EFFECTS OF EXOGENOUS ABSCISIC ACID ON SALT TOLERANCE OF WATERMELON SEEDLINGS UNDER NaCl STRESS

Effects of exogenous abscisic acid (ABA) treatment on growth, chlorophyll fluorescence parameters, and antioxidant enzyme activities of watermelon seedlings under NaCl stress were investigated in this study to explore physiological mechanism of ABA-induced salt tolerance response of watermelon. Results showed that NaCl stress significantly reduced the growth and photosynthetic efficiency of watermelon seedlings and affected activities of antioxidant enzymes. ABA treatment at a certain concentration significantly reduced salt injury index and increased fresh and dry weights of watermelon seedlings under NaCl stress. The maximum photosynthetic efficiency, actual photosynthetic efficiency, relative electron transport rate, and photochemical quenching of photosystem II of watermelon seedlings under NaCl stress increased first and then decreased with the increase of ABA concentration, while non-photochemical quenching, quantum yield of regulated energy dissipation, and quantum yield of non-regulated energy dissipation showed the opposite trend. ABA treatment increased activities of superoxide dismutase, catalase, and peroxidase in plants and reduced the content of malondialdehyde. Treatment with ABA concentrations of 1 and 5 mg center dot L-1 demonstrated an enhanced effect that can improve salt tolerance and effectively alleviate injury of watermelon seedlings under NaCl stress.