Distribuição da heterocromatina em acessos do gênero Agave L.

Abstract

The genus Agave L. belongs to the family Asparagaceae and comprises about 200 species. The main economic interest is in relation to the production of low cost hard fiber, used in various sectors of the economy, and extracted mainly from the species Agave sisalana, known as sisal and A. fourcroydes, known as henequen. The main economic interest is in relation to the production of low cost hard fiber, used in various sectors of the economy, and extracted mainly from the species Agave sisalana, known as sisal and A. fourcroydes, known as henequen. Most of the cytogenetic studies in Agave have been carried out based only on conventional techniques, with the work with chromosome banding considerably reduced. Some recent genomic studies show that the amount of repetitive DNA in Agave corresponds to about 70%. However, the use of base-specific fluorochromes and in situ hybridization with 5S and 45S DNA probes have revealed a much reduced amount of heterochromatin relative to the size of the genome. The objective of this work was to characterize the karyotype of the four accesses of Agave from the germplasm bank of EMBRAPA, mainly to locate heterochromatic chromosomal regions. For this the conventional technique of C-banding and the fluorochromes cromomycin A3 (CMA) and 4, 6 'diamidino-2-phenylindole (DAPI) were used. Conventional staining revealed that the RN hybrid and the Tanzania hybrid are diploids with (2n = 60), A. fourcroydes is a tetraploid (2n = 120) and the ornamental Sisal access is a pentaploid (2n = 150). The chromosomes have irregular chromosome condensation. The double staining with CMA / DAPI revealed variation in the amount and location of CMA+ bands. Among the accessions were four CMA positive bands on A. fourcroydes only on large chromosomes, four bands on RN and Tanzania hybrids on large and small chromosomes, and eight bands on Sisal Ornamental on large and small chromosomes. The C-band pattern was similar in number and location to the CMA+ standard. However, small heterochromatic dots were visualized by the C-band technique in the Tanzania hybrid. These small marks were not evidenced by the fluorochromes and nor mentioned in the literature in other studies. Both the CMA/DAPI chromosomal banding and the C banding technique contributed to the differentiation of the accessions.