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 [O-3]. To investigate the role of ozone exclusion and detoxification in this protection, spring wheat (Triticum aestivum L. cv. Wembley) was grown from seed, in controlled-environment chambers, under reciprocal combinations of [CO2] at 350 or 700 mu mol mol(-1) and [O-3] 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 [O-3]. 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 [O-3], our results show that stomatal exclusion plays a major role in the protective effect of elevated [CO2] against O-3 damage.