Exogenous Application of Methyl Jasmonate Lowers the Effect of Cadmium-induced Oxidative Injury in Rice Seedlings

Rice seedlings grown under 50 μM cadmium alone or in combination with 5 μM methyl jasmonate were investigated for Cd-induced oxidative injury at 3, 7 and 10 days of treatment. MeJA treatments alone did not have any significant change in antioxidant enzyme activities or levels of H2O2 and O2(·-) in roots/shoots, as compared to controls during 3-10 days. The Cd-stressed plants When supplemented with exogenous MeJA revealed significant and consistent changes in activities of antioxidant enzymes CAT, SOD, POD and GR paralleled with an increased GSH-pools than that in plants subjected to Cd-stress alone. Synthesis of GSH driven by increasing demand for GSH in response to Cd-induced oxidative stress in rice was evident. Increased activity of LOX under Cd-stress was noted. Results suggest enhanced Cd-tolerance, lowered Cd(2+) uptake, an improved membrane integrity and 'switching on' of the JA-biosynthesis by LOX in the Cd-stressed rice roots/shoots exposed to MeJA. Exposure to MeJA improved antioxidant response and accumulation of antioxidants which perhaps lowered the Cd-induced oxidative stress in rice. It is this switching on/off of the JA-biosynthesis and ROS mediated signal transduction pathway involving glutathione homeostasis via GR which helps MeJA to mitigate Cd-induced oxidative injury in rice.