Melatonin-Induced Resilience Strategies against the Damaging Impacts of Drought Stress in Rice

Drought is a severe abiotic stress that imposes a serious threat to rice productivity. Although previous studies have found that melatonin can promote seed germination, the physiological regulation mechanism of drought tolerance in rice seed germination mediated by exogenous melatonin is still unclear. In order to overcome these challenges, polyethylene glycol 6000 (PEG6000) at concentrations of 20% and 35% was used to simulate osmotic stress. Rice seeds were treated with different concentrations of melatonin (i.e., 0, 20, 100, and 500 &mu:M) to study the effects on germination characteristics, growth and development, superoxide dismutase (SOD) activity, peroxidase (POD) activity, catalase (CAT) activity, malondialdehyde (MDA) content, and soluble protein content. The results showed that the seed soaking treatment using melatonin at a concentration of 100 &mu:M under drought stress effectively promoted the germination rate and improved the biomass of rice seed shoots and roots. Meanwhile, this treatment reduced MDA content to alleviate the oxidative damage of rice seeds caused by drought stress. The two-way ANOVA showed that the effect of single melatonin soaking treatment on rice seed germination was more significant than that of single drought stress and the interaction of drought stress and melatonin (p &lt: 0.05). Using the membership function method, it was shown that the critical gradient of rice seeds under drought stress was 35%, and the critical treatment of interactive treatment was 35% + 100 &mu:M. Through grey correlation analysis, it was found that germination rate (7 d) had the highest grey correlation with melatonin seed soaking treatment to evaluate the mitigation effect of melatonin on drought stress. This study provides a theoretical basis for light and simple cultivation technology for the dry direct seeding of rice.