Análise comparativa entre métodos de bandeamento cromossômico em espécies de aristolochia seção gymnolobus (Aristolochiaceae)

Abstract

The family Aristolochiaceae comprises about eight genera and 620 species, predominantly found in tropical and subtropical regions worldwide. In Brazil, the genus Aristolochia is the only one recognized, with 83 species, of which 37 are endemic. The most likely basic chromosome number for Aristolochia is x = 7, with a wide range of chromosome number variation recorded, including 2n = 6, 8, 10, 12, 14, 24, 26, 28, 32, and 36. This research aimed to characterize the karyotypes of two species of Aristolochia occurring in the Northeast region of Brazil, through a comparison of banding methods using double staining with fluorochromes CMA/DAPI and C-banding technique. For chromosome analysis, root tips were pre-treated with 8-hydroxyquinoline at 10°C for 24 hours, fixed in Carnoy solution, and slides prepared by enzymatic digestion using the squashing method with 60% acetic acid. Slides were then stained with fluorochromes CMA/DAPI and subsequently subjected to C-banding. The best cells were Zeiss epifluorescence photomicroscope equipped with AxioCam MRC5 video camera with the aid of Axiovision 4.8 software. Aristolochia gigantea and Aristolochia triloba exhibited 2n = 14 chromosomes, with slightly asymmetrical karyotypes, mainly composed by metacentric and submetacentric chromosomes, along with a pair of acrocentrics. Our analysis revealed the occurrence of a pair of terminal CMA+/DAPI− bands in both species and two proximal CMA+/DAPI0 bands in A. gigantea. Conversely, C-banding revealed 12 pericentromeric bands in A. gigantea and 14 in A. trilobata. The genus Aristolochia is known for its high karyotypic variability. However, the Gymnolobus section presents relatively stable characteristics, such as the chromosome number 2n = 14 and the presence of a larger chromosome pair in most species. Our data suggest that C-bands are useful chromosome markers for identifying homologous chromosomes in the section. C-banding revealed the occurrence of pericentromeric constitutive heterochromatin that were not detected by double staining with fluorochromes CMA and DAPI.