Dependence of X-Ray Sensitivity of Yeast on Phase State and Anoxia

Most investigations on the modification of radiation damage in microorganisms have been primarily if not entirely concerned with primary physicochemical processes (i.e., modification of quality and quantity of free radical production), and it has not been necessary to consider the influence of biological factors in explaining the modification of X-ray sensitivity by such treatments as anoxia (1-3), phase state changes (4-6), and addition of various chemicals (7). In this investigation the influence of two modifying factors, anoxia and phase state change (liquid state versus frozen state), used both singly and together, on two closely related strains of haploid yeasts has been studied. If only physical processes concerned with the formation of free radicals are involved, the dose modifying factors2 (DMFs) for these two strains should be identical. Beam has found that the same degree of protection is afforded by anoxic conditions for a haploid yeast and its related diploid and tetraploid strains (2). The two strains of haploid yeast studied here, however, have quite different DMFs for the two modifying agents used, and hence a broader interpretation of the migration model must be invoked.