The mechanism of the effect of postirradiation centrifugation on the yield and the kinetics of radiation-induced chromosome aberrations in barley.

CENTRIFUGATION during or after a dose of radiation has been found to increase the yield of chromosome aberrations in Tradescantia microspores and Vicia faba root meristems (SAX 1943; WOLFF and VON BORSTEL 1954; ANDERSON 1955). These observations suggested that altered positional arrangement of chromosome strands in the interphase nuclei, arising from centrifugation, resulted in reduced restitution of the broken ends, and consequently in an increased yield of chromosome aberrations. It was further observed, in experiments where postirradiation centrifugation was applied to the cells exposed to different gaseous conditions prior to and during irradiation, that the enhancement effect was lackirig in cells subjected to anoxia (WOLFF and VON BORSTEL 1954; ANDERSON 1955). On the basis of these observations, it was argued that a part of the centrifugation effect, particularly the centriiugation enhancement observed during irradiation, could be the result of an oxygen effect arising from reduced respiration during centrifugation (EVANS 1962). An examination of the centrifugation effect separated from the effects of other postirradiation factors was not possible in these experiments. In the present paper, data are presented which show that (1) the centrifugation effect is highly significant even after the effect of other controllable postirradiation variables has been considered, (2) the centrifugation effect results from an increase in the number of sites of exchanges, and (3 ) the centrifugation effect is dose-dependent and the kinetics of chromosome aberrations are altered.