DETERMINAÇÃO DO NÚMERO CROMOSSÔMICO E COMPOSIÇÃO DA HETEROCROMATINA EM ESPÉCIES DA SUBTRIBO Pleurothallidinae Lindl. (Orchidaceae) AREIA –

Abstract

Pleurothallidinae is one of the largest subtribes of the Orchidaceae family, with about 4.570 species and a morphologically variable group. However, it is poorly studied in both chromosomal and heterochromatic bands. Therefore, this work aims to determine the chromosome number and to identify the composition of heterochromatic bands in Brazilian species of the subtribe Pleurothallidinae. The species analyzed had root tips pretreated with paradychlorobenzene (PDB) and slides were prepared by the acetic acid crushing method, and then stained with CMA/DAPI fluorochromes. Chromosome numbers varied from 2n = 20 in two species of Specklinia to 2n = 40 in three species of Acianthera, with a mean chromosome size ranging from 1.3μm to 2.8μm. Regarding the morphology of the karyotype, metacentric and submetacentric chromosomes predominated for all species, except for Anathallis rubens, which presented a small acrocentric pair. In general, the karyotypes were relatively symmetrical, except for an indeterminate species of Anathallis that presented a strongly bimodal karyotype, being seven pairs of larger chromosomes and 12 pairs of smaller chromosomes. The use of the double staining technique with fluorochromes allowed the identification of four patterns of heterochromatic bands: CMA+/DAPI-, CMA+/DAPI0, DAPI+/CMA- e DAPI+/CMA0, varying in number, location and size between species and the studied genus. However, the species Anathallis rubens did not observe any heterochromatic bands and all species of the genus Stelis presented a heteromorphic band CMA+ by monoploid complement. The species analyzed here presented heterochromatic bands CMA+ and DAPI+, being the identification of the heterochromatic composition an important cytotaxonomic appliance for the group.