Exogenous calcium alleviates cadmium-induced oxidative stress in rice (Oryza sativa L.) seedlings by regulating the antioxidant defense and glyoxalase systemsCalcium-induced cadmium stress tolerance in rice

The present study was undertaken to investigate the regulatory role of exogenous application of calcium (Ca) in enhancing the antioxidant defense and glyoxalase systems in mitigating cadmium (Cd) stress in rice. Hydroponically grown 14-day-old rice (Oryza sativa L. cv. BRRI dhan29) seedlings were exposed to 0.25 and 0.5 mM CdCl2 alone and in combination with 2.5 mM CaCl2 for 3 days. Exposure to Cd caused chlorosis, leaf rolling symptoms, and growth inhibition. A higher concentration of Cd in the growth medium resulted in higher Cd accumulation, which induced oxidative stress through overproduction of reactive oxygen species (ROS) by disrupting the antioxidant defense system. Cadmium treatment increased the methylglyoxal (MG) level. Calcium supplementation in the Cd-treated growth medium reduced Cd uptake. Application of Ca also significantly increased the (ascorbate) AsA content, increased the activities of superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), monodehydroascorbate reductase (MDHAR), and dehydroascorbate reductase (DHAR) in the antioxidant system, and increased the glyoxalase I (Gly I) and glyoxalase II (Gly II) activities in the glyoxalase system in rice seedlings exposed to both levels of Cd. Exogenous Ca application regulated the antioxidant defense and glyoxalase systems, which reversed overproduced ROS and detoxified MG, which in turn reduced Cd toxicity.