Dependence of radiation sensitivity on oxygen tension in oedogonium. II. Effect of temperature and LET

The value of K (the O 2 concentration at which one-half of the oxygen-dependent radiation sensitivity is expressed) for two radiations of different LET was investigated in vegetative cells of the alga Oedogonium cardiacum . Oxygen concentration in the water surrounding the cells was controlled by gas bubbling before and during irradiation. From D 0 values of survival curves, K for 300 kVp X-rays was estimated to be 17·6 ± 2·0 μM l −1 . From survival values in air, N 2 and 0·87% O 2 , K for 14 MeV neutrons was estimated to be 8·7 ± 3·8 μM l −1 . At the same oxygen concentration the cells were more sensitive to X-rays at 0–1 °C than at room temperature by about 12 per cent. The change was the same in hypoxic and aerated conditions so that the oxygen enhancement ratio of 2·9 remained the same. The relation between OER and dissolved oxygen concentration was independent of the temperature.