THE ACTION OF PENETRATING RADIATIONS ON YEAST CELLS

Abstract

Studies of survival of haploid and diploid yeast cells after single exposure to various penetrating radiation and particles led to the recogition of recessive and dominant lethal damage as operative in radiation-caused inhibition of cell division and to the migration model of radiation effects. A single penetrating charged particle (electron, proton, alpha particle, or carbon ion) is capable of producing with types of injury, leading to death in haploid cclls and to death or impaired cell division in diploids. However, the biological site of damage is frequently not the actual site of primary ionization or excitation, but appears to be located at various distances from the track. Migration of the energy appears to be due to diffusion of chemical intermediates or to intramolecular migration of excitation energy. Heavily ionizing particles appear to be capable of producing greater injury farther from the ionizing tracks. In haploid cells lethal damage appears to occur so quickly that so far no postirradiation modifying factors have been demonstrated. In diploid cells, postirradiation factors do influence survival. Sublethal doses of radiation modify these cells for several generations and cause several demonstrable forms of effects. Among these are muta- tions, reduction of growth and cell-division rate, respiratorymore » deficiencies, production of novisble progeny, incressed sensitivity to re-irradiation, and recovery. Whereas progeny of a single irradiated cell are usually impaired in their growth rate and metabolic efficiency, the mutationlike recovery process results in rapidly dividing cells again. This entire phenomenon resembles the time development of radiation- induced carciongenesis in animals, and the underlying factors in the irradiated somatic cells of diploid animal tissue may be very similar. A number of experiments werc carried out studying the effect of continuous x-irradiation on a population of yeast cells in steady-state proliferation in a chemostat. As much as 3000 r delivered in a generation time was well tolerated by the population, which is a few generation times, reached anothcr steady-state, characterized by an increased period required for cell division. (auth)« less