Biosynthesis of pyrimidine nucleotides and arginine in a suspension culture of Catharanthus roseus

Abstract

1. 1. The intracellular levels of pyrimidine nucleotides and of arginine changed markedly during the growth cycle (10 days) of Catharanthus roseus in suspension culture. 2. 2. The levels of UTP and UDP-glucose increased rapidly during the 24 hr which followed transfer of the cells to fresh Murashige-Skoog medium. The levels of other pyrimidine nucleotides also increased after the transfer of cells, but the maximum level of UMP was detected on day 5. 3. 3. The level of free arginine decreased just after subculture, although the level of arginine, which had been incorporated into protein, increased during the logarithmic phase of cell growth. Ornithine could not be detected at any stage of growth of the cells. 4. 4. The label from NaH 14CO 3 was incoprorated into pyrimidine nucleotides and into the guanido group of arginine. Most of the radioactivity of these compounds was associated with nucleic acids and proteins. 5. 5. The contribution of de novo synthesis of pyrimidine nucleotides was higher in the early phases of cell growth than in the stationary phase. In contrast, the maximum incorporation of NaH 14CO 3 into arginine was found during the cell division phase when active synthesis of proteins occurred. 6. 6. The mechanisms which regulate the biosynthesis of pyrimidine nucleotides and arginine in vivo are discussed.