Melatonin improves nitrogen metabolism during grain filling under drought stress

Drought affects the normal growth and development of soybeans. Melatonin reportedly alleviates drought stress-induced growth inhibition and plant injury, thus, its foliar application presumably has considerable potential in agriculture. However, few studies have investigated the mechanism responsible for its effects on soybean nitrogen metabolism. In this study, pot culture and plant physiological detection, qPCR, and other methods were used for analysis. The purpose of this study was to explore the effects of melatonin and melanin on glutathione metabolism. The results showed that drought stress led to an increase in soluble protein and proline content, concomitantly with a decrease in the activity of nitrogen metabolism-related key enzymes, an increase in inorganic nitrogen content, and a reduction in nitrogen accumulation and transport. Exogenous melatonin application under drought stress significantly increased the expression of key genes involved in nitrogen metabolism and the activity of key enzymes including, GOGAT, NR, Gs and GDH. Enhanced enzyme activity promotes the conversion of nitrate nitrogen in plants, increases proline, soluble protein, and ureide contents, and, consequently, nitrogen accumulation. Altogether, these changes were conducive to greater nitrogen assimilation and transport. Therefore, under drought stress, melatonin application upregulated key genes involved in nitrogen metabolism, thereby enhancing the activity of related enzymes and restoring growth, stable biomass production.