Nucleolar Constrictions Research Articles

Karyotypic diversification and its contribution to the taxonomy of Eleocharis (Cyperaceae) from Brazil

A karyotype analysis of 147 populations of 25 Brazilian species of Eleocharis (Cyperaceae) was carried out, including representatives of the three subgenera that occur in the country: Limnochloa, Scirpidium and Eleocharis. The analyses showed chromosomes without centromeres, but with terminal nucleolar constrictions (satellites) in some chromosomes. The chromosome numbers varied from 2n = 6 in E. subarticulata and E. maculosa to 2n = 60 in E. laeviglumis, but the chromosome basic number x = 5 was confirmed. Species of the subgenera Eleocharis and Scirpidium possess fewer and larger chromosomes, while those in the subgenus Limnochloa have small and more numerous chromosomes. These features indicate that the karyotypes of the subgenera Eleocharis and Scirpidium are more closely related, in agreement with morphological and phylogenetical data. The representatives of the section Eleocharis exhibited the largest differences in chromosome number and size, probably due to chromosome fission and fusion. Polyploidy was the most common event in this group. Nevertheless, most of the studied species exhibited regular meiosis with only bivalent formation, even the polyploids, such as in E. geniculata and E. sellowiana. The cytogenetic information obtained showed quite variable karyotypes with chromosomes gradually decreasing in size, and predominance of polyploidy. These results are useful in the differentiation of the subgenera.

Giemsa C-banded karyotypes of South American Hordeum (Poaceae): I. 14 diploid taxa

The C-banded karyotypes of the 12 diploid, South American Hordeum taxa, H. stenostachys, H. chilense, H. flexuosum, H. euclaston, H. comosum, H. pubiflorum, H. patagonicum ssp. patagonicum, ssp. setifolium, ssp. santacrucense, ssp. mustersii, and ssp. magellanicum, and H. erectifolium, were similar, with four metacentric, one submetacentric, and two SAT-chromosome pairs, one metacentric pair with long and one submetacentric pair with shorter satellites. The banding patterns normally had between 4 and 12 very small or small bands per chromosome occurring at telomeres and centromeres, at the nucleolar constrictions, and intercalarily with no preferential disposition. Compared to the common karyotype, H. muticum and H. cordobense had corresponding banding patterns, but in H. muticum the metacentric SAT-chromosome pair was replaced by a metacentric pair without satellites, and in H. cordobense it carried small satellites, possibly produced through a paracentric inversion. The overall similarity of the C-banded karyotypes supports the view (i) that the South and North American diploids are closely related; (ii) that they contain the same basic genome (H); and (iii) that the biological relevance of referring the taxa to three sections is questionable. C-banded karyotypes are normally not a good diagnostic character in this material.

Giemsa C-banded karyotypes of South and Central American Hordeum (Poaceae):

The chromosomes of the six South and Central American polyploid Hordeum species, H. procerum (6x). H. lechleri (6x). H. tetraploidum (4x), H. fuegianum (4x). H. parodii (6x), and H. guatemalense (4x). had similar C-banding patterns with normally between two and 12 very small or small bands per chromosome at no preferential positions. Marker chromosome morphology suggested that all taxa contain two genomes similar to those of H. juhatum and H. hrachyantherum (4x); however, in H. tetraploidum. H. fuegianum. and H. parodii they are modified through introgression from H. patagonicum (2x). The karyotypes of the two latter tetraploids are considered homologous although H. fuegianum has an extra SAT-chromosome pair. H. prucerum and H. lechleri are proposed to combine the genomes of H. jubatum or H. brachyan-therum (4x) and the South American H. cordohense (2x) and an unidentified South American diploid Hordeum species, respectively; and H. parodii, the genomes of H. tetraploidum and the South American H. muticum (2x). The karyotype common to H. juhatum, H. brachyantherum (4x). and H. guatemalense is suggested to comprise the genome of the Asian H. roshevitzii (2x) besides that of the North American H. brachyantherum (2x). The proposed origin of the polyploid species indicates that it is hardly biologically relevant to refer them to separate taxonomic sections. One population of H. procerum had a SAT-chromosome pair with active nucleolar constrictions in both arms.

Localization of chemically induced chromosomal aberrations in three different karyotypes of Viciafaba

Andersson, H. C. and Kihlman, B. A. 1987. Localization of chemically induced chromosomal aberrations in three different karyotypes of Vicia faba. — Hereditas 107:15–25. Lund, Sweden. ISSN 0018–0661. Received October 3, 1986 For the purpose of mapping the distribution of chromosomal aberrations. Rieger and Michaelis have divided the chromosomes of Viciafaba into segments, numbered 1–28. We have used this mapping system in a study of the localization of aberrations in segments nos. 2 (=nucleolar constriction) and 4 after treatments of root tips of Vicia faba with mitomycin C (MMC), maleic hydrazide (MH), hydroxyurea (HU) and 8-ethoxy-caffeine (EOC). Seedlings of three different karyotypes were used in these experiments. In all three karyotypes. the chromatid aberrations induced by MMC and MH were preferentially localized in segment 4. whereas a high frequency of those induced by HU and EOC were localized in segment 2. The types of aberration induced by HU and EOC in segment 2 differed. however. After treatments with HU, the aberrations were almost exclusively chromatid interchanges. whereas the majority of the aberrations induced by EOC in segment 2 were isochromatid breaks. Of the exchanges induced by EOC in segment 2, more than 50 were triradials. whereas less than 10 % of the exchanges induced by HU in segment 2 were of the triradial type.

Cytogenetical and cytotaxonomical analysis of some Brazilian species of Eleocharis (Cyperaceae)

Karyotype analysis of 21 samples of 11 species of Eleocharis (Cyperaceae) from 10 localities in Brazil, showed the presence of chromosomes without primary constrictions and parallel movement of chromatids at metaphase–anaphase transition. Only the terminal nucleolar constrictions (satellites) were visualised. The chromosome numbers varied from 2n = 6 in E. subarticulata to 2n = 54 in E. acutangula, but the chromosome basic number x = 5 was confirmed. Generally, C-CMA3+ bands appear mostly in the extremities of the chromosomes, associated to NOR, and interstitial C-CMA3 bands were found only in E. geniculata and E. acutangula. C-DAPI+ bands were not found. Fluorescence in situ hybridisation (FISH) with the 45S rDNA probe was performed in five species. The results showed from four to eight hybridisation signals, always terminal. The analysed species include representatives of the following three subgenera of Eleocharis that occur in Brazil: Limnochloa, Scirpidium and Eleocharis. Species from the subgenus Limnochloa have small and numerous chromosomes. The remaining species, belonging to subgenera Eleocharis and Scirpidium, possess fewer and larger chromosomes. In subgenus Eleocharis, karyotypes of the section Eleocharis were differentiated by symploidy, agmatoploidy and polyploidy, whereas species of the section Eleogenus were all polyploids. Polyploidy seems to be the most frequent event in the karyotype differentiation in Eleocharis, but changes in the chromosome size and repetitive DNA sites were also observed.

Karyotypes of Elymus scabrifolius (Poaceae: Triticeae) from South America studied by banding techniques and in situ hybridization.

Karyotypes of 4 accessions of Elymus scabrifolius (2n = 4x = 28) were investigated by Giemsa C- and N-banding, GAA-banding (one accession), AgNO3-staining and in situ hybridization with the rDNA probe pTa71. Two additional accessions were studied in less detail. The chromosomes were large (9-14 microns). The complements included 11 pairs of metacentrics, one with conspicuous satellites on the short arms, and 3 pairs of submetacentrics. Two of 4 accessions from Eastern Argentina and Uruguay had minute or small satellites on a submetacentric pair. No such satellites were observed in the other two accessions. In two accessions from the Cordoba province, a non-homologous submetacentric pair had very long satellites. AgNO3-staining established the presence of 4 nucleoli, two larger and two small ones, in 5 accessions. The C-banding patterns comprised from one to 12 conspicuous bands per chromosome at no preferential positions. The amount of constitutive heterochromatin (19-21%) was the highest hitherto established in the Triticeae. Similarities in banding patterns and chromosome morphology identified homologous and discriminated between non-homologous chromosomes within and, except for two chromosomes, between plants. Heteromorphic chromosome pairs were identified in satellite-carrying chromosomes only. N-banding produced conspicuous bands overall at the same positions as C-banding. GAA-banding patterns were similar to N-banding patterns. The rDNA probe hybridized to chromosome segments at nucleolar constrictions only. The production of C- and N-banding patterns in both genomes of E. scabrifolius suggests the presence of two H genomes and the absence of the pivotal St genome of Elymus. On account of the uncertain identity of one genome, and the overall similar gross morphology of E. scabrifolius and other tetraploid South American species referred to Elymus, E. scabrifolius is retained in Elymus.

Karyotype evolution and cytotaxonomy in Brazilian species of Rhynchospora Vahl (Cyperaceae)

Karyotypes were analysed in 113 populations of 34 species of Rhynchospora (Cyperaceae). They showed typical holocentric chromosomes lacking primary constrictions. Nucleolar constrictions were observed in the terminal regions of a few chromosomes (except in R. nanuzae, in which they were interstitial). The chromosome numbers varied between 2n =4 and 2 n=50. The primary base number seems to be x=5; x=6 and x=9 are secondary. Dysploidy occurred at low frequency, whereas polyploidy seemed to be the predominant event in the karyotype evolution of the genus. Karyotypic differences were found in R. consanguinea var. speciosa and R. consanguinea var.rigida and the closely related R. emaciata, R. riparia and R. tenuis from sectionTenues . On the other hand, karyotypic similarities occurred among sections Valderugosae, Marisculae,Stenophyllae and Cernuae.

Karyotype evolution and cytotaxonomy in Brazilian species of Rhynchospora Vahl (Cyperaceae)

Abstract Karyotypes were analysed in 113 populations of 34 species of Rhynchospora (Cyperaceae). They showed typical holocentric chromosomes lacking primary constrictions. Nucleolar constrictions were observed in the terminal regions of a few chromosomes (except in R. nanuzae , in which they were interstitial). The chromosome numbers varied between 2 n =4 and 2 n =50. The primary base number seems to be x=5; x=6 and x=9 are secondary. Dysploidy occurred at low frequency, whereas polyploidy seemed to be the predominant event in the karyotype evolution of the genus. Karyotypic differences were found in R. consanguinea var. speciosa and R. consanguinea var. rigida and the closely related R. emaciata , R. riparia and R. tenuis from section Tenues . On the other hand, karyotypic similarities occurred among sections Valderugosae , Marisculae , Stenophyllae and Cernuae .

Interchromosomal, intercellular and interindividual variability of NORs studied with silver staining and in situ hybridization.

We investigated the relationship between transcriptional activity and the quantity of ribosomal cistrons of the nucleolar organizing regions (NORs) in chromosomal pair 3 of the Spanish mole Talpa occidentalis. Transcriptional activity was estimated by the size of conventional silver-staining signals. The number of ribosomal cistrons was estimated by the size of the in situ hybridization signals obtained with a ribosomal DNA probe. A sample of cells was studied with each method in four different individuals, and the results obtained with the two techniques were compared. Furthermore, sequential analysis on the same cells was carried out to study the association of interstitial nucleolar constrictions with silver staining and in situ hybridization. Interchromosomal, intercellular and interindividual variability were found with both silver staining and in situ hybridization methods. Our results show that transcriptional activity of NORs does not depend exclusively on the number of ribosomal cistrons they have as a high percentage of cells had two NORs with abundant ribosomal cistrons, only one of which was active. Additional factors, probably responsible for the activation of transcription, may be involved in this variability.

Chromosome banding and genome size differentiation inProspero (Hyacinthaceae): Diploids

Prospero is a Mediterranean autumn-flowering genus ofHyacinthaceae commonly classified inScilla asS. autumnalis andS. obtusifolia. Extensive dysploid and polyploid variation has been reported. In the present study 77 diploid accessions from the western to the eastern part of the area of distribution, the major part being from continental Greece and Crete, have been analysed for karyotype structure and, in part, for genome size. Methods employed were acetocarmine staining, Giemsa C-banding, fluorochrome staining mainly with chromomycin A3/DAPI, silver impregnation, and Feulgen densitometry. Banded idiograms were established with a computer assisted karyotype analysis procedure. Chromosome numbers were 2n = 8 inP. obtusifolium, and 2n = 12 and 14 inP. autumnale s. l. Dispensable euchromatic chromosome segments and different types of B chromosomes occurred. Among the cytotypes with 2n = 14 two karyotypes from Turkey differed from each other and from the rest in form, position of the nucleolar constriction, and in genome size. The remaining accessions were similar in karyotype shape but three levels of genome size could be discerned, the highest (1C = 7.50 pg) being found on the Iberian Peninsula, an intermediate one on Corsica and Malta, and the lowest (4.27 pg) in the Aegean. The karyotype with 2n = 12 had an intermediate genome size, and that ofP. obtusifolium a relatively low one. Heterochromatin amount was generally low, but some karyotypes showed characteristic banding patterns. The relationship between the chromosome complements with 2n = 14, 12 and 8 is discussed on the basis of idiograms and DNA amounts.

Physical localization of active and inactive rRNA gene loci in Hordeum marinum spp. gussoneanum (4x) by in situ hybridization

Two populations of the diploid and 10 populations of the tetraploid cytotype of Hordeum marinum ssp. gussoneanum were studied for the presence of chromosomal segments harbouring rDNA. Conventional cytological methods established the presence of only one satellited (SAT) chromosome pair in both cytotypes. This was supported by silver staining revealing two NORs and two standard-sized nucleoli. Two additional micronucleoli were observed in a few interphases of two tetraploid populations indicating the presence of an extra chromosome pair with very low nucleolus-forming activity. In situ hybridization with the wheat rDNA probe pTA71 identified intense signals at the nucleolar constrictions of the SAT chromosomes of both cytotypes and weaker signals in a chromosome pair of the tetraploid cytotype, morphologically similar to the SAT chromosomes but without visible nucleolar constrictions. This confirms the presence of rDNA in two chromosome pairs in the tetraploid cytotype. The morphological similarity between these two pairs and the SAT-chromosome pair of the diploid cytotype as well as an identical position of the signals in all three pairs give additional support to an autoploid origin of the tetraploid cytotype. The rDNA at the nucleolar constrictions consisted of two segments of condensed rDNA of different sizes connected by diffuse rDNA. The rDNA of the chromosome pair without nucleolar constrictions was condensed supporting that this conformation is connected with inactivity. The tripartite structure of the rDNA at the nucleolar constrictions corresponds to similar tripartite structures observed after silver staining and Giemsa C-banding.Key words: in situ hybridization, rDNA location, Hordeum marinum, autoploidy, inactive NORs.

Cold-sensitive chromosome regions and their relation to constitutive heterochromatin in Cestrum parqui (Solanaceae)

The structural cause for cold-induced undercondensation of certain chromosome segments is still unknown, and no consistent cytochemical correlations have emerged as yet. Cestrum parqui belongs to one of the few plant genera having chromosomes with such cold-sensitive regions. In the present study, four heterochromatin classes were distinguished in the karyotype of this species by sequential fluorochrome staining with chromomycin A3, DAPI, and D 287/170, and C-banding, N-banding, and silver impregnation. (i) Cold-sensitive regions (CSRs): Banding behaviour indicates AT-rich constitutive heterochromatin. Silver impregnation occurs after cold-treatment from interphase to metaphase. CSRs are subject to polymorphisms. Quantitatively they are only a minor component of the band endowment. (ii) Nucleolar organizers: Two pairs were identified. Banding behaviour indicates GC-rich constitutive heterochromatin. The nucleolar constrictions proper are morphologically indistinct at mitotic metaphase and lose silver impregnation capability at that stage. (iii) Non-nucleolar CMA-positively fluorescent C-bands: There is only one polymorphic paracentromeric band in this class, (iv) Low-fluorescence N-bands. These show quenched fluorescence with all fluorochromes and occur as clusters of small bands scattered over all chromosome arms. This class of bands is quantitatively predominating. Dull fluorescence with both the "GC-specific" chromomycin and the "AT-specific" DAPI is an anomaly but not completely unknown in plants.Key words: Cestrum parqui, cold-sensitive regions, heterochromatin, chromosome banding, silver impregnation.

Structural differentiation of the nucleolus-organizing regions between mitotic and epidermal cells inVicia faba

SUMMARYThe nucleolar secondary constrictions of Vicia faba chromosomes were filled with a weakly stained substance when the sections were treated with conventional double staining and examined under an electron microscope. But both silver staining and ribonucleoprotein preferential staining contrasted these constrictions as positively stained areas. On the other hand, the nucleolus-associated chromatin blocks in the epidermal cells were clearly impregnated with silver although they were fully condensed, suggesting that ribosomal (r) RNA genes are organized into the condensed chromosomal segment when cells differentiate into specialized cells such as the epidermal cells.

Giemsa C-banded karyotypes of Hordeum marinum and H. murinum

Giemsa C-banding patterns of the predominantly self-pollinating, annual species Hordeum marinum (2x, 4x) and H. murinum (2x, 4x, 6x) showed mostly very small to small bands at centromeric and telomeric positions, at one or both sides of the nucleolar constrictions, and at intercalary positions with no preferential disposition. A similar distribution of bands has been observed in other Hordeum species, suggesting that the pattern is the basic one in the genus Hordeum. Hordeum murinum, especially the hexaploid cytotype, was distinguished from H. marinum by having more numerous and more conspicuous bands, resulting in a significantly higher percentage of constitutive heterochromatin (9–17 vs. 4–8%). The differences in C-banding patterns supported by differences in chromosome morphology confirm that H. marinum and H. murinum are not closely related. Banding-pattern polymorphism was prevalent among populations but unobserved within populations. In spite of this polymorphism, banding patterns in combination with chromosome morphology identified homologous chromosomes of different populations of a taxon and indicated that the chromosome complements of the polyploids of both species comprised the genome of the related diploid as well as one or two "unidentified" genomes. This agrees with an alloploid origin of polyploids. The C-banding patterns of H. marinum ssp. marinum and H. marinum ssp. gussoneanum (2x) showed some divergence in spite of the close relationship. The C-banded karyotypes of H. murinum ssp. murinum and H. murinum ssp. leporinum (4x) were very similar, supporting conspecificity. Chromosome lengths and longest/shortest chromosome ratios were fairly similar to those previously published, supporting the conclusion that linear relationships of chromosomes are normally stable within genomes. The taxonomy of the two species is discussed.Key words: C-banding, karyotypes, Hordeum.

The Basic Karyotype of Lotus tenuis C-banding and Feulgen Studies

The basic karyotype of L. tenuis is illustrated. The study of Feulgen stained metaphases has shown that the chromosome complement consists of four pairs of median chromosomes and two pairs of submedian chromosomes. Two nucleolar constrictions characterize the first homologous pair. The C-banding pattern includes large pericentric bands in each chromosome pair and a terminal band in the short arm of chromosome 3

Ribosomal RNA genes in B chromosomes of Crepis capillaris detected by non-radioactive in situ hybridization.

A non-radioactive in situ hybridization method using biotin-labelled rDNA has made it possible to localize rRNA genes not only at the secondary constriction in both homologous chromosomes No. 3 of Crepis capillaris but also in the B chromosomes occurring in the plants employed. Very clear dot-like rDNA signals at the telomeres of both arms were observed in all B chromosomes. Histochemical silver staining, which is indicative of transcriptional activity of rRNA gene clusters, resulted in both darkly-staining nucleolar constrictions of chromosomes No. 3 and silver deposits at the telomeres of Bs. We conclude that the B chromosomes of C. capillaris are isochromosomes with active rRNA genes located near both telomeres.

Spontaneous chromosomal rearrangements in cultivated and wild barleys

Four of 1,240 cultivated barley lines collected from different regions of the world and 3 of 120 lines of wild barley, Hordeum spontaneum C. Koch, carry spontaneous reciprocal translocations. Break-point positions and rearrangements in the interchanged chromosomes have been examined by both test crosses and Giemsa banding techniques. The four translocation lines in cultivated barley were all of Ethiopian origin and have the same translocation involving chromosomes 2 and 4. The breakpoints are at the centromeres of both chromosomes, resulting in interchanged chromosomes 2S+4S and 2L+4L (S=short arm, L=long arm). A wild barley line, Spont.II, also has translocated chromosomes 2 and 4 which are broken at the centromeres. The resultant chromosomes are, however, 2S+4L and 2L+4S. Another wild barley line, Spont.S-4, has interchanged chromosomes with breakpoints in the short arm of chromosome 3 and the long arm of chromosome 7. In addition, this line has a paracentric inversion in the short arm of chromosome 7 that includes a part of nucleolar constriction, resulting in two tandemly arranged nucleolar constrictions. The third wild barley line, Spont.S-7, has interchanged chromosomes with breakpoints in the long arms of both chromosomes 3 and 6. The translocated chromosome 3 is metacentric and the translocated chromosome 6 has a long arm similar in length to the long arm of chromosome 7.

Comparative cytogenetics of the primitive frog, <i>Leiopelma archeyi </i>(Anura, Leiopelmatidae)

Chromosomally, <i>Leiopelma archeyi </i>is extremely similar to <i>L</i>. <i>hamiltoni, </i>a closely related species. Both have 2n = 18 chromosomes. Contrary to a previous report, the nucleolar organizer region and secondary constriction in <i>L</i>. <i>archeyi </i>are near the telomere of the smallest, telocentric chromosome, as in <i>L</i>. <i>hamiltoni</i>. The arm-length ratios of all chromosomes are virtually identical in the two species, expect for chromosomes 2 and 3, which show evidence of a past translocation. However, <i>L</i>. <i>archeyi </i>has much less heterochromatin than does <i>L</i>. <i>hamiltoni, </i>and, unlike <i>L</i>. <i>hamiltoni, </i>heteromorphic sex chromosomes are not discernable. These frogs demonstrate two stages in the evolution of sex-chromosome differentiation related to the extent of heterochromatin accumulation.

GIEMSA C‐BANDED KARYOTYPES OF SEVEN NORTH AMERICAN SPECIES OF ALLIUM

The karyotypes of seven North American Allium species were studied by Giemsa C‐banding technique. Two species (A. shoenoprasum and A. tricoccum) were diploids with 2n = 16 chromosomes. Three species (A. cernuum, A. douglasii and A. geyeri) were also diploids but with 2n = 14 chromsomes. Diploid and tetraploid populations of A. textile (2n = 14, 28) were studied. The population of A. canadense studied here was a tetraploid (2n = 28). All these North American species, except A. geyeri, possessed centromeric bands in all their chromosomes and nucleolar constriction bands in their satellited chromosomes. Allium shoenoprasum contained telomeric bands in most of its chromosomes but the other species had them only in a small number of chromsomes. Only three species (A. shoenoprasum, A. textile and A. tricoccum) were found to have intercalary bands in some chromosomes. The heterochromatin distribution in B chromosomes of three species was also observed. In A. cernuum, the heterochromatin occupied most of the length of all its Bs, but in A. shoenoprasum, heterochromatin was concentrated in the centromeric region. One population of A. textile (CC1179) was found to have a B chromosome in which very little heterochromatin existed.

Localisation of NORs and counterstain-enhanced fluorescence studies in Salmo gairdneri and Salmo trutta (Pisces, Salmonidae)

The karyotypes of the rainbow trout (Salmo gairdneri R.) and the brown trout (Salmo trutta L.) were analyzed by means of silver staining and the chromomycin A3/distamycin A/DAPI fluorescence banding technique. The nucleolus organizer regions (NORs) were localized at the secondary constrictions of chromosome no. 14 in S. gairdneri and of chromosome no. 10 in S. trutta. Additional silver positive dots were observed at or close to several centromeres in S. gairdneri. Brilliant chromomycin A3 (CMA3) fluorescence heterochromatin blocks were localized on both sides of the nucleolar constrictions in S. gairdneri. A polymorphic CMA3 positive band was detected close to the NORs of S. trutta. No distamycin A/DAPI intense heterochromatin blocks were detected in the genomes of the two Salmo species investigated.