Melatonin promotes plant growth by increasing nitrogen uptake and assimilation under nitrogen deficient condition in winter wheat

Melatonin (MEL) has been widely reported to be beneficial to plant growth and development, but few studies have combined investigations of the performance and function of MEL with detailed physiologically based analyses of nitrogen (N) uptake and metabolism in staple crops. In this study, the effect of MEL application on winter wheat seedling growth and grain yield were investigated in hydroponic and pot experiments at different N levels. The result showed that application of 1 μM MEL in hydroponic solution significantly improved the wheat seedling growth under both N sufficient and deficient conditions, but the effect of MEL on promoting seedling growth was prominent under N deficient condition. Meanwhile, MEL-treated plants maintained higher N contents and nitrate nitrogen levels in shoot under N deficient condition, and also maintained higher nitrate nitrogen levels in root. Further investigation showed that nitrate reductase (NR) and glutamine synthetase (GS) activities were higher in MEL-treated plants than that of MEL-untreated plants under N deficiency. The N absorption calculated based on N contents and biomass showed that MEL could promote the N absorption under N deficient condition. In pot experiment, pre-soaking of seeds with 100 μM MEL enhanced per-plant yield by 16% under N sufficient condition and 23% under N deficient condition. Taken together, the results of this study indicate that MEL is involved in promoting N uptake and assimilation through up-regulating the activities of N uptake and metabolism related enzymes and, ultimately, promotes the plant growth and yield, especially under N deficient condition.