Exogenous nucleosides stimulate RNA synthesis in resting cells of a culture of scarlet rose

RNA synthesis in response to exogenous nucleoside precursors was studied in a suspension culture of rose cells. Exponentially growing and resting cells were prelabeled with 3H] uridine, an excess of unlabeled uridine added, and subsequent isotopic incorporation into nuclear and ribosomal fractions measured. The data were compared to control values in cells continuously labeled in the absence of unlabeled uridine. Addition of uridine to the growing culture reduced the further uptake, and incorporation of 3H] uridine into RNA. In contrast, in resting cells, the addition of uridine (or, purine nucleosides) enhanced the apparent utilization of 3H] uridine in RNA synthesis by 2- to 4-fold.