Exogenous Methyl Jasmonate Mitigates the Oxidative Damage in Cucumber Seedlings Subjected to Water Stress

Drought tolerance is considered to be an essential element for cucumber (Cucumis sativus) production in arid climates, and it has been suggested that higher antioxidant activity could mitigate the oxidative damage caused by water stress. The study was aimed to investigate whether the exogenous application of methyl jasmonate (MJ) accelerates antioxidant activity and the resulting drought tolerance potential of cucumber seedlings. Cucumber seedlings (cv. Sambar), which are reported to have moderate drought tolerance were grown in greenhouse environment to evaluate the effects of MJ on the concentration of organic osmolytes (proline, glycinebetaine, amino acids) and antioxidant activity superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), guaiacol peroxidase, and ascorbate peroxidase (APX).  MJ was applied as a foliar spray (spray with water as control and 4 mM MJ) and plants received irrigation to 50% (drought stress) and 75% (control) relative water contents RWC. The seedlings submitted to water stress showed a significant elevation in the leaf proline, glycinebetaine, amino acids, SOD, POD, CAT, GPX, and APX activities. However, exogenous MJ reduced the lipid peroxidation (LPO) and improved the membrane stability index (MSI) of water stressed seedlings. It was concluded that exogenous application of MJ as a foliar spray strengthened the antioxidant system and enhanced the osmotic adjustment potential of water stressed cucumber seedlings therefore potentially alleviating the oxidative damage caused by water stress.