Autosomal and sex chromosomal polymorphisms with multiple rearrangements and a new karyotype in the genus Rhipidomys (Sigmodontinae, Rodentia)

Two diploid numbers and five karyomorphs were found in ten specimens of Rhipidomys (Sigmodontinae, Rodentia) from three states in Brazil: 2n = 50 from Amazonas, and 2n = 44 from Mato Grosso and Bahia. CBG, GTG, and RBG-banding and Ag-NOR analyses were performed, as well as fluorescence in situ: hybridization with (T2AG3)7 probes. The new diploid number of 2n = 50 was associated with two different fundamental numbers (FN = 71 and 72) as a result of pericentric inversions and addition/deletion of constitutive heterochromatin. The samples from two localities (Aripuan? and Vila Rica) in the state of Mato Grosso shared 2n = 44 and FN = 52, but their karyotypes differed because of pericentric inversions. Although the single specimen from Bahia had the same diploid number as the samples from Mato Grosso, its karyotype and FN were completely distinctive. Karyological comparison of GTG-banding patterns revealed total homology between the karyotypes of the specimens from Bahia and Mato Grosso, implying the occurrence of 14 autosomal pericentric inversions. Homologies between ten of the autosomes in the karyotypes with 2n = 50 (FN = 72) and 2n = 44 (from Vila Rica, MT) were demonstrated. The differentiation between 2n = 44 and 2n = 50 involved five pericentric inversions, addition/deletion of constitutive heterochromatin in both autosomes and sex chromosomes, at least one Robertsonian rearrangement and other not detected rearrangements. Despite the remarkable number of rearrangements, interstitial telomeric sites (ITS) were not detected. Sex chromosomes also exhibited polymorphism in size and morphology.     

FISH-aimed karyotype analysis in <Emphasis Type="Italic">Aconitum</Emphasis> subgen. <Emphasis Type="Italic">Aconitum</Emphasis> reveals excessive rDNA sites in tetraploid taxa

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.     

Molecular cytogenetic characterization of the Amazon River dolphin Inia geoffrensis

Classical and molecular cytogenetic (18S rDNA, telomeric sequence, and LINE-1 retrotransposon probes) studies were carried out to contribute to an understanding of the organization of repeated DNA elements in the Amazon River dolphin (boto, Inia geoffrensis). Twenty-seven specimens were examined, each presenting 2n?=?44 chromosomes, the karyotype formula?12m?+?14sm?+?6st?+?10t?+?XX/XY, and fundamental number (FN)?=?74. C-positive heterochromatin was observed in terminal and interstitial positions, with the occurrence of polymorphism. Interstitial telomeric sequences were not observed. The nucleolar organizer region (NOR) was located at a single site on a smallest autosomal pair. LINE-1 was preferentially distributed in the euchromatin regions, with the greatest accumulation on the X chromosome. Although the karyotype structure in cetaceans is considered to be conserved, the boto karyotype demonstrated significant variations in its formula, heterochromatin distribution, and the location of the NOR compared to other cetacean species. These results contribute to knowledge of the chromosome organization in boto and to a better understanding of karyoevolution in cetaceans.     

中国4种蝙蝠的G-带和C-带

首次报道了中国4种蝙蝠的G-带和C-带核型。大长舌果蝠(Eonycteris spelaea)二倍染色体数目(2n)为36,常染色体臂数(FN)为56;马来假吸血蝠(Megaderma spasma)2n=38,FN=70;黑髯墓蝠(Taphozous melanopogon)2n=42,FN=64;皱唇蝠(Chaerephon plicata)2n=48,FN=54。通过C-带显示,除着丝粒异染色质外,在皱唇蝠的许多染色体臂内和马来假吸血蝠染色体的端粒处也有较多的插入异染色质,大长舌果蝠的基因组中既有臂内异染色质也有端粒异染色质。     

Cytogenetics of Synbranchiformes: a comparative analysis of two Synbranchus Bloch, 1795 species from the Amazon

Synbranchidae belongs to the Synbranchiformes and occurs in Africa, Asia, Australia, Mexico, and Central and South America. This family comprises four genera: Synbranchus, Ophisternon, Monopterus, and Macrotrema. Only two are known from the neotropical region, Ophisternon and Synbranchus. According to current classification, Synbranchus has three valid species: S. marmoratus (Bloch 1795), S. madeirae (Rosen and Rumney 1972), and S. lampreia (Favorito, Zanata and Assump??o 2005). Thus the present research is aimed to cytogenetically characterize (by classical and molecular methods) two syntopic species-S. aff. lampreia and S. madeirae-from the central Amazon basin to validate the taxonomy of both species and provide a revisionary discussion on the cytogenetics of Synbranchiformes. Synbranchus aff. lampreia was found to possess 2n?=?44 chromosomes (6?m?+?2st?+?36a, NF?=?50), while S. madeirae had 2n?=?46 chromosomes (6?m?+?2st?+?38a, NF?=?52). Constitutive heterochromatin was dominant in the centromeric and terminal regions of most of the chromosomes in both species, although the precise distribution patterns were species-specific. The nucleolar organizing region was single in S. aff. lampreia and multiple in S. madeirae, as indicated by both AgNO(3) and hybridization using 18S rDNA probes. The 5S rDNA sites were located interstitially on the long arms of an acrocentric pair in both species, and the telomeric probe did not show any interstitial sites in either species. These data indicate the occurrence of interspecific karyotypic variability in Synbranchus and suggest that taxonomic review for this genus is necessary.     

Intraspecific chromosomal and genetic polymorphism in Brassica napus L. detected by cytogenetic and molecular markers

The application of DNA intercalator 9-aminoacridine allowed us to increase the resolution of chromosome C-banding and DAPI-banding patterns and to investigate chromosomal polymorphism in karyotypes of seven spring and six winter rape varieties. It was shown that the pericentromeric and intercalary C-bands of most of the chromosomes in spring rape were smaller in size and less polymorphic than those of winter rape. More 26S and 5S rDNA sites were found in the winter rape karyotypes than the spring varieties. Separate or colocalized 26S and 5S rDNA sites were revealed on chromosomes 4, 5, 6, 8, 10, 14, 15, 16 and 18. Intervarietal and intravarietal polymorphism of the number and chromosomal localization of rDNA sites were detected. The generalized idiogram of chromosomes of 13 Brassica napus varieties with account of all possibilities of C-banding patterns as well as localization of 26S and 5S rDNA sites were constructed. Polymorphism of the examined molecular and cytogenetic markers as well as the heterozygosis level of FAE1.1 gene controlling erucic acid synthesis in rapeseed was higher in the winter varieties than in the spring ones. The obtained data were in a satisfactory agreement with increased tolerance to environmental stress conditions of winter rape.     

A single species,two basic chromosomal numbers: case of Lygeum spartum (Poaceae)

Abstract

The existence of two chromosome numbers (2n?=?16 and 2n?=?40) in Lygeum spartum is confirmed in the Algerian steppe populations of Oran region. Chromosome counts were established for 11 Algerian populations and three supplementary populations from Italy, Spain and Greece. The karyotypes were characterized by chromosome markers obtained using fluorescence in situ hybridization and fluorochrome bandings. The organization of 5S and 18S-5.8S-26S (35S) rDNA was studied in both cytotypes. Six signals of 35S and 2 signals of 5S were observed in 2n?=?16 population, while 10 signals of 35S and 4 signals of 5S were detected in the population with 2n?=?40. All 35S loci were also strongly marked by chromomycin, but negatively stained by Hoechst, which indicates the presence of GC rich DNA in rDNA regions. The B chromosomes were found in both cytotypes, bearing a 35S locus in 2n?=?16 population. Genome size, determined by cytometry of 10 populations, ranged from 9.27?pg for 2n?=?16 to 26.63?pg for 2n?=?40 populations. The sequencing of plastid and nuclear DNA markers did not reveal major differences among 2n?=?16 and 2n?=?40 populations. However, given the differences between two cytotypes and based on their morphological and cytogenetic characteristics, the 2n?=?16 cytotype merits novel taxonomic treatment.     

Methylated-rich regions and tandem repeat arrays along the chromosome complement of Colpodium versicolor (Stev.) Schmalh

The grass Colpodium versicolor (Stev.) Schmalh is one of six angiosperms with extremely reduced chromosome set 2n?=?2x?=?4. The chromosome complement of this species was studied. The DNA methylation pattern was determined with a specific monoclonal antiboby. 5-Methylcytosine residues are present in different chromosomal sites, with specific occurrence, some methylated bands showing differences between homologous chromosomes. Moreover, a fluorescent in situ hybridisation with telomere repeats and 45S rDNA sequences were performed. Hybridisation signals of telomeric repeats are detectable at the distal ends of the two pair of chromosomes, while 45S rDNA is localised in one chromosomal site, corresponding to the secondary constriction. In addition, 45S rDNA, as well as telomere-associated sequences, results to be 5-methylcytosine-enriched. The results are discussed and compared with those previously obtained in other plant systems 2n?=?4 with the aim to enable a better knowledge of the lengthwise differentiation of this chromosome complement.     

Karyotypic characterization and genomic organization of the 5S rDNA in <Emphasis Type="Italic">Erpetoichthys calabaricus</Emphasis> (Osteichthyes,Polypteridae)

Polypterids are a group of Osteichthyan fish whose evolutionary relationships with closer basal ray-finned and lobe-finned fish have been disputed since their discovery. Very little is known about the evolutive karyology in the whole Polypteriformes group. In order to fill this gap, a cytogenetic analysis of Erpetoichthys calabaricus species was performed, using both classical and molecular techniques. Karyotype structure (2n = 36; FN = 72), chromosome location of telomeric sequences (TTAGGG)n and ribosomal 5S and 18S rRNA genes were examined in twenty specimens of E. calabaricus by using Ag-NOR, classical C-banding, sequential CMA3/4',6-diaminidino-2-phenylindole (DAPI) staining and fluorescent in situ hybridization (FISH). CMA3 marked all centromerical and some (no. 1 and no. 15) telomeric regions. Staining with Ag-NOR and CMA3 showed the presence of two NORs on the p arm of the chromosome pair no. 1. Hybridization with telomeric probes (TTAGGG)n showed signals at the end of all chromosomes. 5S rDNA was cloned and sequenced. After the alignment, the 5S rRNA sequences revealed an organization made up of two different classes of tandem arrays (type I and type II). FISH with 5S rDNA marked the telomeric regions of the small chromosome pair no. 15, while FISH with 18S rDNA marked the telomeric region of the pair no. 1. The results obtained were compared with cariological data on closer species now available in literature.     

Do time, heterochromatin, NORs, or chromosomal rearrangements correlate with distribution of interstitial telomeric repeats in Sigmodon (cotton rats)?

We studied the chromosomal distribution of telomere repeats (TTAGGG)(n) in 8 species of Sigmodon (cotton rats) using chromosome paints fluorescent in situ hybridization (FISH) from Sigmodon hispidus. In 2 species with the proposed primitive karyotype for the genus, telomere repeats were restricted to telomeric sites. But in the other 6 species that include 3 with proposed primitive karyotypes and 3 with highly rearranged karyotypes, telomere repeats were found on both telomeric sites and within interstitial telomeric sites (ITSs). To explain the distribution of ITS in Sigmodon, we gather data from C-bands, silver nitrate staining, G-bands, and chromosomal paint data from previous published studies. We did find some correlation with ITS and heterochromatin, euchromatic chromosomal rearrangements, and nucleolar organizing regions. No one type of chromosomal structure explains all ITS in Sigmodon. Multiple explanations and mechanisms for movement of intragenomic sequences are required to explain ITS in this genus. We rejected the hypothesis that age of a lineage correlates with the presence of ITS using divergence time estimate analyses. This multigene phylogeny places species with ITS (S. arizonae, S. fulviventer, S. hispidus, S. mascotensis, S. ochrognathus, and S. toltecus) in the clade with a species without ITS (S. hirsutus). Lineages with ITS (S. arizonae and S. mascotensis) arose independently from a lineage absent of ITS (S. hirsutus) around 0.67 to 0.83 Ma. The rearranged karyotypes of S. mascotensis and S. arizonae appear to be an independently derived autapomorphic characters, supporting a fast rate of chromosomal changes that vary among species.     

Diversification of a ZZ/ZW sex chromosome system in Characidium fish (Crenuchidae, Characiformes)

Karyotype and other chromosomal markers of Characidium cf. gomesi were analyzed using conventional (Giemsa-staining, Ag-NOR and C-banding) and molecular (Fluorescent in situ hybridization (FISH) with 18S and 5S rDNA biotinylated probes) techniques. Both sexes had invariably diploid chromosome number 2n = 50 while karyotypes of males and females differed. That of male consisted of 32 metacentric + 18 submetacentric chromosomes and that of female consisted 31 metacentric + 18 submetacentric + 1 subtelocentric chromosomes. The Z chromosome was medium-sized metacentric, while W was highly heterochromatinized subtelocentric element. NORs as revealed by Ag-staining were situated at 2–7 telomeric regions while FISH with 18S probes showed consistently 10 signals at telomeric regions. FISH with 5S rDNA probe showed constantly signals at one metacentric pair. Distribution of centromeric heterochromatin was mostly in all chromosome pairs, besides some telomeric sites. The common origin of the sex chromosome system of ZZ/ZW type in the karyotypes of other representatives of the genus analyzed so far might be hypothesized based on biogeography and partial phylogeny of the group.     

Polyploidy, B chromosomes, and heterochromatin characterization of Mimosa caesalpiniifolia Benth. (Fabaceae-Mimosoideae)

Eight populations of Mimosa caesalpiniifolia Benth. were investigated using a cytogenetic approach. Here, we describe for the first time details of the karyotype including chromosome morphology, physical mapping of chromomycin A3 (CMA) 4′,6-diamidino-2-phenylindole (DAPI) and silver staining of nucleolar organizer regions (Ag-NOR banding), as well as 45S rDNA sites. All populations studied showed karyotypes with 2n?=?2x?=?26 small metacentric and submetacentric chromosomes, although some individuals exhibited 2n?=?4x?=?52 chromosomes. Moreover, we observed putative additional B chromosomes in some populations. The CMA banding and fluorescent in situ hybridization techniques revealed NOR heteromorphism on the unique pair containing 45 rDNA site (chromosome 12) while the Ag-NOR banding indicated NORs on both cytotypes. Up to two and four nucleoli were observed, respectively, on individuals with 2n?=?2x?=?26 and 2n?=?4x?=?52 chromosomes and the differences in nucleolar size seems to be directly related to NOR heteromorphism in some individuals. The data present new and important information to understand karyotypic evolution of Mimosa and Fabaceae.     

Chromosome mapping of repetitive sequences in four Serrasalmidae species (Characiformes)

The Serrasalmidae family is composed of a number of commercially interesting species, mainly in the Amazon region where most of these fishes occur. In the present study, we investigated the genomic organization of the 18S and 5S rDNA and telomeric sequences in mitotic chromosomes of four species from the basal clade of the Serrasalmidae family: Colossoma macropomum, Mylossoma aureum, M. duriventre, and Piaractus mesopotamicus, in order to understand the chromosomal evolution in the family. All the species studied had diploid numbers 2n = 54 and exclusively biarmed chromosomes, but variations of the karyotypic formulas were observed. C-banding resulted in similar patterns among the analyzed species, with heterochromatic blocks mainly present in centromeric regions. The 18S rDNA mapping of C. macropomum and P. mesopotamicus revealed multiple sites of this gene; 5S rDNA sites were detected in two chromosome pairs in all species, although not all of them were homeologs. Hybridization with a telomeric probe revealed signals in the terminal portions of chromosomes in all the species and an interstitial signal was observed in one pair of C. macropomum.     

Pericentromeric location of the telomeric DNA sequences on the European grayling chromosomes

The chromosomal characteristics, locations and variations of the C-band positive heterochromatin and telomeric DNA sequences were studied in the European grayling karyotype (Thymallus thymallus, Salmonidae) using conventional C-banding, endonucleases digestion banding, silver nitrate (AgNO₃), chromomycin A₃ and 4′,6-diamidino-2-phenylindole staining techniques as well as fluorescence in situ hybridization (FISH) and primed in situ labelling. Original data on the chromosomal distribution of segments resistant to AluI restriction endonuclease and identification of the C-banded heterochromatin presented here have been used to characterize the grayling karyotype polymorphism. Structural and length polymorphism of the chromosome 21 showing a conspicuous heterochromatin block adjacent to the centromere seems to be the result of the deletion and inversion. Two pairs of nuclear organizer regions (NOR)-bearing chromosomes were found to be polymorphic in size and displaying several distinct forms. FISH with telomeric peptide nucleic acid probe enabled recognition of the conservative telomeric DNA sequences. The karyotype of the thymallid fish is thought to experienced numerous pericentric inversions and internal telomeric sites (ITSs) observed at the pericentromeric regions of the six European grayling metacentric chromosomes are likely relics of the these rearrangements. None of the ITS sites matched either chromosome 21 or NOR bearing chromosomes.     

The Diversity of Karyotypes and Genomes within Section Syllinum of the Genus Linum (Linaceae) Revealed by Molecular Cytogenetic Markers and RAPD Analysis

The wide variation in chromosome number found in species of the genus Linum (2n = 16, 18, 20, 26, 28, 30, 32, 36, 42, 72, 84) indicates that chromosomal mutations have played an important role in the speciation of this taxon. To contribute to a better understanding of the genetic diversity and species relationships in this genus, comparative studies of karyotypes and genomes of species within section Syllinum Griseb. (2n = 26, 28) were carried out. Elongated with 9-aminoacridine chromosomes of 10 species of section Syllinum were investigated by C- and DAPI/С-banding, CMA and Ag-NOR-staining, FISH with probes of rDNA and of telomere repeats. RAPD analysis was also performed. All the chromosome pairs in karyotypes of the studied species were identified. Chromosome DAPI/C-banding patterns of 28-chromosomal species were highly similar. Two of the species differed from the others in chromosomal location of rDNA sites. B chromosomes were revealed in all the 28-chromosomal species. Chromosomes of Linum nodiflorum L. (2n = 26) and the 28-chromosomal species were similar in DAPI/C-banding pattern and localization of several rDNA sites, but they differed in chromosomal size and number. The karyotype of L. nodiflorum was characterized by an intercalary site of telomere repeat, one additional 26S rDNA site and also by the absence of B chromosomes. Structural similarities between different chromosome pairs in karyotypes of the studied species were found indicating their tetraploid origin. RAPD analysis did not distinguish the species except L. nodiflorum. The species of section Syllinum probably originated from a common tetraploid ancestor. The 28-chromosomal species were closely related, but L. nodiflorum diverged significantly from the rest of the species probably due to chromosomal rearrangements occurring during evolution.     

Molecular cytogenetic study of the European bitterling Rhodeus amarus (Teleostei: Cyprinidae: Acheilognathinae)

The European bitterlings (Rhodeus amarus) from the Eastern locations were cytogenetically examined by conventional and molecular techniques. All analyzed individuals presented invariably the same chromosomal constitution of 2n = 48, with 8 metacentrics + 20 submetacentrics + 20 subtelo-acrocentrics and C-banding positive heterochromatin at the pericentromeric regions in most of the chromosomes. Moreover, some of the chromosomes had short arms entirely built with heterochromatin. GC-rich Ag-NORs (nucleolus organizer regions) were located at the short arms of two submetacentric chromosomes, and the length polymorphism of these regions was found. Multiple location of 28S rDNA sequences with fluorescence in situ hybridization signals was observed on the long and/or short arms of three submetacentric chromosomes including NOR regions and short arms of three to five acrocentric chromosomes in the studied fish. 5S rDNA sites were found on the short arms of two subtelocentric chromosomes, and telomeric repeats were localized at the ends of all chromosomes. Provided results have expanded our knowledge concerning genetic characteristics of the European bitterlings that may be profitable in the conservation programs of this endangered species.     

Variation in size and location of the Ag-NOR in the Atlantic halibut (<Emphasis Type="Italic">Hippoglossus hippoglossus</Emphasis>)

The distribution of differentially stained chromatin was studied in the Atlantic halibut (Hippoglossus hippoglossus) chromosomes (2n = 48). Four pairs of homologous chromosomes were identified using a combination of traditional cytogenetic staining techniques (Giemsa/DAPI/CMA3/Ag-NO3). Chromosome 1 showed a length polymorphism (1^S-short, 1^L-long isoforms of the chromosome 1) which was related to the variation of the size of the Ag-NORs. In one specimen the Ag-NOR was translocated from chromosome 1 into the telomeric region on the q-arm of the chromosome 2 forming a derivative chromosome der(2)t(1^S;2)(q?;q?). Four Ag-NOR genotypes have been shown: 1^S1^S, 1^S1^L, 1^L1^L and 1^S der(2)t(1^S;2)(q?;q?). The chromosome rearrangements did not leave any interstitially located telomeric sequences and the telomeres were confined to the ends of the chromosomes. A single chromosomal location of 5S rDNA clusters was found using the PRINS technique. In the extended metaphase spreads two adjacent clusters of 5S rDNA could be seen on one chromosome while condensed chromatin gave a single hybridization signal. Double 5S rDNA signals on the same chromosome arm suggested paracentric inversion of the minor rDNA site. 5S rDNA clusters were not co-localized with Ag-NORs. Although female and male karyotypes were compared no sex related cytogenetic markers were found.     

Cytogenetic analysis in Polypterus ornatipinnis (Actinopterygii, Cladistia, Polypteridae) and 5S rDNA

Polypteridae is a family of archaic freshwater African fish that constitute an interesting subject for the study of the karyological evolution in vertebrates, on account of their primitive morphological characters and peculiar relationships with lower Osteichthyans. In this paper, a cytogenetic analysis on twenty specimens of both sexes of Polypterus ornatipinnis the ornate "bichir", coming from the Congo River basin, was performed by using both classical and molecular techniques. The karyotypic formula (2n=36; FN=72) was composed of 26 M+10 SM. The Alu I banding, performed to characterize heterochromatin in this species, was mainly centromeric. Both the chromosome location of the ribosomal 5S and 18S rRNA genes were examined by using Ag-NOR, classical C-banding, CMA(3) staining and FISH. CMA(3) marked all centromerical regions and showed the presence of two GC rich regions on the p arm of the chromosome pair n°1 and on the q arm of the pair n°14. Staining with Ag-NOR marked the only telomeric region of the chromosome n°1 p arm. After PCR, the 5S rDNA in this species was cloned, sequenced and analyzed. In the 665bp 5S rDNA sequence of P.ornatipinnis, a conserved 120bp gene region for the 5S rDNA was identified, followed by a non-transcribed variable spacer (NTS) which included simple repeats, microsatellites and a fragment of a non-LTR retrotransposon R-TEX. FISH with 5S rDNA marked the subtelomeric region of the q arm of the chromosome pair n°14, previously marked by CMA(3). FISH with 18S rDNA marked the telomeric region of the p arm of the pair n°1, previously marked both by Ag-NOR and CMA(3). The (GATA)(7) repeats marked the telomeric regions of all chromosome pairs, with the exclusion of the n°1, n°3 and n°14; hybridization with telomeric probes (TTAGGG)(n) showed signals at the end of all chromosomes. Karyotype evolution in Polypterus genus was finally discussed, including the new data obtained.     

Archolaemus janeae (Gymnotiformes,Teleostei): First insights into karyotype and repetitive DNA distribution in two populations of the Amazon

Archolaemus, one of the five genera of Neotropical freshwater fish of the family Sternopygidae (Gymnotiformes), was long considered a monotypic genus represented by Archolaemus blax. Currently, it consists of six species, most of them occurring in the Amazon region. There are no cytogenetic data for species of this genus. In the present study, we used classical cytogenetics (conventional staining and C‐banding) and molecular cytogenetics (probes of telomeric sequences and multigenic families 18S rDNA, 5S rDNA, and U2 snDNA) to study the karyotype of Archolaemus janeae from Xingu and Tapajós rivers in the state of Pará (Brazil). The results showed that the two populations have identical karyotypes with 46 chromosomes: four submetacentric and 42 acrocentric (2n = 46; 4m/sm + 42a). Constitutive heterochromatin occurs in the centromeric region of all chromosomes, in addition to small bands in the interstitial and distal regions of some pairs. The 18S rDNA occurs in the distal region of the short arm of pair 2; the 5S rDNA occurs in five chromosome pairs; and the U2 snDNA sequence occurs in chromosome pairs 3, 6, and 13. No interstitial telomeric sequence was observed. These results show karyotypic similarity between the studied populations suggesting the existence of a single species and are of great importance as a reference for future cytotaxonomic studies of the genus.     

Reduction of chromosome number in Eleocharis subarticulata (Cyperaceae) by multiple translocations

Eleocharis subarticulata is recorded as the third species of Cyperaceae with a reduced chromosome number ( n  = 3), following reports on Rhynchospora tenuis ( n  = 2) and Fimbristylis umbellaris ( n  = 3). For Eleocharis, the numbers recorded to date vary from 2 n  = 10 to 2 n  = c. 196, with x  = 5 as the possible basic number. The karyotype of E. subarticulata was studied using conventional staining (mitosis and meiosis), C-CMA₃/DAPI banding, and FISH with 45S rDNA and telomere probes. The chromosomes showed no primary constrictions, as expected in the holocentric chromosomes of Cyperaceae. The meiotic behaviour was abnormal, with a single multivalent ring of six chromosomes at metaphase I, resulting from multiple translocations. At anaphase I six chromatids migrated to each pole, evidencing the inverted meiosis, and these groups were also visible at metaphase II. The C-CMA₃/DAPI banding technique showed only four terminal GC-rich blocks. FISH with 45S rDNA probes revealed four terminal signals, probably associated with GC-rich blocks. The telomeric probe located terminal signals in all the chromosomes, besides a hybridization site in the middle of the large pair. The occurrence of ectopic telomeric sites has not been described previously for plants with holokinetic karyotypes and with reduced chromosome numbers. These data reinforce the hypothesis of the reduction in chromosome number by multiple translocations.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 149 , 457–464.