Effect of the exogenous anthocyanin extract on key metabolic pathways and antioxidant status of Brazilian elodea (Egeria densa (Planch.) Casp.) exposed to cadmium and manganese

Present study deals with the effect of 24 h pre-incubation with exogenous anthocyanins (ANTH), extracted from red cabbage leaves, on key metabolic processes (photosynthesis and respiration) and pro-/antioxidant balance in the aquatic macrophyte Egeria densa (Planch.) Casp., Hydrocharitaceae family, treated with Cd and Mn (in sulfate form) at a concentration of 100 μmol. After five days of metal treatments, Cd was accumulated and the damage caused to metabolic processes was stronger than Mn. In Cd-treated leaves, the protein level, chlorophyll concentration and maximal photochemical efficiency of PS II decreased twofold, and net-photosynthesis was significantly inhibited, whereas lipid peroxidation and H₂O₂ production increased. In turn, protective responses developed, including an increase in the total soluble thiols, alternative respiratory pathway capacity and the activity of superoxide dismutase and peroxidases. Pre-incubation in the ANTH-enriched extract caused an increase in foliar ANTH content, enhanced Cd and reduced Mn uptake into the tissue. A decrease in the level of oxidative reactions, an increase in the protein and chlorophyll concentration compared to the control values and a partial improvement of the photosynthetic parameters confirmed the ability of ANTH to reduce Cd-induced damage effects and to mitigate ROS-driven stress reactions. Stimulation of catalase and ascorbate peroxidase activity, an alternative respiration capacity and non-enzymatic antioxidant (carotenoids, ascorbate and proline) synthesis by ANTH were also revealed. These data suggest that ANTH-enriched extract from red cabbage leaves has a protective action against metal toxicity in Egeria plants.