Spatial expression of DNA topoisomerase I genes during cell proliferation in

SUMMARYThe spatial expression of carrot (Daucus carotaL.)top1genes encoding the two isoforms of the enzymeDNA topoisomerase I (EC 5.99.1.2) was investigat-ed. In situhybridization analysis performed with aprobe recognizing both top1transcripts providedevidence that in explanted hypocotyls induced toproliferate in vitroby the addition of the growth reg-ulator 2,4-dichlorophenoxyacetic acid (2,4-D), themRNA accumulation parallels the proliferation ofprovascular cells of the stelar cylinder. Duringsomatic embryogenesis, the histological distributionof top1transcripts was strongly evident at the stageof torpedo-shaped embryos, but gene expression wasnot only restricted to meristematic regions. When thespatial localization was extended to carrot vegetativeapices and the investigation was carried out withspecific probes for top1aand top1b, both transcriptspreferentially accumulated in tissues having mitoticactivity.INTRODUCTIONIn plants, the understanding of molecular eventsthat regulate cell division is relevant for studies