Abstract:

This study aims to investigate the alleviating effects of exogenous brassinolide (BR) on the salt stress in growth of kenaf seedlings and to elucidate the underlying physiological mechanisms. The cultivar ‘Zhonghongma 21’, developed by the Institute of Bast Fiber Crops, Chinese Academy of Agricultural Sciences, was used as the experimental material. Salt stress was simulated under hydroponic conditions using 125 mmol/L NaCl solution, and four BR concentrations (0.025, 0.05, 0.075, and 0.1 mg/L) were applied. The results showed that exogenous BR effectively alleviated the inhibitory effects of salt stress on kenaf seedlings compared with the NaCl treatment alone, and the 0.05 mg/L BR treatment exhibited the most significant alleviating effect. Compared with the NaCl treatment, the 0.05 mg/L BR treatment significantly increased plant height, root length, fresh weight, and dry weight by 74.1%, 57.6%, 88.6%, and 92.2%, respectively (P<0.05), indicating that BR promoted biomass accumulation and morphological development in kenaf seedlings under salt stress. In addition, the relative chlorophyll content and soluble sugar content increased by 44.0% and 58.3%, respectively, which contributed to maintaining cellular osmotic balance and photosynthetic efficiency. The activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) increased by 68.4%, 241.9%, and 100.6%, respectively, compared with the NaCl treatment. Meanwhile, the accumulation of hydrogen peroxide (H₂O₂) and superoxide anion (O₂·^-) was reduced, accompanied by significant decreases in malondialdehyde (MDA) content and relative electrical conductivity. These findings indicate that exogenous BR can enhance the salt tolerance of kenaf seedlings by coordinately regulating accumulation of osmotic adjustment substance and the antioxidant enzyme system.

Key words: kenaf, salt stress, brassinolide, salt tolerance, osmotic adjustment, antioxidant enzyme system, seedling growth