Chemical Protection against X-Ray Damage to Chromosomes.

HE writer (RILEY 1955) has shown that 2 X and 2 X lop4 M sodium T hydrosulfite and 2 X 2 X lop3, and sometimes 2 X lop4 M 2,3-dimercaptopropanol (BAL) will reduce significantly the number of chromosome interchanges and deletions induced by gamma radiation in root tips from germinating onion bulbs if the roots are in the solutions from 30 minutes before until ten minutes after irradiation. A similar effect was found even when the roots were removed from the solutions during the short period of irradiation, probably because they were covered with and apparently saturated with the solutions during that time. When the frequency of chromatin bridges a t anaphase was used as a measure of radiation damage to root-tip chromosomes from young onion seedlings, significant protection was conferred by 4 X lW3 and 4 X lW4 M sodium hydrosulfite and by 4 X and 4 x lop3 M BAL when given before, during, and after irradiation but not by lower concentrations of the same compounds. Sodium pyrosulfate in concentrations of 4 X le2, 4 X lW3, and 4 X M showed great protection, but 4 X 1W2, 4 X lW3, and 4 X le4 M sodium peroxidisulfate resulted in a reduction in bridges that was not statistically significant. A 2.8 x 10-1 M concentration of glucose brought about no reduction in bridge frequency and 1.7 M ethanol showed some reduction although the reduction was not significant. In the present paper these and other chemical compounds are discussed as protective agents against chromosome damage by X-rays.