Levels of primary induced double-strand breaks in DNA of Chlamydomonas reinhardtii (A, C where 1,2 – control; 3, 4 – 0.03 mM; 5, 6 – 0.06 mM; 7, 8 – 0.11 mM; 9, 10 – 0.22 mM; 11, 12 – 0.45 mM) and Saccharomyces cerevisiae (B, D where 1, 2 – control; 3, 4 – 0.5 mM; 5, 6 – 1.7 mM; 7, 8 – 3.7 mM) after the treatment with various PbCl2 concentrations. Values represent the mean fraction of DNA released (FDR). Data are presented as mean ± SEM. All the results are from at least three independent experiments (ns P > 0.05; ** P < 0.01; *** P < 0.001). Where no error bars are evident, they are equal to, or smaller than, the values.