Transcriptional Activities of the Chloroplast-Nuclei and Proplastid-Nuclei Isolated from Tobacco Exhibit Different Sensitivities to Tagetitoxin : Implication of the Presence of Distinct RNA Polymerases

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We examined the effects of tagetitoxin, a potent inhibitor of RNA polymerases from chloroplasts and Escherichia coli, on the transcriptional activities of chloroplast- and proplastid-nuclei(nucleoids) isolated from mature tobacco(Nicotiana tabacum L.) leaves and cultured tobacco cells(line BY-2), respectively. Transcription by the isolated chloroplast-nuclei was effectively inhibited by tagetitoxin(95-99% reduction at 10 μM tagetitoxin), but transcription by the isolated proplastid-nuclei was only partially inhibited(40-50% reduction) by this compound. Southern hybridization experiments revealed that the transcription of various plastid genes (psbA, atpA, rpoB, psaA/B, atpB, rbcL, petB, rpl16, and rrn23) was sensitive to tagetitoxin in the isolated chloroplast-nuclei, whereas the transcription of the same genes was relatively resistant to this compound in the isolated proplastid-nuclei. These results suggest that; (i)distinct RNA polymerase activities with different sensitivities to tagetitoxin are present in plastids, (ii)a tagetitoxin-sensitive RNA polymerase is the major RNA polymerase in chloroplasts whereas a tagetitoxin-insensitive enzyme is major in proplastids, and (iii)both RNA polymerases can transcribe various plastid genes.
日本植物生理学会の論文