Responses of yeast cells to heat applied alone or combined with gamma-rays

Experiments were carried out to determine the effects of hyperthermia alone or combined with gamma-rays on the survival of yeast cells of different species. Arrhenius plots for the heat inactivation of yeast cells show inflection points. This suggests that hyperthermic killing above or below these temperatures is mediated by different mechanisms. The synergism between hyperthermia and ionizing radiation was almost linearly dependent on temperature as shown by Arrhenius plots for the combined action of both modalities. The data obtained may imply that different processes are involved in heat inactivation and thermal enhancement of yeast cell radiosensitivity.