SALINITY, OXIDATIVE STRESS AND ANTIOXIDANT RESPONSES IN SHOOT CULTURES OF RICE

When shoot cultures derived from salt-sensitive Oryza sativa var. Taip ei 309 were grown at 25 degrees C in medium containing 0.35 M NaCl, re sponses to possible oxidative stress in the early stages of exposure w ere observed. Overall levels of Mn-superoxide dismutase activity, Cu, Zn-superoxide dismutase activity and H-2O2 were significantly elevated . After 1 d there was a notable decline in tissue concentrations of GS H and a corresponding increase in GSSG. However, after a further day, concentrations of GSH and GSSG returned to concentrations normally enc ountered in control cultures. Activities of ascorbate peroxidase and c atalase were similar whether the shoots were grown in the presence or absence of NaCl. In contrast, there was an early increase in glutathio ne reductase activity in NaCl-exposed cultures, and no indication of e xtensive increases in lipid peroxidation. Thus although some indicatio ns of oxidative stress accompany exposure of this salt-sensitive rice Variety to salinity, mechanisms appear to exist within its shoot tissu e to permit the tolerance of such oxidative stress.