We have studied the effects of ozone, carbon dioxide and ozone combined with carbon dioxide fumigations on catabolic and detoxification pathways in spruce (Picea abies[L.] Karst.) needles. The results obtained showed an increase in the activities of three enzymes involved in the detoxification pathway, superoxide dismutase (SOD, EC 18.104.22.168), ascorbate peroxidase (AscPOD, EC 22.214.171.124) and glutathione reductase (GR, EC 126.96.36.199) when trees were exposed to ozone and to ozone-carbon dioxide treatments. In these two treatments, the fraction of SOD activity due to the chloroplastic isoform was increased (1.5-fold). In the needles of trees exposed to ozone and to ozone-carbon dioxide fumigation, an increase in the activities of glucose-6-phosphate dehydrogenase (G-6-PDH, EC 188.8.131.52) showed that the cell had the capacity to produce more NADPH necessary for the detoxification. Stimulation of other enzymes of catabolic pathways (fumarase [EC 184.108.40.206], phosphofructokinase [PFK, EC 220.127.116.11] and phosphoenolpyruvate carboxylase [PEPC, EC 18.104.22.168]), was also observed making it possible for the cell to provide the reducing power necessary for detoxification as well as energy and carbon skeletons involved in the repair processes.
When carbon dioxide alone was applied, no effects could be detected on these enzyme activities. However, when carbon dioxide was combined with ozone, the effect of ozone on trees was less than that induced by ozone alone, suggesting that elevated atmospheric carbon dioxide concentrations may to some extent protect plants from ozone injury.