| Research Abstract |
1. Catabolism of adenine nucleotides in suspensionーcultured plant cells.
Profiles of the catabolism of adenine nucleotides in cultured plant cells were investigated. Adenine nucleotides, prelabelled by incubation of suspension-cultured Catharantus roseus cells with [8_--^<14>C]adenosine, were catabolized rapidly and most of the radioactivity appeared in ^<14>CO_2. Allantoin and allantoic acid, intermediates of the oxidative catabolic pathway of purines, were temporarily labelled. When the cells, prelabelled with [8_--^<14>C]adenosine, were incubated with high concentrations of adenosine, the rate of catabolism of adenine nucleotides increased. The results suggest that the relative rate of catabolism of adenine nucleotides is strongly dependent on the concentration of adenine nucleotides in the cells. Studies using allopurinol, coformycin and tiazofurin, inhibitors of enzymes involved in purine metabolism, suggest the participation of AMP deaminase and xanthine oxidoreductase in the cata
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bolism of adenine nucleotides in plant cells. AMP deaminase was found in extracts from C. roseus cells and its activity increased significantly in the presence of ATP. In contrast, no adenosine deaminase or adenine deaminase activity was detected. Qualitative differences in the catabolic activity of AMP were observed between suspensionーcultured cells from different species of plants.
2. Adenine metabolism and the synthesis of purine alkaloids in flowers of Camellia
Concentrations of purine alkaloids in stamens and petals of Camellia plants were determined. Caffeine was present in both stamens and petals, but significant amounts of theobromine were found only in the stamens of C. sinensis. In C. irrawadiensis, theobromine accumulated both in stamens and in petals. In contrast, no purine alkaloid was detectable in flower buds of C. japonica and C. sasanqua. The pattern of accumulation of purine alkaloids in the flower buds of a hybrid plant (C. sinensis x C. japonica) was similar to that of C. sinensis, but concentrations of the alkaloids were lower. Tracer experiments using[8_-^<14>C]adenine indicated that the biosynthetic pathway to caffeine was operative in the stamens and petals of C. sinensis and of the hybrid, but the reaction from theobromine to caffeine was deficient in C. irrawadiensis, while the entire series of reactions required for the synthesis of purine alkaloids was deficient in both C. japonica and C. sasanqua. Conventional 'salvage' and degradation pathway for purines were present in the stamens and petals of all Camellia plants examined, but the flux of the degradation pathways was generally higher in Camellia plants that did not accumulate purine alkaloids than in the flowers of the alkaloidproducing species. Less
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