Studies on the Growth in Culture of Plant Cells: XV. UPTAKE AND UTILIZATION OF URIDINE DURING THE GROWTH OF ACER PSEUDOPLATANUS L. CELLS IN SUSPENSION CULTURE

Abstract

[2-¹⁴C]-uridine is rapidly taken up by sycamore cells in suspension culture. A proportion of the radioactivity enters RNA without measurable delay, whilst the remainder equilibrates with a large pool of phosphorylated compounds, the major radioactive component of which is 5'-UMP. Both the uracil and cytosine residues of RNA receive label from [¹⁴C]-uridine and, when the cells are supplied with high concentrations of uridine, these bases are derived almost exclusively from the nucleoside. [¹⁴C]-uridine is incorporated into RNA at all stages of the growth cycle of batch cultures; its continuing incorporation, when the total RNA content of the cells is rapidly decreasing, indicates a high rate of turnover of the total RNA. Long-term labelling experiments also indicate turnover of RNA during the phase of active cell division and suggest that a large proportion of the degradation products are not re-utilized for RNA synthesis. Sycamore cells degrade [2-¹⁴C]-uridine with release of ¹⁴CO₂. The proportion degraded increases from 25 per cent at an external uridine concentration of 10⁻⁶M to 75 per cent at 10⁻³ M. Despite this, nucleic acids are the only macromolecules that receive a significant amount of radioactivity from [2-¹⁴]C-uridine.