In the present study, we investigated the accumulation of ¹³⁷Cs and ⁹⁰Sr in compartments of the Nitellopsis obtusa cells. The effect of Sr²⁺, Cs⁺ and Ca²⁺, K⁺, which are chemical analogues of ⁹⁰Sr and ¹³⁷Cs, to the bioelectric parameters of these algae were studied simultaneously. The aim of this work was studying the penetration of ¹³⁷Cs and ⁹⁰Sr through regulating membrane barriers in the cells of starry stonewort (Nitellopsis obtusa). ¹³⁷Cs and ⁹⁰Sr are accumulated mainly in the cell membrane (75% to 92%) of these algae. The cell membrane as a cation exchanger regulates ion flow through the first cells diffusion barrier – its thick outer cytomembrane (the complex consisting of the cell wall and plasmalemma). Significantly, smaller amounts of ¹³⁷Cs and ⁹⁰Sr enter into the cytoplasm than in the cytomembrane, 10-20% and 3-10%, respectively. Analysis of the accumulation levels of ¹³⁷Cs and ⁹⁰Sr in the compartments of the Nitellopsis obtusa cells show their accumulation in the cell membrane as well as their active transport through outer and inner cytoplasmic membranes. Membrane potentials determined mainly by the gradient of the K⁺ ions are doing an important regulatory function in this process. From the obtained data it results that cells of Nitellopsis obtusa algae can be a convenient radioecological model for the study of the accumulation of radionuclides in plants at the cellular level.

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