Interactive effects of ozone and drought stress on pigments and activities of antioxidative enzymes in Pinus halepensis

The aim of this study was to investigate the interactive effects of ozone (O-3) and drought on pigments and antioxidant enzymes of Aleppo pine (Pinus halepensis). Two-year-old seedlings were exposed in open-top chambers to charcoal-filtered air or non-filtered air plus an additional 40 nL L-1 of ozone. After 20 months Of O-3 exposure, a subset of plants was subjected to drought stress by withholding water supply for 11 d. Ozone induced higher guaiacol peroxidase, catalase and KCN-resistant superoxide dismutase (SOD) activities in young needles, while drought stress increased glutathione reductase and CuZnSOD. One-year-old needles showed lower capacity to activate these enzymes in response to stress. Both ozone and drought activated the xanthophyll cycle pool and reduced chlorophyll contents in both current and 1-year-old needles. The combined effects of ozone and drought decreased antioxidant enzyme activities and the capacity of recovering after rewatering. Similarly, interactive effects Of O-3 and drought reduced xanthophyll-mediated photoprotection capacity in 1-year-oId needles but induced a higher conversion of the cycle in current-year needles. These results showed that ozone modified the Aleppo pine response to drought stress, suggesting that this pollutant might be reducing the ability of this species to withstand other environmental stresses.