EFFECTS OF OZONE AND MILD DROUGHT STRESS ON TOTAL AND APOPLASTIC GUAIACOL PEROXIDASE AND LIPID-PEROXIDATION IN CURRENT-YEAR NEEDLES OF YOUNG NORWAY SPRUCE (PICEA-ABIES L, KARST)

Drought stress has been shown to decrease O-3-uptake and is thought to mitigate O-3 stress in trees. To test this hypothesis we investigated the effects of ozone fumigation (100 nL/L, 17 weeks) singly and in co mbination with mild drought stress on guaiacol peroxidase (POD) activi ty (EC 1.11.1.7) and lipid peroxidation in Norway spruce needles (Pice a abies L.). After 10 weeks of fumigation a subset of the trees was su bjected to mild drought. Activity of apoplastic guaiacol peroxidase wa s decreased by ozone in needles of well-watered trees. Mild drought ca used a reduction in cumulative ozone-uptake by about 17% as compared t o well-watered trees. In spite of this reduction in ozone-uptake, acti vity of apoplastic guaiacol peroxidase was also low in drought-stresse d ozone-fumigated trees. Ozone exposure caused a slight increase of to tal guaiacol peroxidase activity whereas mild drought led to a decreas e that was more pronounced in combination with ozone. We found enhance d contents of malondialdehyde, an indicator of lipid peroxidation, in drought subjected trees but not as a consequence of ozone exposure.