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

Summary

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.

• DNA double-strand breaks
• X-irradiation
• ¹²⁵I
• ploidy
• nocodazole