The Effect of Cold Treatment on the Desoxyribonucleic Acid (DNA) Content in Cells of Selected Plants and Animals

Abstract

Three plant species and one animal species have been subjected to cold treatment in order to determine whether or not the DNA content of the cells shows a reduction. The following conclusions have been drawn from this study:
1. A decrease in the amount of DNA results from cold treatment in Trillium erectum and Trillium sessile which is observable both by microscopic observations and by spectrophotometric measurements. These two species show no noticeable decrease in mitotic processes when cold treated. Tradescantia edwardsiana, which has supernumerary chromosomes, shows a slight increase in DNA which is attributed to the suppression of mitotic activity. Chortophaga viridifasciata does not show any significant change in meiosis subsequent to pachytene, and there is a systematic halving of the quantity of DNA corresponding to the divisions in meiosis.
2. There are at least two types of DNA present in Trillium erectum and Trillium sessile, a stable type associated with gene-bearing regions and a more labile type found in heterochromatic regions. The decrease of DNA caused by cold treatment appears to be due to a deficiency of this labile fraction of DNA.
3. Cold treatment of chromosomes results in manifestations remarkably similar to effects from other physical and chemical agents, such as 5-aminouracil and an ultraviolet microbeam.
4. The changes in quantity of DNA due to cold treatment occur only in selected plants having large heterochromatic regions and ones which are able to continue mitotic processes despite severe alteration of the environment. For these reasons, it is believed that reduction of DNA content as shown in this study does not invalidate the usefulness of the concept of constancy of DNA as currently advocated by Swift and others.