PHYSIOLOGICAL MECHANISM OF MELATONIN REGULATION IN SOYBEANS UNDER ALUMINUM STRESS

Aluminum (Al) is one of the main toxicants that affect crop growth in acidic soils. Melatonin (MT) is an important steroidal hormone that can increase the plant's stress resistance. However, the regulatory mechanism of Al stress in plants remains unclear. This study investigated the effects of MT on the growth, antioxidant system, and photosynthesis of soybean seedlings under Al stress. Results showed that, compared with the control group, Al stress resulted in lower superoxide dismutase, catalase, and peroxidase activity, increased accumulation of malondialdehyde in the leaves of soybean seedlings, increased membrane permeability, and significant decrease in the photosynthetic rate, transpiration rate, and stomatal conductance of seedlings. The fresh weight and dry weight of the seedlings decreased by 22.0% and 18.1%, respectively, and the growth was significantly inhibited. Foliar application of MT could effectively increase the anti-oxidative enzyme activity of soybean seedlings under Al stress, reduce the degree of membrane lipid peroxidation, relieve Al damage to chloroplast PSII, enhance its photosynthetic performance, and significantly increase the dry weight and fresh weight of the seedlings. Consequently, the damage caused by Al stress was effectively alleviating and the growth of seedlings was promoted.