Quantitative relationships between deoxyribonucleic and ribonucleic acid in isolated plant nuclei

Abstract

Nuclei were isolated from the roots of different species of higher plants and the amounts of both deoxyribonucleic acid ( DNA ) and ribonucleic acid ( RNA ) in these nuclei were determined by a modification of the Schmidt-Thannhauser procedure. A new method of isolation was used which involved fixing the roots for a short time in ice-cold 2% (w/v) formaldehyde, and then crushing them in a press. Between 25 and 50% of the nuclei known to be present in the roots could be recovered. It was shown by interferometry, microphotometry and autoradiography, as well as by an examination of all the solutions used, that there was no significant loss of nucleic acids from the nuclei during the isolation procedure. Nuclei from root apices of diploid, tetraploid and hexaploid Allium species, from diploid and tetraploid forms of Tradescantia ohioensis and from Vicia faba , Pisum sativum and Zea mays showed large differences in DNA content. However, these were not accompanied by corresponding differences in RNA content; the DNA ; RNA ratio varied from about unity to more than ten irrespective of the relative amounts of meristematic and differentiating tissue present in the roots. In the nuclei of four of these species, the DNA ; RNA ratio increased as the temperature at which the plants were grown was raised from 4 to 25°C. The results of all these experiments showed the absence of any correlation between the amount of DNA and the total amount of nuclear RNA ; but the possible existence of a correlation between DNA and chromosomal RNA was not excluded.