Antioxidative defense and photoprotection in Pinus halepensis induced by Mediterranean conditions and ozone exposure

Pigment levels and antioxidative stress-related metabolites were determined over a period of two years in Pinus halepensis to characterize the respons e of some plant protective processes to both environmental stresses and O-3 exposure. Two-year-old-Aleppo pine seedlings were grown in open-top chambe rs under optimal nutrient and water conditions and exposed to different O-3 levels: charcoal filtered air, non-filtered air and nonfiltered air plus 4 0 ppb O-3 10 h/day. In summer an activation of photoprotective systems was observed since a decrease in chlorophyll levels, an increase in the caroten oid/chlorophyll ratio and SOD activation were recorded. Interestingly, the SOD activity in Pinus halepensis was highly related to low-molecular weight compounds and this relationship increased with needle age. Ozone exposure induced alterations in the activity of some antioxidant enzymes along with reductions in pigment concentrations and an activation of the xanthophyll c ycle.