Hormesis effect display in yeast cells exposed to ionizing radiation

A comparative study of quantitative regularities of haploid and diploid yeast cell dying in unnu-trient media was carried out for various strains exposed to ionizing radiation. Cell dying was observed in control and cells treated to chronical (γ-rays of 137Cs) and acute (γ-rays of 60Co) irradiation. It was established that after chronical (for a month at 30 0C) treatment of ionizing radiation at the dose rate range 3-10-2 - 102 of the natural radiation background resulted in the reduction of the cell dying velocity. In these experiments the reverse dose rate effect was obtained - the lower doses and dose rates of ionizing radiation were more effective in comparison with the higher doses and dose rates. The single acute treatment at room temperature resulted in the reduction of dying of cells surviving after irradiation. The cell dying has taken place at 37 и 40 0C. This process was registered not only at low doses decreasing cell survival to 70-90 % but also at high doses when cell survival was only a few percents. The radiation hormesis effect was shown to be slightly expressed for haploid yeast cells. The results obtained in this paper are interpreted within the traditional hypothesis about the role of reparation systems in hormesis effects.