Lipid Peroxidation Rates, Hydrogen Peroxide Content, and Superoxide Dismutase Activity in Leaves of a Facultative CAM Plant Hylotelephium Triphyllum (haw.) Holub and a C3 Plant Plantago Media L. under Natural Environmental Conditions

Key indicators of pro-/antioxidant status were studied in leaves of Plantago media L. (C3 species) and Hylotelephium triphyllum (Haw.) Holub (facultative CAM species) grown in the unclosed floodplain meadow biogeocenosis in the middle taiga subzone of the Komi Republic (European Northeast of Russia). During the period of reproductive development, the average content of lipid peroxidation products in leaves of H. triphyllum was 400 nmol/g dry wt, which was 1.2 times higher than in P. media leaves. The content of hydrogen peroxide (Н2О2) in leaves of H. triphyllum reached the level of 90 μmol/g dry wt while it did not exceed 25 μmol/g dry wt in P. media. Activity of superoxide dismutase (SOD) in leaves of H. triphyllum ranged between 50 and 80 unit/mg protein, which was 2–3 times higher than in the leaves of P. media. The treatment of H. triphyllum leaves with an oxidative stress inducer methyl viologen (10 μM) increased SOD activity by 1.6 times but had no significant influence on H2O2 content and the accumulation of lipid peroxidation products. Thus, H. triphyllum leaves were characterized by a higher pro-/antioxidant status than the leaves of a C3 P. media plant grown under identical environmental conditions; this elevated status was due to the operation of CAM photosynthesis in H. triphyllum leaves. The transition of H. triphyllum to CAM photosynthesis during reproductive development is indicated by previously revealed regular diurnal changes in cell sap acidity, malate content, and phosphoenolpyruvate carboxylase activity. The results are consistent with the notion that an increased pro-/antioxidant status is a general feature of CAM plant metabolism, while the consistently high Н2О2 content provides evidence for the involvement of Н2О2 in regulation of crassulacean acid metabolism.