Chloroplast Development in 4-Thiouridine-Cultured Radish Seedlings XI. Inhibition of RNA Synthesis by 4-Thiouridine Nucleotides during Germination of Radish Seeds

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The effects of 4-thiouridine and its metabolites on RNA synthesis in radish (Raphanus sativus) cotyledons were investigated. The 4-thiouridine nucleotides, 4-thioUTP and 4-thioUDP, were found to inhibit DNA-dependent RNA polymerase activities of isolated nuclei and of chloroplasts from radish cotyledons. These inhibitors appeared to compete with UTP for its binding to RNA polymerase. Neither 4-thiouridine nor 4-thioUMP inhibited RNA polymerase activities. Reduced RNA accumulation accompanied by the inhibition of protochlorophyllide accumulation was observed in cotyledons of dark-grown radish seedlings germinated and grown with 4-thiouridine. On the other hand,4-thiouridine had no effect on chloroplast development in the control seedlings germinated and grown without 4-thiouridine. These results suggest that the inhibition of chloroplast development by 4-thiouridine may in part be due to the inhibition of RNA synthesis by 4-thiouridine nucleotide during germination, resulting in inhibition of etioplast development.
日本植物生理学会の論文