Determinação do número cromossômico e da heterocromatina em espécies de leguminosae

Abstract

The Leguminosae family comprises 20,000 species divided into 807 genera and occurs in all ecosystems. It ranks among the three families with the greatest diversity across all phytogeographic domains of Brazil, with more than half of its species being endemic. Currently, it is divided into six subfamilies: Cercidoideae, Detarioideae, Duparquetioideae, Dialioideae, Caesalpinioideae, and Papilionoideae. Among these subfamilies, Caesalpinioideae stands out for exhibiting chromosome numbers of 2n = 24, 26, and 28, with literature records of 2n = 14, 16, 52, 54, and 56. For taxonomically stable groups, such as most legumes, simple chromosome counts generally provide limited information, except in species that exhibit variability in chromosome size and morphology. Given this, the study aimed to determine the chromosome number and identify the heterochromatin composition in species belonging to subfamily Caesalpinioideae (Leguminosae). For mitotic analyses, root tips were pretreated with 8- hydroxyquinoline (8Hq) and then fixed in Carnoy’s solution. Slides were prepared using the acetic acid (60%) squash method and stained with the fluorochromes CMA/DAPI. The best slides were stained with CMA/DAPI and photographed using an epifluorescence photomicroscope. Seven species belonging to the genera Albizia, Enterolobium, Inga, Pithecellobium (new record to Pithecellobium diversifolium 2n = 26,), Pityrocarpa, and Prosopis were analyzed, with chromosome numbers varying between 2n = 26 and 2n = 28. Regarding heterochromatin composition, all analyzed species exhibited CMA+ bands, indicating GC-rich regions. The observed heterochromatin bands were located in pericentromeric and terminal regions. Chromosome number and heterochromatin composition are determining factors in the speciation processes of Leguminosae, as the location and distribution of heterochromatin among related taxa may represent evolutionary adaptations to distinct ecological niches.