EFFECT OF X-RADIATION ON THE DESOXYRIBONUCLEIC ACID AND ON THE SIZE OF GRASSHOPPER EMBRYONIC NUCLEI

¹ Biology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee

1. Cytological and cytochemical studies were made on embryonic nuclei of the grasshopper. Chortophaga viridifasciata, after x-ray doses of 4000, 10,000, and 12.500 r. The changes induced were photometrically measured by using (1) the Feulgen reaction to determine relative changes in the DNA desoxypentose, and (2) the methyl green stain to indicate the degree of polymerization of the nucleic acid.

2. X-radiation was found to cause swelling of the nuclei. When correction was made for this, the Feulgen-stained nuclei showed no significant loss of DNA after irradiation, but the nuclei stained with methyl green disclosed a highly significant loss of stainability. This is interpreted to indicate that x-rays do not destroy the DNA but induce depolymerization of the nucleic acid.

3. This study has shown that it is not safe to make quantitative estimates of DNA (stained by Feulgen or methyl green) from microscopic observations and photographs. The visually apparent loss of Feulgen-stainability after irradiation is probably not due to a decrease in the DNA desoxypentose but rather to the increased dispersion of the DNA in nuclei that have undergone x-ray-induced enlargement.

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