GENETIC-CONTROL OF RBE OF ALPHA-PARTICLES FOR YEAST-CELLS IRRADIATED IN STATIONARY AND EXPONENTIAL PHASE OF GROWTH

Survival curves of S. cerevisiae wild type and rad 50, 51, 52 and 54 m utants in haploid and diploid strains were measured after gamma-ray an d alpha-particle irradiation in stationary and exponential phase of gr owth. The values of RBE of high-LET radiation, defined as the ratio of the mean lethal doses after sparsely and densely ionizing radiations, were determined. A correlation between the RBE of alpha-particles and cell repair capacity was supported for stationary phase cultures. For the first time, it was shown for all strains studied that at exponent ial phase of growth the RBE of ct-particle-induced survival was decrea sed in comparison with that for stationary cells. For most mutant cell s RBE was dose to unity, i.e. cell radiosensitivity was almost identic al for both sparsely and densely ionizing radiation. Possible reasons for the observed radiation responses are discussed.