Hyperaccumulation of cesium by duckweed Lemna minor

Cesium-137 is one of the most common radioactive isotopes that are released into the environment during nuclear accidents. Because of the relatively long half-life time, cesium-137 is still present in significant amounts in fresh waters and soils in the areas surrounding nuclear accident sites that occurred in the second half of the 20th and early 21st centuries. Many freshwater organisms have the ability to absorb cesium from the environment. It has been shown in experiments with the Lemna minor plants grown in the wild that this duckweed is one of the most efficient cesium accumulators among higher aquatic plants. In order to study duckweed accumulation capacities under the laboratory conditions, we grew aseptic L. minor plants on various cesium-containing culture media. The conditions for laboratory aseptic cultivation of two L. minor strains of different origin (Clone ID - 0008-14-LUG (Lm-14) and RDSC Clone 5500 (Lm-55)) were optimized. The accumulation of cesium ions by L. minor plants in a wide range of Cs+ concentrations in culture media in the presence of K+ ions in both low (mM) and high (mM) concentrations was studied. We also evaluated the viability of duckweed plants and measured the growth parameters of the plants under these growth conditions. The coefficients of Cs+ accumulation were determined and the effect of potassium ions on the accumulation of Cs+ was investigated. In aseptic conditions at micromolar K+ concentrations, the accumulation coefficients of Cs+ were found to be from 200 to 400. We also have shown that L. minor is able to accumulate cesium ions to the hyperaccumulation levels. These findings indicate a potential use of L. minor plants for remediation of water bodies contaminated with radioactive cesium. Our data on Cs+ accumulation in the presence of K+ both in low and high concentrations in the culture media also show that there is a competition between Cs+ and K+ ions for K+ -transporting proteins. We suggested that both the high affinity and the low affinity K+ transport systems may participate in the Cs+ absorption by duckweed plants, depending on the K+ and Cs+ concentrations in the medium, in particular a high affinity transporter of the HAK family or a K+-channel of the AKT shaker family.