The Response of Diploid Yeast to Radiations at Different LET: I. Potentially Lethal and Lethal Damage to Reproductive Capacity

Stationary populations of diploid yeast (Saccharomyces cerevisiae, wild type, strain No. 211) were irradiated with sparsely and densely ionizing radiations at high and in part at low dose rates. Mean LET values ranged from 0.1 to 600 keV/m. The reproductive capacity of the cells was measured by macrocolony counting. After irradiation at high dose rates, agar-holding reactivation was allowed for 48 hr. Dose-effect curves showed a change from sigmoidal to exponential form with increasing LET and a maximum of the slope of the exponential part at about 70 keV/m. If the radiation response at higher doses is separated into contributions of potentially lethal and of lethal damage, one finds different dependence on the mean LET. The observed lethal damage production is discussed in terms of single-hit events expected from theoretical considerations.