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, s oluble protein, and carbohydrate were investigated in sun- and shade-a cclimated leaves of sour orange (Citrus aurantium) trees that had been grown for 7.5 years under ambient and elevated (+300 mu mol mol(-1)) atmospheric CO2 concentrations. Sun-acclimated leaves contained higher ascorbate, glutathione and soluble carbohydrate contents and higher c atalase activities than shade-acclimated leaves. The activities of sup eroxide dismutases, which belonged to the family of Cu/Zn-isozymes, we re similar in sun- and shade-acclimated leaves and decreased in respon se to enhanced CO2. In shade-acclimated leaves, none of the other para meters studied was affected by elevated CO2. In sun-acclimated leaves elevated CO2 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 condit ions.