Glucose-6-Phosphate Dehydrogenase Is Involved in the Tolerance of Soybean Seedlings to Low Nitrogen Stress

Abstract

Nitrogen (N) deficiency affects plant growth and crop yield. In this study, we investigated the role of glucose-6-phosphate dehydrogenase (G6PDH) in response to N availability in three soybean cultivars, JINDOU 19 (JD19), LONGHUANG 3 (LH3), and LONGDOU 2 (LD2), that have different tolerances to low-N stress. The results showed that the leaf area and primary root length of JD19 and LH3 were greater than that of LD2 under low-N stress, suggesting that the growth of JD19 and LH3 were impaired less than LD2, and thus are more tolerant to low-N stress than LD2 is. Interestingly, the G6PDH expression showed different degrees of change in these soybean cultivars under low-N conditions, and the G6PDH activity in JD19 and LH3 was higher than that in LD2. When G6PDH was inhibited by glucosamine (GlcN), the contents of malondialdehyde (MDA) and H2O2 were dramatically increased under low-N stress. Meanwhile, the activities of N metabolism-related enzymes were inhibited. These results indicate that G6PDH is involved in the tolerance of soybean cultivars to low-N stress through affecting the N metabolism. Furthermore, under low-N conditions, the contents of NADP+ and reduced glutathione (GSH) in JD19 and LH3 were increased more than that in LD2. In contrast, the activity of the plasma membrane (PM), NADPH oxidase, and the NADPH content in JD19 and LH3 were lower than that in LD2. In conclusion, G6PDH reduces the accumulation of ROS in plant cells by modulating NADPH/NADP+ and GSH levels to maintain the growth of soybeans under low-N conditions.