Melatonin Alleviates Abscisic Acid Deficiency Inhibition on Photosynthesis and Antioxidant Systems in Rice under Salt Stress

Melatonin and abscisic acid, as major plant hormones, play important roles in the physiological and biochemical activities of crops, but the interaction between the two under salt stress is not yet clear. This study investigated the endogenous levels of melatonin and abscisic acid in rice by using exogenous melatonin, abscisic acid, and their synthetic inhibitors, and examined their interactions under salt stress. The research results indicate that melatonin and abscisic acid can improve rice salt tolerance. Melatonin alleviated the salt sensitivity caused by abscisic acid deficiency, increased antioxidant enzyme activity and antioxidant content in rice treated with abscisic acid synthesis inhibitors, and reduced total reactive oxygen species content and thiobarbituric acid reactive substance accumulation. Melatonin also increased the activity of key photosynthetic enzymes and the content of photosynthetic pigments, maintaining the parameters of photosynthetic gas exchange and chlorophyll fluorescence. In summary, melatonin alleviated the effects of abscisic acid deficiency on photosynthesis and antioxidant systems in rice and improved salt tolerance. This study is beneficial for expanding the understanding of melatonin regulation of crop salt tolerance.