Salinity, oxidative stress and antioxidant responses in shoot cultures of rice

When shoot cultures derived from salt-sensitive Oryza sativa var. Taipei 309 were grown at 25 degrees C in medium containing 0.35 M NaCl, responses to possible oxidative stress in the early stages of exposure were 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 GSH and a corresponding increase in GSSG. However, after a further day, concentrations of GSH and GSSG returned to concentrations normally encountered in control cultures. Activities of ascorbate peroxidase and catalase were similar whether the shoots were grown in the presence or absence of NaCl. In contrast, there was an early increase in glutathione reductase activity in NaCl-exposed cultures, and no indication of extensive increases in lipid peroxidation. Thus although some indications of oxidative stress accompany exposure of this salt-sensitive rice Variety to salinity, mechanisms appear to exist within its shoot tissue to permit the tolerance of such oxidative stress.