Abstract
The location of 5S and 35S rDNA sequences in chromosomes of four Aconitum subsp. Aconitum species was analyzed after fluorescence in situ hybridization (FISH). Both in diploids (2n = 2x = 16; Aconitum variegatum, A. degenii) and tetraploids (2n = 4× = 32; A. firmum, A. plicatum), rDNA repeats were localized exclusively on the shorter arms of chromosomes, in subterminal or pericentromeric sites. All analyzed species showed similar basal genome size (Cx = 5.31–5.71 pg). The most striking features of tetraploid karyotypes were the conservation of diploid rDNA loci and emergence of many additional 5S rDNA clusters. Chromosomal distribution of excessive ribosomal sites suggests their role in the secondary diploidization of tetraploid karyotypes.
Highlights
Almost all Aconitum species studied so far have an interesting bimodal karyotype (x = 8) with two large and six small chromosomes (Yuan and Yang 2006, Hong et al 2017)
From three diploid taxa belonging to the subgenus Aconitum, A. degenii and A. lasiocarpum showed a heterochromatin-poor karyotype with relatively stable C-banding patterns, while A. variegatum generally showed a higher amount of heterochromatin (Joachimiak et al 1999)
Four of them were localized on chromosomes 3 and 5, one on chromosome 1 and one on chromosome 7 (Figs. 1c, d and 2b). 35S rDNA clusters on chromosomes 1, 3, and 5 seem to be the major nucleolar-organizing regions (NORs) in the analyzed plants
Summary
Two high-mountain tetraploid species belonging to this subgenus, Western Carpathian A. firmum and Sudetic A. plicatum, contained different amounts of heterochromatin (Mitka et al 2007). This suggests that Aconitum karyotypes, stable at the level of chromosome morphology, are differentiated at the intrachromosomal level. The existence of such differences has much potential use in taxonomical and phytogeographical studies of Aconitum, especially because of the general lack of reproducible, species-specific molecular markers within this genus. Some arbitrarily amplified sequences (RAPD, ISSR) seem to be useful for the estimation of molecular diversity of target Aconitum genomes (Fico et al 2003; Zhang et al 2005; Mitka et al 2007), low reproducibility and the generation of dominant, non-locus-specific markers limit the broader applicability of these methods in phylogenetic studies
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