Influence of Oxygen upon Genetic and Nongenetic Effects of Ionizing Radiation on Paramecium aurelia.

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Abstract
The nongenetic effects of ionizing radiation upon Paramecium aurelia when many bacteria are present during irradiation, are not influenced or perhaps are slightly increased by hypoxia. However, when few bacteria are present, these effects are decreased by hypoxia. The latter finding is in accord with the previous evidence that much of the nongenetic damage produced when few bacteria are present is due to H2O2 formed outside the cell. The former finding suggests that H2O2 formed inside the cell is not of importance in producing nongenetic damage. On the other hand, genetic damage is consistently less under hypoxia. Previous evidence has shown that this kind of damage is not produced by H2O2 formed outside the cell. However, it seems quite possible that H2O2 or HO2 produced locally within the nucleus is of importance in producing this kind of damage; but the evidence from Paramecium does not exclude other interpretations.