Modification of the X-Ray and Ultraviolet Induced Mutation Rate in Aspergillus Terreus by Pretreatment with near Infrared Radiation.

HE modification of a mutation rate induced by X-radiation has been T effected only in Drosophila where the use of low temperatures has been instrumental in significantly raising the rate of recessive lethals (MEDVEDEV 1935; KING 1947), a finding which, however, does not have the support of all investigators in this field (see KING 1947). Should the data of KING and others be further substantiated by additional experimental proof, i t becomes increasingly evident that a close parallelism exists between mutation rate and chromosome breakage on one hand and recombination on the other, since data available from several sources (PAPALASHTVILI 1935; MICKEY 1939; SAX and ENZMANN 1939; HERSKOWITZ 1946) give convincing evidence that low temperatures raise the rate of X-ray-induced chromosomal aberrations. This parallelism may be more apparent than real, however, for the exact relationship between gene and chromosome change still remains somewhat of an enigma insofar as radiation studies are concerned (MULLER 1941). The fact that treatment of the chromosomes of Drosophila and Tradescantia with near infrared radiation prior to X-radiation markedly increases the rate of detectable aberrations (KAUFMANN, HOLLAENDEK and GAY 1946; SWANSON and HOLLAENDER 1946 a, b) suggests that this type of near infrared radiation, which alone is without detectable biological activity when chromosome aberrations and gene mutations are used as criteria of effect, may, in combination with X-radiation, modify the mutation rate. The first report of an attempt of this kind was made by KAUFMANN and GAY (1946), who found that infrared treatment of the X-chromosome of Drosophila was ineffective in influencing those types of induced changes wh&h characterize recessive lethals. It was thought, however, that a study of this sort could profitably be made on the induced mutation rate in the fungi, and it is the purpose of this paper to present the data so obtained. In addition, comparative data on the effect of infrared on the modification of the ultraviolet-induced mutation rate are included, providing information which further emphasizes the differences exhibited by these two mutagenic agents.