Purine nucleotide and RNA synthesis in suspension cultured cells of carrot

Purine nucleotide and RNA synthesis have been investigated at the different growth stages of carrot (Daucus carota L.) cells grown in suspension cultures. At the early growth stages an increase in the content of RNA was observed, although at later stages RNA was degraded. The highest rates of incorporation of [14C]‐labelled adenosine into ATP and GTP were observed at the late growth sttages. This indicated that purine slavage was more importnt at the late growth stages, while de novo synthesis was dominant during the initial growth stages. This pattern was also reflected by increased levels, in the cell dividison phase, of theenzymes glycinamide ribonucleotide synthetase (EC 6.3.1.3.) and phosphoribosylpyrophosphate amido‐transferase (EC 2.4.2.14) involved in de novo purine synthesis. The activities of the purine salvage enzymes varied little during growth. Cells in the stationary phase, that were starved for sucrose and phosphate, showed a dramatic increase in cellular metabolism, as judged from a rapid uptake and incorporation of [32P]‐labelled phosphate into nucleotides and RNA, when incubated in fresh medium.