Chinese Bulletin of Botany ›› 2021, Vol. 56 ›› Issue (4): 391-403.DOI: 10.11983/CBB21037


Effects of Nitrogen Application on Nitrogen Fixation Capacity and GmLbs Expression in Soybean

Mengke Du, Wenting Lian, Xiao Zhang, Xinxin Li*()   

  1. Root Biology Center, Fujian Agriculture and Forestry University, Fuzhou 350002, China
  • Received:2021-02-13 Accepted:2021-05-07 Online:2021-07-01 Published:2021-06-30
  • Contact: Xinxin Li

Abstract: The nitrogen fixation efficiency of symbiotic nodules is tightly regulated by external nitrogen (N). In addition to nitrogenase activity, the leghemoglobin (Lb) amount is vital index contributing to N2 fixation. To determine the effect of environmental N level on biological nitrogen fixation, soybean plants were inoculated with rhizobia for 30 d under low N condition (0.53 mmol·L-1), then transplanted to hydroponic culture solution with relatively higher N concentrations, including 5.3, 10, 20, 30, and 40 mmol·L-1 for 7 d, respectively. Lb concentration, nitrogenase activity and bacteroid development status were measured. Nodule displayed changed color from red to green with increasing N concentrations. Consistently, the red Lb concentration gradually declined with increased green Lb concentration. Moreover, the nitrogenase activity, infected cell number and area in nodules were all significantly decreased, suggesting that changes in Lb forms caused by excess N are closely associated with nitrogen fixation capacity. Bioinformatics and public expression profile data displayed that four symbiosis-associated Lbs, including GmLb1, GmLb2, GmLb3, and GmLb4 are the major Lb genes in soybean nodulation. These four GmLbs belong to the same clade of phylogenetic tree. Further analysis on the transcripts of GmLb1-4 in response to N showed that the expression levels of GmLb1-4 were all significantly inhibited by high N. This study services as a reference for future studies in understanding the underlying mechanisms of N-triggered nodule senescence as well as BNF application in agriculture.

Key words: biological nitrogen fixation, GmLbs, leghemoglobin, nitrogen concentration, soybean