Seed priming with melatonin coping drought stress in rapeseed by regulating reactive oxygen species detoxification: Antioxidant defense system, osmotic adjustment, stomatal traits and chloroplast ultrastructure perseveration

Water stress encumbers the rapeseed growth and development primarily by oxidative alteration to biological membranes and interrupted tissue water status. Seedling tolerance to water stress is vital for better crop development through the entire period under drought stress condition. The enhancement of plant stress tolerance due to melatonin application is already known; however, the specific underlying mechanisms are still not fully understood. The current study was done to investigate the effect of melatonin-priming on rapeseed germination and subsequent seedling growth under PEG-6000 simulated drought stress. Drought stress significantly inhibited germination and seedling growth, led to oxidative stress from excessive H2O2 generation, and reduced the chlorophyll content. Melatonin-priming alleviated the oxidative damage and the amount of chlorophyll reduction in rapeseed seedlings under the drought stress. The stomatal traits such as number, stomatal length and width were greatly improved in melatonin-primed treatment. Melatonin-priming also preserved the chloroplast structure, maintained cells expansion and strengthened the cell wall in response to drought stress. The results revealed that the ameliorative effects of melatonin-priming may be ascribed to enhancement of antioxidant enzymes activities, increase in the content of non-enzymatic antioxidants, and increase in the amounts of osmo-protectants. The present data suggest that priming seeds with melatonin can be a prime strategy regarding the development of crop drought resistant in crop production.