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 combination with mild drought stress on guaiacol peroxidase (POD) activity (EC 1.11.1.7) and lipid peroxidation in Norway spruce needles (Picea abies L.). After 10 weeks of fumigation a subset of the trees was subjected to mild drought. Activity of apoplastic guaiacol peroxidase was decreased by ozone in needles of well-watered trees. Mild drought caused a reduction in cumulative ozone-uptake by about 17% as compared to well-watered trees. In spite of this reduction in ozone-uptake, activity of apoplastic guaiacol peroxidase was also low in drought-stressed ozone-fumigated trees. Ozone exposure caused a slight increase of total guaiacol peroxidase activity whereas mild drought led to a decrease that was more pronounced in combination with ozone. We found enhanced contents of malondialdehyde, an indicator of lipid peroxidation, in drought subjected trees but not as a consequence of ozone exposure.