Interaction between Cadmium and Manganese in Aquatic Macrophytes (Illustrated by Elodea Canadensis)

The mutual effect of two heavy metals – toxic (Cd2+) and essential (Mn2+) on the aquatic plant was studied in model systems. Experiments were performed on submerged aquatic macrophyte – Elodea canadensis Michx. Elodea shoots (10–15 cm in length) were incubated for 5 days in a nutrient solution with CdSO4 and MnSO4 at the concentration of 100 μmoles (added separate and combined). The following characteristics were analyzed in Elodea leaves: the accumulation of Cd2+ and Mn2+; the content of photosynthetic pigments and its ratio; the level of chlorophyll fluorescence (quantum efficiency, Fv/Fm). Incubation of Elodea plants with Cd2+ increased its content by more than 1000 times compared to the control. Incubation with Mn2+ increased its content by 10 times. The combined effect of cadmium and manganese reduced Cd2+ accumulation in the Elodea leaves almost in 2 times in comparison with its separate action, while the Mn2+ accumulation was decreased only by 40 %. Under the cadmium action the content of all photosynthetic pigments was decreased, while by the manganese action – only chlorophylls were reduced. It was shown that Mn2+ mitigated Cd2+ toxicity. The content of chlorophyll a, carotenoids and quantum efficiency (Fv/Fm) was decreased to the lesser degree than under the separate cadmium action. Probably this is caused by the inhibition of its uptake in the presence of manganese.