Sensitivity of Interphase Cells to Chromosome Breakage by X-rays

Abstract

SEVERAL previous studies have dealt with the sensitivity of interphase cells to chromosome breakage by X-rays. In the root tips of beans (Vicia faba) Revell¹ observed that the sensitivity reaches its maximum about 8 hr. prior to mitosis. According to Howard and Pelc² this time lies in the post-DNA-synthetic period (G₂). The results obtained by Sparrow et al.³ in Trillium microspores are also similar to those of Revell. In a recent investigation of the survival of HeLa cells Terasima and Tolmach⁴ have found that the irradiation of interphase cells, which are presumably in the process of synthesis of DKA (S), reduces their capacity to form colonies more markedly than when they are irradiated at other stages of interphase. In the present work, using tritiated-thymidine to identify directly DJMA-synthesizing cells, it is shown that these cells, which are in the S-phase at the time of irradiation, are more sensitive to chromosome breakage than cells at other stages of interphase (G₁ and G₂).