Metabolic Fate of [8-14C]Adenine and [8-14C]Hypoxanthine in Higher Plants

Abstract

Summary Metabolism of [8- 14 C]adenine and [8- 14 C]hypoxanthine was studied in several plant materials including cotyledons and embryonic axes of black gram seedlings, shoots of light- and darkgrown pea seedlings, young leaves and calluses of tobacco, phloem and xylem tissues of mature carrot roots, suspension culture cells of carrot, leaves of Ginkgo biloba and Acer buergerianum and shoot of wheat seedlings. In all plant materials examined, the «salvage» pathways of adenine and hypoxanthine for nucleotides and nucleic acids were present and the «adenine salvage» pathway was more active than the «hypoxanthine salvage» pathway. In addition to the «salvage» pathways, adenine and hypoxanthine were degraded to allantoin, allantoic acid and CO 2 . The rate of degradation of hypoxanthine was higher than that of adenine in all plant material examined. A large accumulation of allantoin and allantoic acid was observed in seedlings of black gram and peas, tobacco calluses, carrot suspension culture cells and leaves of Ginkgo and Acer . In contrast, little incorporation o£ radioactivity of labelled purines into allantoin and allantoic acid was found in xylem and phloem of carrot roots and tobacco leaves. A large quantity of 14 CO 2 release from [8- 14 C]hypoxanthine was observed in the leaves of tobacco, Ginkgo and Acer and wheat shoots. The data suggest that adenine and hypoxanthine are used for nucleotide and nucleic acid biosynthesis in all plant species. Adenine and hypoxanthine are also degraded in all plant species, but the end products of purine catabolism were different in each organ and tissue of plants. Accumulation of allantoin and allantoic acid may occur in leguminous plants and cultured tissues and cells. A strong degradation system of allantoin and allantoic acid may be present in leaf tissues.