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 oz one exclusion and detoxification in this protection, spring wheat (Tri ticum aestivum L. cv. Wembley) was grown from seed, in controlled-envi ronment 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), respectiv ely. Cumulative ozone dose to the mesophyll and antioxidant status wer e determined throughout flag leaf development. Catalase activity corre lated with rates of photorespiration and declined in response to eleva ted [CO2] and/or [O-3]. Superoxide dismutase activity was not signific antly affected by either condition. Neither ascorbate nor glutathione content was enhanced by elevated [CO2]. In wheat, at moderately elevat ed [O-3], our results show that stomatal exclusion plays a major role in the protective effect of elevated [CO2] against O-3 damage.