Karyological Observations in Medicago Section Dendrotelis (Fabaceae)

Abstract

Medicago section Dendrotelis comprises polyploid, woody shrubs restricted to rocky and cliff faces in coastal places of the Mediterranean basin, showing a very close morphology. This has resulted in controversial taxonomic studies, differing in the circumscription and number of recognized species (from one to three). In the present study, cytogenetic studies (meiotic analysis, C-banding, Ag-NOR banding) were made in M. arborea, M. strasseri, and M. citrina to determine their karyological and evolutionary relationships. The observation of meiocytes revealed a regular meiotic cycle in all species. At pachytene stage, chromosomes showed constitutive heterochromatic blocks (knobs) that were species-specific, and clearly discriminate M. arborea and M. strasseri from M. citrina. Conventional karyotypes of M. strasseri and M. arborea were similar concerning chromosome classes, the apparent chromosome length, and the morphology of the single NOR chromosome pair. However, C-banding technique revealed karyotypic differences between both species. In contrast, M. citrina exhibited a slightly asymmetric karyotype, the presence of two pairs of chromosomes showing secondary constrictions, a similar apparent chromosome length, and two pairs of active rDNA loci. Its C-banded karyotype strikingly differed from those observed in M. arborea and M. strasseri, and only three chromosome pairs showed heterochromatic blocks. These cytogenetic data indicate a clear evolutionary split in woody medics (tetraploid vs hexaploid species), reflecting divergent patterns of karyological evolution. Taken together, all karyological data unequivocally support the recognition of M. citrina as a distinct species.

Conserved Organisation of 45S rDNA Sites and rDNA Gene Copy Number among Major Clades of Early Land Plants

“…Silver impregnation was carried out on 1–2 day-old preparations according to the protocol described in Rosato and Rosselló [ 31 ]. Slides were incubated with a few drops of freshly prepared 50% silver nitrate solution and covered with a nylon mesh, and incubated in a humid chamber at 55–60°C for 1–2 h. After washing in distilled water, slides were stained with 4% Giemsa solution for 5 min., quickly rinsed in distilled water, air-dried, and mounted in 50% glycerol solution.…”

Evolutionary site-number changes of ribosomal DNA loci during speciation: complex scenarios of ancestral and more recent polyploid events

“…In the case of V. lucentina , immature inflorescences were directly fixed in an ethanol–glacial acetic acid (3 : 1) mixture and stored at 4 °C until required to study the male meiotic divisions according to the protocol described above. AgNO 3 staining using silver impregnation was carried out on 1–2 day-old chromosome preparations according to the protocol described in Rosato and Rosselló (2009) .…”

Seed image analysis provides evidence of taxonomic differentiation within the Medicago L. sect. Dendrotelis (Fabaceae)

“…It was first described as a pale, yellowflowered variety of M. arborea (Font Quer, 1924), and concerns about its specific status have been reported by several authors (Bol os & Vigo, 1974;Lesins & Lesins, 1979;P erez-Bañ on, Juan, Petanidou, Marcos-Garc ıa, & Crespo, 2003;Small & Jomphe, 1989). Taken together, all the karyological data unequivocally support the recognition of M. citrina as a distinct species (Rosato & Rossell o, 2009).…”