Antioxidants in sun and shade leaves of sour orange trees (Citrus aurantium) after long-term acclimation to elevated CO2

Antioxidative systems and the contents of pigments, malondialdehyde, soluble protein, and carbohydrate were investigated in sun- and shade-acclimated leaves of sour orange (Citrus aurantium) trees that had been grown for 7.5 years under ambient and elevated (+300 μmol mol -1 ) atmospheric CO 2 concentrations. Sun-acclimated leaves contained higher ascorbate, glutathione and soluble carbohydrate contents and higher catalase activities than shade-acclimated leaves. The activities of superoxide dismutases, which belonged to the family of Cu/Zn-isozymes, were similar in sun-and shade-acclimated leaves and decreased in response to enhanced CO 2 . In shade-acclimated leaves, none of the other parameters studied was affected by elevated CO 2 . In sun-acclimated leaves elevated CO 2 caused increases in carbohydrate and ascorbate contents. There was no evidence for enhanced lipid peroxidation as assessed from the determination of the malondialdehyde contents under either conditions.