Purine metabolism during white spruce somatic embryo development: salvage of adenine, adenosine, and inosine

Contribution of the adenine, adenosine and inosine salvage to the purine nu cleotide and nucleic acid biosynthesis during white spruce (Picea glauca) s omatic embryo maturation was estimated by in situ assays using [8-C-14]aden ine, [8-C-14]adenosine and [8-C-14]inosine. The salvage of adenine and aden osine was high during the initial stages of embryo maturation, characterize d by rapid cell proliferation, but it declined upon further embryo developm ent. Inosine salvage activity was always much lower than that observed for adenine and adenosine. Consistent with these results, activities of adenine phosphoribosyltransferase (APRT) and adenosine kinase (AK) measured in the embryo extracts in vitro were much higher than the activity of inosine kin ase (IK) during all stages of embryo development. Utilization of adenosine and inosine for nucleotide and nucleic acid synthesis was found to be regul ated by the enzymes AK and IK, as the pattern of their activities was very similar to the activity of adenosine and inosine salvage, estimated with ex ogenously supplied precursors. However, little correlation between salvage of adenine and activity of APRT was found throughout somatic embryo maturat ion. As no adenosine nucleosidase activity was found in white spruce embryo s, adenosine, but not adenine, seems to be the major end product of adenyla te catabolism and becomes the predominant substrate for purine salvage in v ivo. Thus, adenosine salvage appeared to have the most important role in wh ite spruce embryos. Studies on the metabolic fate of [8-14C]adenine and [8- C-14]adenosine suggest that turnover of adenine nucleotides is rapid, as so me of them are utilized for nucleic acid synthesis. In contrast, most of [8 -C-14]linosine taken up by the embryos seems to be directly catabolized by the conventional purine catabolic pathway via ureides in all stages of embr yo maturation. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.