Growth under elevated CO(2) ameliorates defenses against photo-oxidative stress in poplar (Populus alba x tremula).

To test the hypothesis that growth-CO(2) concentrations affect stress susceptibility, leaves of poplar trees (Populus alba x tremula) grown under ambient or about twofold ambient CO(2) concentrations were subjected to chilling temperatures at high light intensities or were exposed to paraquat. Photosynthesis was less diminished and electrolyte leakage was lower in stressed leaves from poplar trees grown under elevated [CO(2)] as compared with those from ambient [CO(2)]. Severe stress caused pigment and protein degradation but to a lower extent in leaves from elevated as compared with those from ambient [CO(2)]. The protection was accompanied by rapid induction of superoxide dismutase activities (EC 1.15.1.1). Ascorbate and glutathione-related detoxification systems as well as catalase (EC 1.11.1.6) activities were less resistant than superoxide dismutases and declined in stress-exposed leaves from poplars grown under elevated [CO(2)] to a similar extent as in those from trees grown under ambient [CO(2)]. These results suggest that the CO(2)-mediated amelioration of stress was confined to SOD and limited since the destruction of H(2)O(2)-degrading systems was not prevented.