Nitrate Inhibits Nodule Nitrogen Fixation by Accumulating Ureide in Soybean Plants
Author:
Wang Xuelai1, Zhang Yuchen1, Lian Zhaohui1, Lyu Xiaochen1, Yan Chao1, Yan Shuangshuang1, Gong Zhenping1ORCID, Li Sha2, Ma Chunmei1
Affiliation:
1. College of Agriculture, Northeast Agricultural University, Harbin 150030, China 2. College of Resources and Environment, Northeast Agricultural University, Harbin 150030, China
Abstract
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.
Funder
China Natural Science Foundation Heilongjiang Provincial Natural Science Foundation
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