Citogenética em espécies do gênero Eichhornia Kunth, Pontederiaceae Kunth

Abstract

Eichhornia is a Neotropical genus belonging to the family Pontederiaceae. It occurs in aquatic environments with outstanding ecological importance. Chromosome studies in the genus are scarce, limited to the description chromosome numbers. This study aimed to analyze four species of Eichhornia, by conventional Giemsa staining, fluorochrome staining with CMA and DAPI and fluorescent in situ hybridization (FISH), to characterize the karyotypes and define numerical or structural karyotypic polymorphisms that could contribute to interspecific differentiation between these four species and the understanding of chromosome evolution of the genus Eichhornia. All species have small chromosomes and symmetrical karyotypes, from 0.73 μm in E. crassipes to 2.94 μm in E. heterosperma and predominantly metacentric. Chromosomal counts were 2n = 32 for E. crassipes, 2n = 30 for E. heterosperma, 2n = 28 for E. diversifolia and 2n = 16 for E. paniculata. The investigated species showed interphase nuclei ranging from areticulate to semi-reticulate and proximal early condensation in prophase chromosomes with most intense staining in pericentromeric regions. The CMA/DAPI staining revealed CMA+/DAPI- bands that were co-localized with 45S rDNA sites in terminal regions. Two signals were observed for E. heterosperma and E. diversifolia, and four signals in E. paniculata and E. crassipes, although six CMA+ signals were observed in the latter species. The 5S rDNA did not vary in the number of sites but in position. Two sites were observed in the terminal region in E. paniculata and in the pericentromeric region in the other species. Chromosomal inversion and dysploidy were suggested to explain the non-colinearity of 5S rDNA sites.