Abstract: We examined the effects of foliar spraying of 100 μmol·L^-1 melatonin on carbon and nitrogen metabolism of seedlings of indica-japonica hybrid rice “Yongyou 1540” under salt stress. Potting soil with NaCl concentration of 16.3 mmol·kg^-1 was used as the control, and NaCl was supplemented to 100 mmol·kg^-1 as salt stress. The results showed that, compared with the control, salt stress inhibited rice growth, carbon and nitrogen metabolism, and the effects were much stronger with the prolongation of stress time. The contents of carbohydrates and osmotic adjustment substances and the activities of antioxidant enzymes were increased on the 10th day of stress, and they were lower than that of CK on the 24th day. The contents of indoleacetic acid (IAA), gibberellin (GA₃), and trans-zeatin  (ZR) decreased, and that of abscisic acid (ABA) and melatonin (MT) increased on the 10th day of stress. Melatonin treatment enhanced the carbon and nitrogen metabolism capacity and antioxidant enzyme activity of seedlings under salt stress, as well as increased MT, IAA, GA₃ and ZR contents, and reduced ABA content. Our results indicated that exogenous melatonin can improve carbon and nitrogen metabolism and promote rice seedling growth under salt stress, and enhance their resistance to salt stress.

Key words: salt stress, melatonin, carbon and nitrogen metabolism, hormone, rice.