Effects Of Elevated Ozone On Active Oxygen Species And Anti-oxidative System In Ginkgo Biloba L. And Pinus Tabulaeformis Carr

The Ginkgo biloba L. and Pinus tabulaeformis Carr.trees are exposed in the open-topchambers to two levels of ozone concentration (ambient, approximately 45nmol/mol andelevated ozone, 80±8 nmol·mol^-1)in order to study the effect of elevated ozone on activeoxygen species, lipid peroxidation and antioxidative systerm in Pinus tabulaeformis Carr. andGinkgo biloba L. leaves.The membrane permeability and content of MDA are increased after 30 days exposure tothe elevated ozone. The membrane permeability and MDA content as an index of lipidperoxidation is increased significantly with the prolonged exposure to the elevated ozone. TheO₂^- generating rate and the content of H₂O₂ are aslo induced accumulatively by the elevatedozone, and the extent is increased with the prolonged treatment days. It shows that the effectsof ozone on active oxygen species in two trees were accumulatived.The activities of SOD, APX, MDAR and GR are enhanced in the first stage of thetreatment days, and then descresed significantly compared to the control.However, thechanges in DHAR in two trees are differently from the others antidative enzymes to theexposure of ozone. The activities of DHAR in the two trees are decreaced by the elevatedozone in the first stage of treatment days; however, it is induced with the prolonged treatmentdays. The changes of antidative enzymes in Ginkgo biloba L. are much more significant thanthe enzymes in Pinus tabulaeformis Carr.The ascorbate contents in Pinus tabulaeformis Carr.and Ginkgo biloba L. leaves are alsodescresed by the elevated ozone. The ascorbate content in Ginkgo biloba L. leaves isdescresed significantly in the first stage of the treatment days, neither was the Pinustabulaeformis Carr.However, the ascorbate content in Pinus tabulaeformis Carr.is descresedsignificantly in the middle and last the stage of the treatment days. The result shows that theresistence of Ginkgo biloba L. was more subtle than Pinus tabulaeformis Carr.to elevatedozone.The net photosynthetic rates both of Pinus tabulaeformis Carr.and Ginkgo biloba L.leaves also decrease to the exposure of elevated ozone. However, the changes in chlorophyllcontent both of the trees are not stable and significant, especially in the Ginkgo biloba L.leaves. This may be explained by the significant increase in carotenoids content in Ginkgobiloba L.leaves which protected chlorophyll from photooxidation and lipid peroxidation. Butthe carotenoids content in Pinus tabulaeformis Carr.leaves is not significantly in the firststage of the treatment days, and the extent increases with the prolonged treatment days.The activities of antidative enzymes and antioxidant could not resisit the injury of thehingher level of active oxygen species, and can not scavenge the enhanced active oxygenspecies induced by the exposure of elevated ozone The decreases in photosynthesis areexplained by the significant increase in membrane permeability and content of MDA which isan important product of lipid peroxidation that occurred on cellular membrane systemsincluding antioxidative systerm.