Potentiation by Dihydrothymine of 5-Fluorouracil Inhibition during Chloroplast Development and RNA Synthesis in Euglena gracilis1)

Abstract

Summary In Euglena gracilis 5-fluorouracil is degraded reductively as measured by the 14CO2 release from the [2-14C]-labeled analog and is anabolized into 5-fluoronucleotides, which were found to be incorporated into RNA. This incorporation is enhanced during light-induced chlororplast synthesis. Dihydrothymine is shown to be an effective inhibitor of 5-fluorouracil degradation, thus enhancing its incorporation into nucleotides as well as RNA. This enhanced incorporation was observed as an increased incorporation into cytoplasmic rRNA, but other RNA-species were not improved. Under non-growing conditions, which were used to exclude the observed inhibitory effect of 5-fluorouracil on growth of E. gracilis, synthetic processes during chloroplast development, such as chlorophyll synthesis, photosynthetic CO2-fixation, and light-induced RNA-formation measured as [5-311]-nracil incorporation were inhibited by 5-fluorouracil. These inhibitions were enhanced in the presence of dihydrothymine. This potentiation of 5-fluorouracil incorporation into cytoplasmic and chloroplastic rRNA's in plants is discussed.