Abstract
Melatonin is effective in enhancing various abiotic stress resistances of plants. However, its underlying mechanisms in drought-resistance in winter wheat (Triticum aestivum L.) is not clear. The goal of this work was to investigate the effect of melatonin on seed germination and to evaluate leaf antioxidant physiology for two wheat varieties. Experiments included 20% PEG, melatonin plus 20% PEG and a control using two contrasting wheat varieties (JM22– drought sensitive and HG35– drought resistant). Melatonin levels were 0, 1, 10, 100 and 300 μmol L-1. Results revealed that 300 μmol L-1 of melatonin alleviated the negative effect of water stress on germination and increased radicle length, radicle number, and plumule length of the germinated seeds. Principal component analysis showed a significant change in amino acid content during germination and this change was dependent on melatonin concentration and the variety. Lysine (Lys) content in wheat seeds under the PEG plus 300 μmol L-1 melatonin treatment increased compared with that of the seeds under PEG alone. There was a significant and positive correlation between Lys content and morphological index of germination. During seedling growth, soluble protein was involved in osmotic adjustment and superoxide dismutase (SOD) activity was increased to mitigate the damage in the cytomembrane of JM 22 leaf under 300 μmol L-1 melatonin plus PEG treatment. The effect of melatonin was dependent on SOD activity increasing significantly for HG35—a drought resistant variety. The results of this work lays a foundation for further studies to determine if melatonin can be economically used to mitigate the impact of dry planting conditions on wheat productivity in North China Plain.
Highlights
Drought is a major abiotic stress that leads to significant yield loss worldwide, and has affected global food security [1, 2]
There was no improvement in germination percentage and germination index of JM22 drought stressed seeds with melatonin at any of the tested concentrations (1, 10, or 100 μM)
Exogenous melatonin plays an important role in improving seed germinations under different abiotic stress conditions such as water deficit [34], high temperature [35], cold [13], and salt stress [36]
Summary
Drought is a major abiotic stress that leads to significant yield loss worldwide, and has affected global food security [1, 2]. There have been few reports on how amino acid affects wheat seeds during germination under drought stress plus melatonin. Priming seed with melatonin at 0.8 mmol L-1 significantly improved germination energy, germination percentage, proline content, and total phenolic content of maize [28] It is still not clear how different concentrations of melatonin affect amino acids during seed germination and the effect of melatonin concentration on antioxidant defense responses of different wheat varieties seedling under water stress. The objectives of this work were (1) to investigate the germination characteristics of two wheat varieties with melatonin at 0, 1, 10, 100, and 300 μmol L-1 concentrations under drought stress; (2) evaluate the changes in amino acid content during germination of wheat seeds under different melatonin levels; and (3) to determine the effective concentration of melatonin in increasing antioxidant activity in wheat. This study will provide information about the mechanism of drought resistance in germination and seedling growth of different wheat varieties treated by melatonin
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