Karyological Features of <i>Achyrocline</i> (Asteraceae, Gnaphalieae): Stable Karyotypes, Low DNA Content Variation and Linkage of rRNA Genes

Abstract

Many Achyrocline (Asteraceae, tribe Gnaphalieae) species are widely used in Argentina, Brazil and Uruguay as popular medicinal and aromatic plants. Achyrocline flaccida, A. satureioides, A. alata, and A. crassiuscula are distributed in Uruguay and popularly known as ‘marcelas’. In order to characterize them, we performed chromosome counts, compared the karyotypes, mapped the 5S and 45S rDNA sites by fluorescent in situ hybridization, and estimated their DNA content. All species were diploid with 2n = 28 chromosomes, this being the first report for A. flaccida and A. crassiuscula. All species showed symmetrical karyotypes composed exclusively of biarmed chromosomes. DNA content estimated by flow cytometry revealed 2C values ranging from 5.73 to 6.03 pg, the amounts for A. alata and A. crassiuscula being higher than those for the other species. Cytogenetic mapping of 5S and 45S rDNA sequences in three species, A. flaccida, A. satureioides and A. alata, showed that in these species both sites co-localized in the pericentromeric region of chromosome 10. This site corresponds to the only DAPI^– and CMA⁺ band of their genomes. Southern blot hybridization of 5S and 45S rDNA on BamHI digested genomic DNA confirmed the tight linkage of these rDNA families into a single unit. Cytological data indicate that Achyrocline species are karyologically poorly differentiated, whereas the uncommon distribution of 5S and 45S rDNA suggests a close relationship with other genera of the Anthemidae tribe.

Intra- and interspecific chromosome polymorphisms in cultivated Cichorium L. species (Asteraceae)

“…This association has also been previously described for Asteraceae (Fregonezi et al , 2004; Mazzella et al , 2010; Salles-de-Melo et al , 2010) and has been shown to be quite frequent within angiosperms (Guerra, 2000). On the other hand, the occurrence of CMA + bands in association with 5S rDNA sites in the family has been mainly associated with the co-localization of 45S and 5S rDNA sites, as observed for species of Achyrocline (Mazzella et al , 2010) and Artemisia (Pellicer et al , 2008; Konowalik et al , 2010). Moreover, as occurred for both species herein analysed, Hypochaeris catharinensis Cabrera also showed co-localization of CMA + bands and 5S rDNA (Reck et al , 2011), a feature described for other higher plants ( e.g.…”

“…(subfamily Asteroideae) Hypochaeris spp. (subfamily Cichorioideae), which may also be evidences of structural changes (such as paracentric inversions) throughout chromosome evolution within these plant groups (Cerbah et al , 1998; Ruas et al , 2005; Mazzella et al , 2010). …”

Linked 5S and 45S rDNA Sites Are Highly Conserved through the Subfamily Aurantioideae (Rutaceae)

“…In most species, the loci for 5S and 45S rRNA genes are located in different chromosomes, whereas in other species the 2 loci are found in the same chromosome pair, sometimes closely linked to each other, as observed for example in different species of Brassica [Hasterok et al, 2006], Aristolochia [Berjano et al, 2009] and Rhynchospora [Sousa et al, 2011]. A completely different kind of association, where a single repeat unit contains both rDNA families, first reported in some members of the daisy family Asteraceae [García et al, 2009;Mazzella et al, 2010] and in the gymnosperm Ginkgo biloba [Galián et al, 2012], may be more common than initially thought.…”

Karyotype characterization reveals an up and down of 45S and 5S rDNA sites in Crotalaria (Leguminosae-Papilionoideae) species of the section Hedriocarpae subsection Macrostachyae

“…A similar condition was observed in the genus Achyrocline (Asteraceae) where both 45S and 5S rDNA were mapped linked and near to the pericentromeric region of chromosome 10 and the karyotypes were quite similar. However, the ribosomal sites could appear in different configurations, in the same or in different chromosomes, making important a comparison with phylogenetic related species (Mazzella et al 2010).…”