Autoradiographic Evidence for Incorporation of 2-Aminopurine into DNA and RNA of Plant Cells

Abstract

Root tip cells of Vicia faba, treated with tritiated 2-aminopurine (2AP), were found to be labeled in the nucleus, nucleolus and cytoplasm, thus indicating incorporation into DNA and RNA. In cells fixed immediately after treatment about two-thirds of the label was observed over the nucleus (including nucleolus), after one cell division this distribution was reversed, and after two cell division cycles the grain count was about the same over nucleus and cytoplasm. The reduction and changing distribution of average grain counts through two cell division cycles can be attributed to: 1) distribution of half the labeled DNA and RNA to each daughter cell, 2) shift of labeled RNA from nucleolus to cytoplasm, and 3) metabolic turnover of labeled cytoplasmic RNA.
Characteristics of the range and variability in incorporation of 2AP can be seen in frequency distributions constructed from grain counts. All the curves were positively skewed and covered a wide range, which under these experimental conditions, extended from 0 to 40 counts over the nucleus of cells fixed immediately after 8 hr labeling.