THE FREQUENCY OF X-RAY INDUCED CHROMOSOME ABERRATIONS IN TRADESCANTIA AS MODIFIED BY NEAR INFRARED RADIATION

Abstract

REVIOUS investigations have shown that infrared radiation is effective P in increasing the number of chromosomal aberrations resulting from Xradiation When used alone, however, infrared radiation has no visible effect upon the chromosome. During recent years, these radiations have been used in combination with mutagenic agents to investigate numerous problems. Although increases in chromatid aberrations have been secured in Tradescantia, the effect of infrared radiation upon the induction of chromosome aberrations has not been tested. It was felt that an extension of the investigation to cover chromosome aberrations might lead to a solution of certain problems which had arisen in the earlier studies. On the one hand, two hypotheses have been advanced to explain the mechanism of action of infrared radiation in producing its effect. One states that infrared radiation affects only the process of recombination, favoring recombinations over restitution (KAUFMANN, HOLLAENDER and GAY 1946). The other postulates that the effect is to increase the total number of primary breaks (SWANSON and HOL-LAENDER 1946). As the recombination process takes place during and after X-radiation, it seemed that investigations of the effects of posttreatments with infrared radiations should help to discriminate between these two hypotheses. Tradescantia possesses certain advantages for such an investigation, since the period of recombination following X-radiation has been shown to be very short Utilization of chromosome rather fhan chromatid aberrations permits an extension of the period of effective posttreatments to at least 96 hours after X-radiation. If the effect of the infrared were upon the recombination process alone, posttreatment effects would be limited to the time interval established for the process in Tradescantia, that is, during the first hour after X-radiation. This did not prove to be the case, as the data presented in this paper show.