Phytotoxicity of cesium for duckweed Lemna minor L.

Radiocesium contamination of surface water bodies is one of the most dangerous for biota and humans. The duality of the toxic effects of radionuclides on living organisms is expressed in the combined effect of radiation and a chemical agent in the form of heavy metal ions. The study of the reaction of plants to stable cesium is important for revealing the mechanisms of action of radioactive isotopes, as well as the search for effective phytoremediators of contaminated areas of water bodies. In this work, we studied the phytotoxicity of cesium for a free-floating freshwater plant, duckweed (Lemna minor L.). The laboratory culture was grown on a Steinberg's medium with the addition of 0.17; 0.51; 0.85; 1.19; 1.36; 1.53; 2.55; 3.4 mmol/l cesium. Seven days after the start of the experiment, the specific growth rate, the number of plants with chlorosis and necrosis, and the average surface area of the frond were calculated. Biochemical parameters (sum of chlorophylls (a + b), carotenoids, malondialdehyde) were determined four days after the start of the experiment. Stable cesium in naturally occurring concentrations is non-toxic to duckweed. Cesium in millimolar concentrations had an inhibitory effect on the specific growth rate, led to a reduction in the average area of the fronds, the appearance of plants with chlorosis and necrosis. High concentrations of cesium had pro-oxidant properties, increasing lipid peroxidation of membranes, which was confirmed by an increase in the content of malondialdehyde. Exposure to cesium led to a decrease in the concentration of chlorophylls (a + b) and carotenoids to 20 % of the level of control plants. The results of the study confirmed the possibility of using Lemna minor for phytoremediation of radiocesium contaminated water bodies.