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

Abstract

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. cv. 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.