Ozone effects on the metabolism and the antioxidant system in poplar leaves at different stages of development

During Leaf Development Significant Metabolic Changes Occur. Leaf Development In Its First Stages Has Been Associated With An Increase In Photosynthetic Activity And In The Oxidative Damage, Which May Be Exacerbated By Exposure To Ozone. In This Work, Poplar Saplings Were Subjected To A High But Realistic Ozone Level (100 Ppb) For 10 Days. H2O2 And Lipid Peroxidation Levels, Photosynthesis And Photosynthetic Metabolites (Glucose, Pyruvate), Antioxidants (Phenolics, Ascorbic Acid) And Some Antioxidant Enzyme Activities Were Measured In Control And Ozone-Treated Poplar Leaves At Two Stages Of Development. Young Control Leaves Showed A Lower Photosynthesis And A Higher Concentration Of All Studied Metabolites Than Mature Control Leaves. The Latter Finding Supports The Theory That Developing, More Vulnerable, Leaves Need More Chemical Defence. However, Developing Ozone-Treated Leaves Presented Higher Photosynthesis And Lower Levels Of Metabolites Than Developing Control Leaves. This May Indicate A Faster Development Of Ozone Treated Leaves. In Fully Expanded (Mature) Leaves, As A Response To Ozone, The Activities Of Antioxidant Enzymes (Ascorbate Peroxidase And Catalase), And The Concentration Of Phenolics Increased, Whereas Ascorbate Concentration Did Not Change. This May Indicate That Both Induction Of Phenolics And The Action Of The Ascorbate-Glutathione Cycle Play A Significant Role In Protecting Fully Developed Poplar Leaves Against Ozone. In The Last Case, The Higher Activity Seems To Be Controlled By The Enzyme Activities And Not By The Concentration Of Ascorbic Acid.