AMELIORATION OF OZONE-INDUCED OXIDATIVE DAMAGE IN WHEAT PLANTS GROWN UNDER HIGH-CARBON DIOXIDE - ROLE OF ANTIOXIDANT ENZYMES

O-3-induced changes in growth, oxidative damage to protein, and specif ic activities of certain antioxidant enzymes were investigated in whea t plants (Triticum aestivum L. cv Roblin) grown under ambient or high CO2. High CO2 enhanced shoot biomass of wheat plants, whereas O-3 expo sure decreased shoot biomass. The shoot biomass was relatively unaffec ted in plants grown under a combination of high CO2 and O-3. O-3 expos ure under ambient CO2 decreased photosynthetic pigments, soluble prote ins, and ribulose-1,5-bisphosphate carboxylase/oxygenase protein and e nhanced oxidative damage to proteins, but these effects were not obser ved in plants exposed to O-3 under high CO2. O-3 exposure initially en hanced the specific activities of superoxide dismutase, peroxidase, gl utathione reductase, and ascorbate peroxidase irrespective of growth i n ambient or high CO2. However, the specific activities decreased in p lants with prolonged exposure to O-3 under ambient CO2 but not in plan ts exposed to O-3 under high CO2. Native gels revealed preferential ch anges in the isoform composition of superoxide dismutase, peroxidases, and ascorbate peroxidase of plants grown under a combination of high CO2 and O-3. Furthermore, growth under high CO2 and O-3 led to the syn thesis of one new isoform of glutathione reductase. This could explain why plants grown under a combination of high CO2 and O-3 are capable of resisting O-3-induced damage to growth and proteins compared to pla nts exposed to O-3 under ambient CO2.