Effects of External Calcium on Activities of Antioxidant Enzymes and Membrane Lipid Peroxidation in Rice Seedlings under Nickel Stress

In order to explore the possible physiological mechanisms of calcium involved in improving adaptation to nickel stress in plants,the effects of external calcium(Ca2+)on the activities of superoxide dismutase(SOD),catalase(CAT),peroxidase(POD)and ascorbate peroxidase(APX),the contents of H2O2 and malondialdehyde(MDA),and electrolyte leakage of leaf tissues were investigated in nickel-stressed rice seedlings.Under 0.1 mmol/L nickel(Ni2+)treatment,the activities of SOD,CAT and APX in rice leaf tissues were significantly decreased,while the activity of POD was obviously enhanced.Moreover,nickel treatments significantly increased the contents of H2O2 and MDA in rice leaf tissues,suggesting oxidative damage and membrane peroxidation occurred in nickel-treated leaf tissues.External calcium promoted the activities of SOD,CAT,APX and POD,but reduced considerably H2O2 and MDA contents and permeability of cell membrane in leaf tissues during the stress period.In addition,the activities of CAT,SOD,POD and APX in 10 mmol/L Ca2+-supplemented leaf tissues were higher,and H2O2 and MDA contents were lesser than those in 5 mmol/L Ca2+ under the nickel stress.It was suggested that one of the mechanisms that external calcium enhanced the tolerance to nickel toxicity in rice seedlings was mediated by improving scavenging of active oxygen species and maintaining the integrity of cell membrane under nickel stress.