Short Term Effect of Caffeine on Purine, Pyrimidine and Pyridine Metabolism in Rice (Oryza sativa) Seedlings

As part of our studies on the physiological and ecological function of caffeine, we investigated the effect of exogenously supplied caffeine on purine, pyrimidine and pyridine metabolism in rice seedlings. We examined the effect of 1 mM caffeine on the in situ metabolism of C-14-labelled adenine, guanine, inosine, uridine, uracil, nicotinamide and nicotinic acid. The segments of 4-day-old dark-grown seedlings were incubated with these labelled compounds for 6 h. For purines, the incorporation of radioactivity from [8-C-14]adenine and [8-C-14]guanine into nucleotides was enhanced by caffeine; in contrast, incorporation into CO2 were reduced. The radioactivity in ureides (allantoin and allantoic acid) from [8-C-14]guanine and [8-C-14]inosine was increased by caffeine. For pyrimidines, caffeine enhanced the incorporation of radioactivity from [2-C-14]uridine into nucleotides, which was accompanied by a decrease in pyrimidine catabolism. Such difference was not found in the metabolism of [2-C-14]uracil. Caffeine did not influence the pyridine metabolism of [carbonyl-C-14]-nicotinamide and [2-C-14]nicotinic acid. The possible control steps of caffeine on nucleotide metabolism in rice are discussed.