Pyrimidine Nucleotide Biosynthesis During Somatic Embryogenesis in a Carrot Cell Suspension Culture

Metabolism of pyrimidine nucleotides was investigated in a synchronous system of somatic embryogenesis of a carrot suspension culture in which RNA turnover was very active at the early stage of the embryogenesis. Incorporation of [6_14 C]orotate, [2-14 C]uracil and [2-C]uridine into the nucleotide and nucleic acid fractions was higher in the embryogenic than in the non-embryogenic cells. 14 The activity of orotate phosphoribosyltransferase (OPRTase)plus orotidine-S'-monophos­phate decarboxylase (ODCase), uridine kinase (UKase), phosphoribosylpyrophosphate synthetase (PRPPSase), glucose-6-phosphate dehydrogenase (G6PDH), and -phosphogluconate dehydrogenase (6PGDH)was higher in the embryogenic cells, while the uracil phosphoribo syltransferase (UPRTase)level in the embryogenic cells was similar to that in the non-embryo­genic cells. The results obtained here indicate that both the activity of the «de novo» and «salvage» pathways of pyrimidine nucleotide biosynthesis increase during embryogenesis, which supply building blocks for active RNA synthesis.