Nucleic acid content and concentration in root cells of higher plants

Abstract

The absolute amounts and concentrations of RNA and DNA per cell in root apices (0–2 mm) of eleven species of higher plants were measured. There was a 57-fold variation between species in the average amount of DNA per cell and an 80-fold variation in the average amount of DNA per chromosome. There was only a sevenfold variation in the average amount of RNA per cell. There was a twofold variation in the concentration of RNA per cell and a sixfold variation in the concentration of DNA per nucleus. As the RNA content per cell increased, the RNA concentration decreased, but as the DNA content per nucleus increased, the DNA concentration also increased. The largest cells and nuclei, the highest amounts of RNA and DNA per cell and the highest concentrations of DNA in the nuclei were found in the monocotyledons studied. The highest concentrations of RNA per cell, however, were found in the dicotyledons. Measurements were also made on segments 2–4, 4–6 and 6–8 mm from the root apices of six of the species. The progress of cell expansion from the first to the fourth segments was accompanied, in five species, by increases in the average amounts of both RNA and DNA per cell. In the sixth species, the amount of RNA per cell increased but the amount of DNA decreased slightly. The increase in the amount of RNA per cell, which varied from about 50 to 70 per cent, exceeded the increase in the amount of DNA per cell in several species. The concentration of RNA per cell fell markedly during cess growth in all species. The concentration of DNA, however, remained constant in most of the nuclei, but fell in a few nuclei situated in the vascular and outer cortical tissues.