The karyotype of Nothoscordum arenarium Herter (Gilliesioideae, Alliaceae): a populational and cytomolecular analysis

Abstract

The genus Nothoscordum Kunth comprises approximately 20 species native to South America. Karyologically, the genus is remarkable for its large chromosomes and Robertsonian translocations. Variation in chromosome number has been recorded in a few polyploid species and it is unknown among diploids. This study presents the chromosome number and morphology of 53 individuals of seven populations of N. arenarium Herter (2n = 10). In addition, karyotype analyses after C-banding, staining with CMA and DAPI, and in situ hybridization with 5S and 45S rDNA probes were performed in six individuals from one population. All individuals exhibited 2n = 10 (6M + 4A), except for one tetraploid (2n = 20, 12M + 8A) and one triploid (2n = 15, 9M + 6A) plant. C-banding revealed the presence of CMA+ /DAPI - heterochromatin in the short arm and in the proximal region of the long arm of all acrocentric chromosomes. The 45S rDNA sites co-localized with the CMA + regions of the acrocentrics short arms, while the 5S rDNA probe only hybridized with the subterminal region of a pair of metacentric chromosomes. A change in the pattern of CMA bands and rDNA sites was observed in only one individual bearing a reciprocal translocation involving the long arm of a metacentric and the long arm of an acrocentric chromosome. These data suggest that, despite isolated cases of polyploidy and translocation, the karyotype of N. arenarium is very stable and the karyotypic instability described for other species may be associated with their polyploid condition.

Karyological, morphological, and phylogenetic diversification in Leucocoryne Lindl (Allioideae, Amaryllidaceae)

“…Some of the 45S rDNA sites were very small and difficult to visualize (Fig. 2b).The restricted localization of 45S rDNA sites on the short arms of acrocentric chromosomes in all Leucocoryne species confirms the tendency of 45S rDNA sites to occupy mainly the short arms of acrocentric chromosomes, as observed in other species of the tribe Ipheieae (Guerra and Felix 2000, Souza et al 2009.…”

“…The diploids L. purpurea (clade III) and L. vittata (clade IV) have single pairs of subterminal 5S rDNA sites, identical to those observed in diploids of the genus Nothoscordum in the section Inodorum and in N. pulchellum (section Nothoscordum) (Guerra and Felix 2000;Souza et al 2009Souza et al , 2012. The presence of the same karyotypes in species of distinct clades suggests that the ancestral karyotype of clade III and IV would have had the same pattern of rDNA sites as species of Nothoscordum, duplicated faithfully in the tetraploids L. violacescens (clade III) and L. ixioides (clade IV) (Fig.…”

“…Leucocoryne and Nothoscordum are the only genera of the tribe Ipheieae to have diploids with n = 5 with the same karyotype formula and similar distributions of 5S and 45S rDNA sites (Souza et al 2009(Souza et al , 2012, which places this karyotype as the putative ancestral karyotype before divergence ( Fig. 3; Online Resource 3).…”

“…This suggests that the karyotype differentiation of Zoellnerallium occurred through polyploidization events and centric fissions (Crosa 1975(Crosa , 2004. The most evident karyotype differences between Leucocoryne and Nothoscordum refer to the short arm of the acrocentric chromosome of Nothoscordum, which is generally very small (Crosa 1988) and harbors only 45S rDNA sites (Guerra and Felix 2000;Souza et al 2009Souza et al , 2010Souza et al , 2012. The short arms of the acrocentric chromosomes in Leucocoryne are generally larger, being referred to as subtelocentric (st) or telocentric (t) (Crosa 1988;Jara-Arancio et al 2012).…”

“…These species were chosen because they have been previously analyzed with the same citomolecular techniques, which allowed us to make a comparative cytogenetics analysis (Guerra and Felix 2000;Souza et al 2009Souza et al , 2010Souza et al , 2012. The ITS sequences of all species were retrieved from a previous study (see Genbank accessions number in Online Resource 1), except for Nothoscordum pulchellum Kunth.…”