The nucleic acid content of cells in the meristematic elongating and fully elongated segments of roots of Vicia faba

Abstract

By combined cell counting and biochemical assay, the mean DNA and RNA content of the cells in the root tip of Vicia faba seedlings has been measured. The values for segments 0–2, 2–4, 4–8 and 12–20 mm behind the root cap were found to be, for DNAP, 3.5 7 ± 0.2 0, 4.00 ± 0.20, 4.5 5 ± 0.3 7 and 4.7 0 ± 0.3 2, 10 −12 grams, and for RNAP, 14.2 ± 0.54, 16.1 ± 0.63, 18.0 ± 0.99, and 16.5 ± 0.86, 10 −12 grams. The approximate amounts of phosphorus per cell in other forms were also estimated. The nucleic acid determinations show that the mean DNA content per cell steadily increases with distance from the root apex, being 30 per cent greater in the proximal segment, which is composed mainly of fully differentiated cells, than in the terminal segment, which is entirely meristematic. Thus, if the average meristematic cell at the commencement of interphase is assumed to have a diploid content of DNA, then the mean DNA content of the differentiated cells is approximately tetraploid.