Genetic control of responses to interacting tropospheric ozone and CO2 in Populus tremuloides

We exposed trembling aspen (Populus tremuloides Michx.) clones differing in tropospheric ozone (O-3) tolerance in various open-top chamber studies for three growing seasons, and examined the effects of O-3, CO2, and O-3 + CO2 on growth and physiological processes. Ozone in the range of 80 ppm hr (Sum 00) per growing season decreased height, diameter, and stem and leaf biomass slightly in a tolerant clone but severely in a sensitive clone. Elevated CO2 (150 ppm over ambient) did not compensate for the O-3 effects. Antioxidant enzyme analysis showed elevated SOD levels in the tolerant clone but not in the sensitive clone following O-3 exposure. Northern blot analysis indicated that the chloroplastic and cytosolic Cu/Zn SOD's were significantly increased in response to O-3 in the tolerant but not the sensitive clone. Currently, we are conducting molecular analysis to determine the functional significance of SOD's in regulating O-3 tolerance in aspen. (C) 1997 Elsevier Science Ltd.