Spermine (Spm) counteracted the adverse effects of salt-induced oxidative stress in leaves of rice (Oryza sativa L.) seedlings by reducing lipid peroxidation and increasing activities of antioxidative enzymes. Seedlings (25 days old) of two rice cultivars (salt-sensitive IR-28 and salt-tolerant CSR-10) were exposed to 50 and 100 mM salt stress with or without 0.1 and 1 mM Spm for 10 days. Salt stress significantly enhanced oxidative stress as measured by increase in superoxide (O-.(2) (-)) level and H2O2 content, lipid peroxidation [MDA, and lipoxygenase (LOX) activity] in both the rice cultivars; however, the increase was more pronounced in IR-28. The activities of antioxidant enzymes viz. catalase (CAT) and ascorbate peroxidase (APX) decreased under salt stress while the activities of superoxide dismutase (SOD), peroxidase (POX) and glutathione reductase (GR) increased. Spermine treatment could to some extent alleviate the detrimental effects of salinity by reducing oxidative stress, lipid peroxidation, and increasing SOD, CAT, POX, APX and GR activities and 0.1 mM Spm treatment was more effective. Isozyme profile of these antioxidant enzymes revealed reduction in the intensity of variants of SOD (SOD2 and SOD3 in IR-28 and SOD3 in CSR-10) and one of POX (POX2) under saline conditions. The Spm treatment resulted in increase in the intensity of these bands. It is inferred that application of Spm reduces the effect of salt stress through the regulation of stress related components such as oxidative stress and antioxidative system.
