The aim of this study was to examine possible alterations in the metabolism of rice plants (Oryza sativa L.) that were exposed to high salt concentrations. BRS Ligeirinho seeds were sown, and the plants were grown in a greenhouse. At 14 days following sowing, the plants were alternately irrigated with a nutrient solution and water containing 0, 150 and 300 mM NaCl. After 30 days, the leaves and roots were collected, and the levels of proline, photosynthetic pigments, total protein, hydrogen peroxide, lipid peroxidation and the activities of the antioxidant enzymes superoxide dismutase, catalase and ascorbate peroxidase were analysed. There was a gradual increase in the levels of proline, total protein, hydrogen peroxide and lipid peroxidation with increasing salt concentrations in the irrigation water. The synthesis of photosynthetic pigments increased until the NaCl concentration reached 150 mM, after which the activities of the antioxidant enzymes decreased. These results suggest that proline may have protective effects against protein degradation and that carotenoids may aid in the protection of chlorophyll. Moreover, although, antioxidant enzymes were shown to possess low levels of activity, a large proportion of the hydrogen peroxide that is produced is preferentially directed towards lipid peroxidation.
Key words: Oryza sativa L., salinity, oxidative stress, reactive oxygen species, lipid peroxidation, chlorophyll.