AN ANALYSIS OF THE REJOINING OF X-RAY-INDUCED BROKEN ENDS OF CHROMOSOMES IN THE ROOT TIPS OF ALLIUM CEPA

Abstract

Experiments were performed with the roots of Allium cepa seedlings in order to analyze the rejoining behavior of x-ray-induced broken ends of chromosomes, and to test several hypotheses relating the results of such studies to the nature of chromosome organization. Studies with fractionstcd doses have shown that two classes of breaks, as judged by their average time of restitution, are induced by x-rays--those that undengo relatively rapid restitution within 15 mlnutes, and those that remain open for a relatively long period of time, e.g., four hours. In an effort to distinguish the two classes of breaks on a qualitative basis, experiments utliizing carbon monoxide treatments were performed. Carbon monoxide was found to produce a lightreversible inhibition of the restitution of both types of breaks. The results of these studies indicate that the two classes of breaks cannot be distinguished on this basis. The possibility that iron provides an ionic linkage in the chromosome is discussed. (auth)