硝酸盐抑制大豆固氮的机制(GlycinemaxL.)尚未完全了解。酰脲在大豆植物组织中的积累可能通过反馈途径调节固氮能力。在这项研究中,通过嫁接制备的单侧结瘤双根大豆在沙培中生长。它们被去除结瘤的侧根,并且向未结瘤的侧根给予硝酸盐供应或不供应3天(实验I)。此外,它们向未结瘤的侧根接受硝酸盐供应1-14天(实验II)。结果表明,硝酸盐的供应增加了大豆芽中天冬酰胺和酰脲的水平(实验I)。在实验二,结节干重,结节数,结节固氮酶活性,硝酸盐供应3、7和14天后,结节尿酸氧化酶活性显着下降。硝酸盐供应1、3和7天后,芽和结节中的尿素含量增加,但硝酸盐供应14天后下降。尿酸氧化酶活性与固氮酶活性呈显著正相关。因此,我们推断硝酸盐的供应增加了大豆芽中的天冬酰胺含量,可能抑制脲降解,诱导了大豆芽和根瘤中脲的积累,and,反过来,反馈抑制了结节固氮。此外,尿酸氧化酶活性可用于评估结节的固氮能力。
The mechanism by which nitrate inhibits nitrogen fixation in soybean (Glycine max L.) is not fully understood. Accumulation of ureide in soybean plant tissues may regulate the nitrogen fixation capacity through a feedback pathway. In this study, unilaterally nodulated dual-root soybeans prepared by grafting were grown in sand culture. They were subjected to the removal of the nodulated side roots, and were given either nitrate supply or no supply to the non-nodulated side roots for 3 days (experiment I). Additionally, they received nitrate supply to the non-nodulated side roots for 1-14 days (experiment II). The results showed that nitrate supply increased the levels of
asparagine and ureide in soybean shoots (Experiment I). In Experiment II, nodule dry weight, nodule number, nodule nitrogenase activity, and nodule urate oxidase activity decreased significantly after 3, 7, and 14 days of nitrate supply. Ureide content in the shoots and nodules increased after 1, 3, and 7 days of nitrate supply, but decreased after 14 days of nitrate supply. There was a significant positive correlation between urate oxidase activity and nitrogenase activity. Hence, we deduced that nitrate supply increased the
asparagine content in soybean shoots, likely inhibiting ureide degradation, which induced the accumulation of ureide in soybean shoots and nodules, and, in turn, feedback inhibited the nodule nitrogen fixation. In addition, urate oxidase activity can be used to assess the nitrogen fixation capacity of nodules.