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

Elevated [CO ] has been shown to protect photosynthesis and growth of wheat against moderately elevated [O ]. 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 [CO ] at 350 or 700 μmol mol and [O ] peaking at < 5 or 60 nmol mol , 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 [CO ] and/or [O ]. Superoxide dismutase activity was not significantly affected by either condition. Neither ascorbate nor glutathione content was enhanced by elevated [CO ]. In wheat, at moderately elevated [O ], our results show that stomatal exclusion plays a major role in the protective effect of elevated [CO ] against O damage.