Purine and pyrimidine metabolism during the partial drying treatment of white spruce (Picea glauca) somatic embryos

The imposition of a partial drying treatment (PDT) on mature white spruce s omatic embryos is a necessary step for successful germination and embryo co nversion into plantlets, Purine and pyrimidine metabolism was investigated during the PDT of white spruce somatic embryos by following the metabolic f ate of C-14-labeled adc nine, adenosine, and inosine, as purine intermediat es, and orotic acid, uridine, and uracil, as pyrimidine intermediates, as w ell as examining the activities of key enzymes. Both the salvage and the de gradation pathways of purines were operative in partially dried embryos. Ad enine and adenosine were extensively salvaged by the enzymes adenine phosph oribosyltransferase and adenosine kinase, respectively. The activity of the former enzyme increased during the PDT, In both mature and partially dried embryos, a large proportion of inosine was recovered as degradation produc ts. The de novo pathway of pyrimidine nucleotide biosynthesis, estimated by the incorporation of orotic acid into tbe nucleotides and nucleic acids, w as high at the end of the maturation period and declined during the PDT, Ur idine was the main substrate for the pyrimidine salvage pathway, since a la rge proportion of uracil was recovered as degradation products, i.e. CO2 an d beta -ureidopropionic acid in both mature and partially dried embryos. Ur idine was mainly salvaged by uridine kinase, whose activity was found to in crease during the PDT, Taken together these results indicate that the PDT m ight be required for increasing the activity; of adenine and uridine salvag e enzymes, which could contribute to the enlargement of the nucleotide pool required at the onset of germination.