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Acta Prataculturae Sinica ›› 2022, Vol. 31 ›› Issue (3): 124-135.DOI: 10.11686/cyxb2021011

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Regulation of endogenous isoflavones on alfalfa nodulation and nitrogen fixation and nitrogen use efficiency

Chang-chun TONG(), Xiao-jing LIU(), Yong WU, Ya-jiao ZHAO, Jing WANG   

  1. College of Grassland Science,Gansu Agricultural University,Key Laboratory of Pratacultural Ecosystem,Ministry of Education,Pratacultural Engineering Laboratory of Gansu Province,Sino-US Center for Grazingland Ecosystem Sustainability,Lanzhou 730070,China
  • Received:2020-12-30 Revised:2021-03-10 Online:2022-03-20 Published:2022-01-15
  • Contact: Xiao-jing LIU


This research compared alfalfa varieties “LW6010” with high nitrogen absorption and utilization efficiency and “Longdong” with low nitrogen absorption and utilization efficiency, in order to investigate the relationship between isoflavone concentrations and nodulation, nitrogen fixation and nitrogen use efficiency in alfalfa. The isoflavone concentrations and nitrogen fixation characteristics, together with the expression of isoflavone synthase (IFS) and nodulation signaling pathway (nod) genes of the two alfalfa varieties with contrasting nitrogen use efficiencies were studied at five different nitrogen levels. It was found that the isoflavone content of alfalfa was significantly correlated with the number of nodules, the total nodule weight per plant, the whole plant nitrogen-fixing potential. At lower nitrogen levels, the isoflavone content and nodule number, total nodule weight per plant and nitrogen fixation potential of alfalfa all showed a significant increase. Under nitrogen deficit or over-supply stress, the number of upregulated IFS genes and magnitude of up-regulation in the stems, leaves and roots of the nitrogen-efficient LW6010 variety were greater than those of the nitrogen-inefficient Longdong alfalfa variety, thus promoting high expression of the nod genes and, ultimately, improved nitrogen use efficiency. Therefore, 1) The nodulation and nitrogen fixation of alfalfa is significantly positively correlated with the isoflavone content. When the concentration of exogenous nitrogen decreases, alfalfa is able to increase the isoflavone content in the plant tissues through the expression of different IFS genes in the stems, leaves and roots, thereby stimulating the expression of nod genes to promote nodulation and increase the plant nitrogen fixation potential; 2) The difference in isoflavone content in alfalfa is an important physiological determinant of its nitrogen efficiency. Nitrogen-efficient alfalfa promotes isoflavone synthesis through the high expression of multiple IFS genes under nitrogen stress, thereby stimulating nodulation and nitrogen fixation, thus achieving high nitrogen absorption and nitrogen use efficiency.

Key words: isoflavones, alfalfa, nodulation and nitrogen fixation, nitrogen efficiency, regulation