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 1.15.1.1), ascorbate peroxidase (AscPOD, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2) 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 1.1.1.49) showed that the cell had the capacity to produce more NADPH necessary for the detoxification. Stimulation of other enzymes of catabolic pathways (fumarase [EC 4.2.1.2], phosphofructokinase [PFK, EC 2.7.1.1] and phosphoenolpyruvate carboxylase [PEPC, EC 4.1.1.31]), 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.

Sodium salt sensitivity of common oak (Quercus robur L.) was evaluated in hydroponic culture using INRA-Morizet solution. Addition of NaCl to the nutrient solution reduced only length and weight of roots and first flush stems. In contrast, the second flush was properly expanded even in the presence of 40 mM of NaCl in culture medium. Both leaf number and leaf area were not affected by increasing salt concentration in medium culture while this increase induced significant leaf damage especially in first flush leaves. Stem starch storage was reduced only at 40 mM NaCl treatment. Common oak seedlings seemed to be able to better compartmentalize sodium than chloride when the NaCl concentration increased in the medium culture. Chloride presented a lower uptake than sodium. Sodium was preferentially accumulated in roots and this accumulation occurred at the expense of potassium uptake. The decrease of ATP content in leaves of common oak seedlings submitted to NaCl treatments could indicate that it was used for sodium exclusion out of the leaves, especially in second flush leaves. Relationships between growth responses, starch and mineral element distribution in common oak seedlings will be discussed.& k w d : Key words Quercus robur · Growth · Sodium salt stress · Ion partitioning · Starch strorage& b d y :

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