Inaccuracy of anaphase bridges as a measure of radiation-induced nuclear damage.

Abstract

ONE of the most significant contributions that led to the development of the target theory in regard to chromosome aberrations was Sax's observation1 that X-ray-induced dicentrics and rings, which require two breaks or hits, increase as the square of the dose. There have been numerous reports in the literature, however, of a linear dose curve resulting from the scoring of anaphase bridges that ostensibly come from the dicentrics and rings. Even Sax himself has reported in a paper by Sax and Brumfield2 such a linear one-hit curve in the seed of Vicia faba. Later, Wolff3 found that if the metaphase configurations in Vicia were scored, the theoretically important parabolic two-hit curve was obtained. The differences in these two curves were attributed to many diverse phenomena. Wolff thought that the difference between his curves and those of Sax and Brumfield might be due to the fact that they may have scored single bridges resulting from one-hit isochromatid breaks, rather than the double bridges associated with dicentrics and rings. Caldecott4,5, however, in a series of papers in which he obtained the linear curve for anaphase bridges in barley, observed that the bridges were all double, and postulated that the apparent contradiction between Sax's and Wolff's two-hit curves on one hand, and Caldecott's and Sax and Brumfield's one-hit curves on the other, might be due to differences in hydration of the material5. Since the two-hit curve is of very great importance for the theory of the production of chromosome aberrations, it is important that the discrepancy in the two types of curves be studied.