Methyl jasmonate (MeJA) enhances salt tolerance of okra (Abelmoschus esculentus L.) plants by regulating ABA signaling, osmotic adjustment substances, photosynthesis and ROS metabolism

Methyl jasmonate (MeJA), as a plant growth regulator, which is involves in many morphological and physiological processes, plays an important role in defense systems of plants under stress conditions. However, the roles of physiological and biochemical mechanisms of enhancing salt tolerance of okra plants based on application of MeJA is poorly understood. In this study, the application of the investigated 50 μM MeJA significantly improved salt tolerance of okra plants based on the germination rates and culture pot experiment under salt stress. Based on optimal concentration of MeJA inducing salt tolerance of okra plants, application of 5 mM diphenyleneiodonium (NADPH oxidase inhibitor, DPI) and 50 μM MeJA + 5 mM DPI, respectively, significantly increased salt tolerance of okra plants. Assays on the content of component matter indicated the significant increases of JA, ABA, proline, soluble protein, soluble sugar, photosynthetic pigment and relative water, glutathione (GSH) and ascorbic acid (AsA) content and the significant decreases of hydrogen peroxide (H2O2), superoxide radicals (O2−) and malondialdehyde (MDA) content and electrolyte leakage rates were observed in okra plants with 50 μM MeJA under salt stress. The activities of superoxide dismutase (SOD), glutathione peroxidase (GPX), catalase (CAT), glutathione reductase (GR), ascorbate peroxidase (APX) and peroxidase (POD) related to ROS scavenging were also enhanced in okra plants by applied MeJA under salt stress. Furthermore, the marked decreases of H2O2, O2- and MDA content, and the significant increases of CAT, GR and APX activities and GSH and ASA content involved in ASA-GSH cycle were observed in MeJA-okra, DPI-okra and MeJA+DPI-okra plants under salt stress. H2O2 acted a toxic accumulation of ROS rather than as a second messenger for signal transduction in okra plants. These results demonstrate that exogenous MeJA increases the accumulation of JA, ABA and proline, which enhances salt tolerance of okra plants, by regulating osmotic balance and protecting membrane integrity and photosynthesis and activating ROS scavenging system. As a conclusion, treating okra plants with 50 μM MeJA could alleviate the harmful effects of abiotic stresses.