4)^(+) supply at 6–9 d,although NO_(3)^(-) and NH_(4)^(+) influx under mixed N supply were reduced compared to sole NO_(3)^(-) and NH_(4)^(+) supply,respectively.qRT-PCR determination suggested that the increased N absorption under mixed N supply may be related to the higher expression of NO_(3)^(-) transporters in roots,such as ZmNRT1.1A,ZmNRT1.1B,ZmNRT1.1C,ZmNRT1.2 and ZmNRT1.3,or NH_(4)^(+) absorption transporters,such as Zm AMT1.1A,especially the latter.Furthermore,plants had higher nitrate reductase (NR)glutamine synthase (GS) activity and amino acid content under mixed N supply than when under sole NO_(3)^(-) supply.The experiments with inhibitors of NR reductase and GS synthase further confirmed that N assimilation ability under mixed N supply was necessary to promote maize growth,especially for the reduction of NO_(3)^(-) by NR reductase.This research suggested that the increased processes of NO_(3)^(-)and NH_(4)^(+) assimilation by improving N-absorption ability of roots under mixed N supply may be the main driving force to increase maize growth.展开更多
基金supported by the National Basic Research Program of China (2015CB150402)the National Natural Science Foundation of China (31672221 and 31421092)the Science Foundation for Young Scholars of Tobacco Research Institute of Chinese Academy of Agricultural Sciences (2022C03 and 20211302)。
文摘Compared with sole nitrate (NO_(3)^(-)) or sole ammonium (NH_(4)^(+)) supply,mixed nitrogen (N) supply may promote growth of maize seedlings.Previous study suggested that mixed N supply not only increased photosynthesis rate,but also enhanced leaf growth by increasing auxin synthesis to build a large sink for C and N utilization.However,whether this process depends on N absorption is unknown.Here,maize seedlings were grown hydroponically with three N forms (NO_(3)^(-)only,75/25 NO_(3)^(-)/NH_(4)^(+) and NH_(4)^(+) only).The study results suggested that maize growth rate and N content of shoots under mixed N supply was little different to that under sole NO_(3)^(-)supply at 0–3 d,but was higher than under sole NO_(3)^(-)supply at 6–9 d.^(15)N influx rate under mixed N supply was greater than under sole NO_(3)^(-) or NH_(4)^(+) supply at 6–9 d,although NO_(3)^(-) and NH_(4)^(+) influx under mixed N supply were reduced compared to sole NO_(3)^(-) and NH_(4)^(+) supply,respectively.qRT-PCR determination suggested that the increased N absorption under mixed N supply may be related to the higher expression of NO_(3)^(-) transporters in roots,such as ZmNRT1.1A,ZmNRT1.1B,ZmNRT1.1C,ZmNRT1.2 and ZmNRT1.3,or NH_(4)^(+) absorption transporters,such as Zm AMT1.1A,especially the latter.Furthermore,plants had higher nitrate reductase (NR)glutamine synthase (GS) activity and amino acid content under mixed N supply than when under sole NO_(3)^(-) supply.The experiments with inhibitors of NR reductase and GS synthase further confirmed that N assimilation ability under mixed N supply was necessary to promote maize growth,especially for the reduction of NO_(3)^(-) by NR reductase.This research suggested that the increased processes of NO_(3)^(-)and NH_(4)^(+) assimilation by improving N-absorption ability of roots under mixed N supply may be the main driving force to increase maize growth.
