Ozone-Induced Changes in Antioxidant Systems of Ginkgo Biloba in Relation to the Developmental Stage of the Leaves

Ozone (O₃) pollution has adverse effects on the trees grown in urban area. Using open top chambers, responses of antioxidant systems were detected in Ginkgo biloba leaves at different developmental stages after a long term O₃ exposure (O₃ concentration ≈ 80 nmol mol^-1). As leaf size is closely related to the developmental stage, leaves with different sizes were chosen to indicate the various developmental stages. The results suggested that activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT) were induced to a higher level in younger leaves with 50% expansion size under elevated O₃ exposure, whereas O₃-induced decrease in APX and SOD activities was found in the 80% and 100% expanded ones. Dehydroascorbate reductase (DHAR) activity and ascorbate (Asc) content were not affected by high O₃ in 50% expanded leaves, but the O₃-induced decrease in them occurred in the 80% and 100% expanded ones. Malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) contents increased significantly in the 80% and 100% expanded leaves at elevated O₃. However, O₃-induced increase in MDA and H₂O₂ contents did not reach the significant level in the 50% expanded leaves, indicating the higher resistance to O₃ in the younger leaves. The positive responses of antioxidant systems could be responsible for the higher resistance to O₃ in the younger leaves.