Classical and Molecular Cytogenetic Tools to Resolve the Bixa Karyotypes

Abstract

SummaryThe cytogenetic studies performed in Bixa orellana have reported 2nϭ14 or 2nϭ16 chromosomes with little karyotypic information. In this context, an improved cytogenetic protocol using enzymatic maceration of meristematic cellular walls and digital image analysis was applied to B. orellana and B. arborea. In B. arborea, the high-resolution technique, Ag-NOR and C banding methods, and FISH using a probe of 45S rDNA genes, were also performed. Prometaphasic and standard C-metaphasic chromosomes presented well-defined primary and secondary constrictions facilitated the pairing of homologues and assembly of the karyogram for the 2 species. These species showed similar karyotypes with 2nϭ14 chromosomes, being composed of 5 metacentric pairs (1, 2, 3, 4 and 6) and 2 submetacentric pairs (5 and 7). The chromosome 1 is approximately 2 times as long as the others and possesses the secondary constriction adjacent to the centromere, which suggests that Robertsonian translocation between 2 smaller chromosomes may have occurred during the karyotype evolution of Bixa. Additionally, the active NOR, the NOR-adjacent heterochromatic region and 18S, 5.8S and 26S rDNA genes were identified in the secondary constriction of chromosome 1.

Cytogenetics and Reproductive Biology of <i>Bixa orellana</i> L. (Bixaceae)

“…5). The result of FISH with 45S rDNA probe also confirms this location, as previously reported by Almeida et al (2006). The localization of the two CMA positive bands presented here agrees with the localization of 45S rDNA and NOR.…”

“…The haploid and diploid numbers observed and the karyomorphological data obtained agree with those presented in the literature (Hanson et al 2001, Almeida et al 2006. The mitotic chromosomes observed were small (1.4-3.2 μm) and mainly metacentric.…”

“…The mitotic chromosomes observed were small (1.4-3.2 μm) and mainly metacentric. Almeida et al (2006) presented chromosomes ranging from 1.2 to 3.8 μm with five metacentric and two submetacentric chromosome pairs (5m+2sm) instead of the 6m+1sm presented here. Intraspecific karyomorphological variation is quite common in plants.…”

“…Simmonds (1954) and Krishnan and Ayyangar (1987) reported 2n=16 while Mukherjee (1975) reported 2n=14. Almeida et al (2006) proposed the diploid chromosome number 2n=14, reporting the first cytomolecular data for the species with the chromosomal localization of 45S rDNA site. These authors presented a bimodal karyotype, with one pair of chromosomes significantly longer than the others.…”

Karyotype and nuclear DNA content of Psychotria ipecacuanha: a medicinal species

“…Identical results were obtained in Zea mays Saraiva 1993, 1997), Coffea canephora , Bixa orellana (Almeida et al 2006), Glycine max (Clarindo et al 2007) and Paullinia cupana (Freitas et al 2007). We considered these methodologies to be fundamental, as they supply more adequate chromosomic preparations in comparison with those yielded by the squashing technique (Carvalho and Saraiva 1993), usually applied in cytogenetic studies of ipecac (Assis and Giulietti 1999, Rout et al 2000, and Souza et al 2006).…”