Effect of Ploidy on the Response of V79 Cells to Ionizing Radiation

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Abstract
The responses of diploid, tetraploid and near-hexaploid V79 cells to X-irradiation or DNA-associated 125I-decay were compared. When cell killing, following X-irradiation, was plotted against the induced level of DNA double-strand breakage (dsb) per unit length of DNA, there was no significant difference between the relationships for each cell line. This suggested that the number of X-ray-induced DNA dsb per cell required to produce a lethal lesion was proportional to ploidy. Consistent with the X-ray results, tetraploid cells required 121 ± 4 and diploid cells 60 ± 1 125I-decays to produce a lethal lesion. However, the hexaploid cells deviated from this relationship and required 137 ± 5 decays. The relationship between relative elution and 125I decays/cell reflected cellular DNA content. It is concluded that current models of radiation action are unable to explain these findings satisfactorily.