Enhanced ozone-tolerance in wheat grown at an elevated CO₂ concentration: ozone exclusion and detoxification

Elevated [CO₂ ] has been shown to protect photosynthesis and growth of wheat against moderately elevated [O₃ ]. To investigate the role of ozone exclusion and detoxification in this protection, spring wheat (Triticum aestivum L. ev. Wembley) was grown from seed, in controlled-environment chambers, under reciprocal combinations of [CO₂ ] at 350 or 700 μmol mol^-1 and [O₃ ] peaking at < 5 or 60 nmol mol^-1 , respectively. Cumulative ozone dose to the mesophyll and antioxidant status were determined throughout flag leaf development. Catalase activity correlated with rates of photorespiration and declined in response to elevated [CO₂ ] and/or [O₃ ]. Superoxide dismutase activity was not significantly affected by either condition. Neither ascorbate nor glutathione content was enhanced by elevated [CO₂ ]. In wheat, at moderately elevated [O₃ ], our results show that stomatal exclusion plays a major role in the protective effect of elevated [CO₂ ] against O₃ damage.