GENETIC-CONTROL OF RESPONSES TO INTERACTING TROPOSPHERIC OZONE AND CO2 IN POPULUS-TREMULOIDES

We exposed trembling aspen (Populus tremuloides Michx.) clones differi ng in tropospheric ozone (O-3) tolerance in various open-top chamber s tudies for three growing seasons, and examined the effects of O-3, CO2 , and O-3 + CO2 on growth and physiological processes. Ozone in the ra nge of 80 ppm hr (Sum 00) per growing season decreased height, diamete r, and stem and leaf biomass slightly in a tolerant clone but severely in a sensitive clone. Elevated CO2 (150 ppm over ambient) did not com pensate for the O-3 effects. Antioxidant enzyme analysis showed elevat ed SOD levels in the tolerant clone but not in the sensitive clone fol lowing O-3 exposure. Northern blot analysis indicated that the chlorop lastic and cytosolic Cu/Zn SOD's were significantly increased in respo nse to O-3 in the tolerant but not the sensitive clone. Currently, we are conducting molecular analysis to determine the functional signific ance of SOD's in regulating O-3 tolerance in aspen. (C) 1997 Elsevier Science Ltd.