Interactive effects of ozone and drought stress on pigments and activitiesof 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 ch arcoal-filtered air or non-filtered air plus an additional 40 nL L-1 of ozo ne. After 20 months Of O-3 exposure, a subset of plants was subjected to dr ought stress by withholding water supply for 11 d. Ozone induced higher gua iacol peroxidase, catalase and KCN-resistant superoxide dismutase (SOD) act ivities in young needles, while drought stress increased glutathione reduct ase and CuZnSOD. One-year-old needles showed lower capacity to activate the se enzymes in response to stress. Both ozone and drought activated the xant hophyll cycle pool and reduced chlorophyll contents in both current and 1-y ear-old needles. The combined effects of ozone and drought decreased antiox idant enzyme activities and the capacity of recovering after rewatering. Si milarly, interactive effects Of O-3 and drought reduced xanthophyll-mediate d photoprotection capacity in 1-year-oId needles but induced a higher conve rsion 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.