Harnessing methyl jasmonate signalling to counteract salt stress in papaya (Carica papaya L.) – A physiological and biochemical perspective

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Salinity is a critical abiotic constraint on papaya cultivation in salt-prone regions, as papaya is highly sensitive to ionic and osmotic stress. This study investigated the role of exogenous methyl jasmonate (MeJA) in mitigating salt-induced physiological and biochemical impairments in papaya seedlings. Uniform seedlings of cv. Red Lady plants were exposed to 100 mM NaCl to simulate moderate salinity (7.0 dS m-¹) and subsequently treated with foliar MeJA @ 0, 25, 50, 75, and 100 µM under controlled greenhouse conditions. Salinity significantly reduced chlorophyll content, relative leaf water content (RLWC), and antioxidant enzyme activities, accompanied by elevated proline and malondialdehyde (MDA) accumulation. The application of MeJA significantly alleviated the adverse effects of salinity, with the 75 µM concentration showing the most effectiveness. This particular concentration facilitated the stabilization of chlorophyll (resulting in an 11.4% increase in total chlorophyll), RLWC (an 83.1% increase), and the accumulation of soluble sugars and phenolic compounds, concurrently elevating the activities of superoxide dismutase (42.6%), catalase, and ascorbate peroxidase. Furthermore, the application of MeJA corresponded with a reduction in MDA levels (26.6%), suggesting a decrease in lipid peroxidation and an enhancement of membrane integrity. Conversely, a higher concentration of MeJA (100 µM) caused a slight slowdown in growth, which highlights the biphasic nature of jasmonate signaling. In conclusion, applying MeJA at a moderate concentration (75 µM) effectively triggered defense mechanisms, stabilized the balance of cellular redox reactions, and improved salinity tolerance in papaya seedlings.