Pair Of SAT-chromosomes Research Articles

Advances in the cytogenetics of Annonaceae, the case of Annona cherimola L.

Annonaceae represent the largest extant family among the early divergent angiosperms. Despite the long-standing interest in its evolutionary and taxonomic aspects, cytogenetic studies on this family remain extremely few even on economically important species. With this study, we realized a detailed characterization of the chromosomes of Annona cherimola (2n = 14) by a combination of in situ hybridization techniques, fluorochrome banding, and karyomorphological analysis. FISH revealed that 45S and 5S rDNA sites are co-localized in correspondence to the secondary constrictions of the SAT-chromosome pair. Some hypotheses on the organization of the linked 45S and 5S rDNA repeats have been made. FISH with Arabidopsis-type telomeric arrays demonstrated that the A. cherimola telomeres are constituted by TTTAGGG sequences and that they are exclusively localized at the extremities of chromosomes. An insight into the chromosome structure of A. cherimola was obtained by the self-GISH procedure which revealed highly repeated DNA sequences localized in the centromeric regions of all chromosomes. The correspondence of s-GISH signals with DAPI banding suggests that these sequences are the principal component of the centromeric heterochromatin of this species. The karyotype of A. cherimola here described is proposed as the basic reference karyotype for successive investigations in Annonaceae.

Karyotypes, heterochromatin distribution and rDNA patterns in South American Grindelia (Asteraceae)

Grindelia is a genus with a complex evolutionary history with reticulate evolution. We studied the karyotype, fluorescent banding, and fluorescence in situ hybridization (FISH) using 18–5.8–26 S and 5 S ribosomal DNA probes to survey karyotypic diversity of South American Grindelia species. Chromosome basic numbers were x = 6 (with several ploidy levels: 2x, 4x, and 6x). All the Grindelia studied conserved the patterns of CG-rich heterochromatin and 18-5.8-26 S rDNA. The third m sat-chromosome pair was homeologous in Grindelia. Chromosome variation, although not always large, accompanied the evolutionary divergence of the taxa studied. The Grindelia studied formed two species groups: (1) G. globularifolia and G. pulchella var. pulchella, (2) G. buphthalmoides, G. cabrerae var. alatocarpa and var. cabrerae, G. chiloensis, G. orientalis, and G. prostrata. These groups do not show any morphological affinities and their phylogenetic relationships are not clearly resolved, suggesting that these groups have recently diverged.

Karyotype analysis in Chaerophyllum cicutaria Vill. with special emphasis on satellited chromosomes

Karyological studies were carried out on plants of <em>Chaerophyllum cicutaria (Umbelliferae)</em>, which came from both lowland and montane natural populations. The chromosome number in all the examined plants was 2n = 22 and their karyotypes, though similar in general, showed some minute but distinct differences. There was` a single pair of SAT chromosomes in the chromosome complement. They had compound satellites divided into two or three segments. Seven morphological types of SAT chromosomes differing in number and size of satellite segments were distinguished. With respect to SAT chromosome morphology, the species showed both intra- and interpopulational karyological variation.

Methodology Molecular cytogenetic characterization of the Aegilops biuncialis karyotype

Aegilops biuncialis can be hybridized with wheat (Triticum spp) and has been used for wheat breeding and genetic studies. The A. biuncialis karyotype (U(b) U(b) M(b) M(b)) was investigated based on three A. biuncialis accessions grown in China. Two pairs of SAT chromosomes were identified as 1U(b) and 5U(b), with a karyotype formula of 2n = 4x = 28 = 14m + 10sm + 4st. Fluorescence in situ hybridization (FISH) and C-banding approaches were used to analyze the A. biuncialis accession chromosomes at the mitotic stage. Based on the C-banding and FISH patterns, all U(b) and M(b) chromosomes could be discriminated simultaneously; the three A. biuncialis accessions exhibited similar patterns, suggesting a common origin. The U(b) genome from A. biuncialis resembled the U genome in the diploid species A. umbellulata, and it may be related to the tetraploid species containing the U genome. The M(b) genome had some differences compared to the M genome in the diploid species A. comosa, and it may be related to the tetraploid species possessing the M genome. A generalized ideogram was proposed for the A. biuncialis genome, which could be useful for standardized and accurate identification of the A. biuncialis karyotype and chromosomes.

Chromosomal characterization in native populations of Elymus scabrifolius from Argentina through classical and molecular cytogenetics (FISH–GISH)

The karyotype of Elymus scabrifolius (Döll) J.H. Hunz. (2n = 4x = 28) was investigated by DAPI staining and in situ hybridization. All the accessions studied presented a symmetric and uniform karyotype constituted by 9m+2m-sm+3sm. DAPI stain showed 1-7 conspicuous bands in all the chromosomes and polymorphisms between accessions. FISH experiments carried out with 45S rDNA as probe (pTa71) showed strong hybridization signals on the metacentric SAT-chromosome pair 8; the submetacentric SAT-chromosome pair 13 presented weaker hybridization. FISH using pSc119.2 clone as probe identified five chromosome pairs. Then, the combination of chromosome morphology, DAPI-staining, and FISH enabled the accurate identification of each chromosome pair in E. scabrifolius. Genomic in situ hybridization (GISH) experiments using Hordeum DNA as probe on mitotic metaphases confirmed unequivocally the presence of the H genome in E.scabrifolius, allowing us to observe six uniformly labeled chromosome pairs and two chromosome pairs with only one arm labeled. The remaining six chromosome pairs were weakly labeled. The rehybridization of FISH slides with Hordeum DNA as probe allow us to assign the genomic provenance of most of the chromosomes in the studied accessions. Moreover, intergenomic rearrangement was detected between genome H and the still unknown progenitor genome.

Connection between rod bivalents and incomplete meiotic association at NORs in Hordeum marinum Huds.

The hypothesis of a connection between rod bivalent formation and incomplete meiotic association at NORs of SAT-chromosomes of H. marinum is supported. PMCs of H. marinum ssp. gussoneanum (2x), two diploid ssp. marinum × ssp. gussoneanum (2x) hybrids and two ssp. gussoneanum (4x) × Secale cereale hybrids at metaphase I (M-I) were analyzed by in situ hybridization. The probe pTa71 labelled rDNA sites at NORs of a single pair of homologous or near-homologous SAT-chromosomes of H. marinum in each material. In the three diploids, M-I was regular with ring bivalents and one or a few rods (av.13.52 bound arms cell(-1)). More rod bivalents than the expected one out of seven, i.e. 30, 67 and 89% included rDNA-carrying chromosomes. Corresponding bound short arm frequencies were 0.89, 0.72 and 0.52, while long arms and arms of other chromosomes presented complete or near- complete association. The two heterogenomic hybrids had a less regular M-I (av. 8.04 bound arms cell(-1)) including 20% rDNA-carrying rods with bound arm frequencies of 0.29 in short and 0.87 in long arms. Positions of chromosome associations were established in all 150 rDNA-carrying bivalents. In 77 bivalents with short arm associations, 4% of these occurred proximally to, none at, and 96% distally to rDNA sites, i.e. in satellites. In 143 bivalents with long arm associations, 83% occurred at interstitial and 17% at terminal positions. The observations combine increased frequency of rDNA-carrying rods with decreased frequency of association at NOR regions of SAT-chromosomes. The basis for the relationship is discussed.

Meiotic chromosome behaviour and karyomorphology of Aloe vera (L.) Burm. f.

Aloe vera (L.) Burm. f. (the family Aloaceae) indigenous to Africa is an admired medicinal plant used as a folk medicine. Meiotic division was investigated in A. vera with a view to decipher the behavior of chromosomes during prophase I and the subsequent stages of meiosis following acetocarmine squash technique. The various meiotic stages from leptotene to pollen development were studied. Seven bivalents were clearly visible at diplotene, and the chiasma frequency averaged to 1.86 per bivalent and 13.1 per pollen mother cell (PMC). Prophase I stages are difficult to identify due to clumping of chromosome threads. Second nuclear division, however, allows clear distinction of chromosome configuration. Besides clumping, various other types of chromosomal aberrations such as stickiness and fragments at metaphase I, precocious movement of chromosomes, bridges, laggards and unequal separation of chromosomes at anaphase I and unequal separation of chromosomes at telophase II were noted. Karyomorphological study on the other hand, was carried out in anther wall (mitotic) cells of A. vera. Mitotic as well as meiotic studies in the species showed 2n=14 chromosomes including two pairs of sat-chromosomes. The karyotype of the species was adjudged to be typically asymmetric.

Cytological investigations in poly-gamo-dioecious tree Simarouba glauca DC

In angiosperms sexual dimorphism is proved to be an evolutionary advancement and plays a major role in crop improvement in general and in tree species in particular. Identification of sex in absence of morphological markers is a difficult task in such plants. Sex determination in all dioecious plants does not follow a common mechanism. In present investigation an attempt is made to understand the mechanism of sex determination in poly-gamo-dioecious tree species Simarouba glauca DC., an important oil yielding and medicinal plant. Scoring of morphological characters in male and female S. glauca reveals that both are morphologically identical with 2n = 30 chromosomes and exhibit symmetric karyotype and with homomorphic median chromosomes with one pair of SAT chromosomes, but female plant possess chromosomes which are longer than male counterpart and the largest chromosome is more than two fold longer than the smallest.

Karyomorphological studies in Mucuna of India

Mucuna Adans. is a large genus with more than 150 species of annual and perennial legumes of pantropical distribution. Despite considerable economic importance of some of its species, almost no work has been done on their cytogenetic characterization in any part of World. In this paper, we have presented a first report on karyomorphological analysis in four Indian species viz., Mucuna atropurpurea, Mucuna monosperma, Mucuna nigricans and Mucuna pruriens bringing out diploid number for M. atropurpurea and karyotypic formula for all the four species. Root tips were treated with 0.002 M 8-hydroxyquinoline and temporary preparations were made after squash in aceto-carmine. Karyomorphological description for each of the species has been detailed taking into account the following features: chromosome number, total length and relative length, arm ratio of each chromosome, haploid set length and degree of asymmetry. Mitotic metaphases in all the species showed 2n=22 chromosomes. Mucuna nigricans showed two pairs of sat-chromosomes. None of the species, however, revealed identical karyotypic formula indicating occurrence of rearrangements. The haploid set length of annual M. pruriens was found to be reduced in size when compared to perennial species pointing its evolution from the latter.

Physical mapping of rDNA and heterochromatin in chromosomes of 16 Coffea species: A revised view of species differentiation

The chromosome organization among 15 wild diploid Coffea species and cultivated tetraploid C. arabica was determined by fluorochrome banding (CMA, DAPI) and double fluorescence in-situ hybridization (FISH) of 5S and 18S rDNA achieved on the same chromosome plates. Two to five chromosome pairs (plus one putative chromosome B) are marked. Overall, there are two SAT-chromosome pairs for East African species and one for the Malagasy and the West and Central African species. 18S rDNA loci are telomeric and strongly marked the SAT-chromosome pairs. Generally, only one pericentromeric 5S rDNA locus characterized East African species, while an additional minor locus co-localized with the 18S rDNA-SAT locus for the Malagasy species and West and Central African species. A combination of rDNA FISH plus CMA and DAPI banding patterns enables identification of almost all the species, even those for which the genetic or botanical status is still being discussed. C. arabica clearly appears to be an allotetraploid species, including one genome from East Africa and one from West and Central Africa. However, since the minor 5S rDNA-SAT locus present in West/Central African genomes is not detected, two evolutionary hypotheses could be put forward for C. arabica. Considering only the diploid species, global trends are obvious in rDNA signal patterns, genome size variations, and geographic distribution of the species, but there are no clear evolutionary trends. However, complex interactions between these factors and environmental growing conditions exist, which have resulted in loss and gain of rDNA loci and probably also in copy repeat number variations in each rDNA family.

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.

Giemsa C-banded karyotypes of three subspecies of Taeniatherum caput-medusae and of two intergeneric hybrids with Psathyrostachys spp. (Poaceae)

Three subspecies of Taeniatherum caput-medusae (2n=2x=14) had the same karyotype with five pairs of metacentrics, one pair of submetacentrics, and one pair of metacentric SAT-chromosomes with small satellites. The rather similar C-banded karyotypes were characterized by banding patterns with a limited number of mostly small or very small bands randomly distributed. Plants of the same population had identical banding patterns. Banding pattern polymorphism was prevalent, but apparently no larger among than within taxa. The similarity of the C-banded karyotypes supports a close relationship of taxa. Differences in chromosome size and C-banding patterns identified parental genomes in two Taeniatherum×Psathyrostachys hybrids. Psathyrostachys SAT-chromosomes exerted nucleolar dominance. A hierarchy of nucleolar dominance: Hordeum vulgare > P. fragilis > T. caput-medusae is indicated.

Giemsa C-banding in two polyploid, South American Hordeum species, H. tetraploidum and H. lechleri, and their aneuploid hybrids with H. vulgare

The karyotype of H. tetraploidum (2n=4x=28) had eight metacentric, three submetacentric, and three SAT-chromosome pairs. The karyotype of H. lechleri studied in a polyhaploid (2n=3x=21) had thirteen metacentrics, three submetacentrics, and five SAT-chromosomes, one more SAT-chromosome than previously reported, The C-banding patterns of both species were rather similar, having small to larger bands with no preferential disposition. The two species are referred to sections Stenostachys and Critesion, respectively, but similarities among C-banded karyotypes of the two species and some North American taxa of the same sections suggest a rather close relationship and support that the biological basis for their classification with different sections is questionable. C-banding patterns identified the chromosomes of parental genomes in interspecific hybrids between the two species and H. vulgare. The hybrids were stably aneuploid. Both had lost and acquired H. vulgare chromosomes. Thus, somatic elimination of chromosomes was combined with multiplication of chromosomes. The observations of stably aneuploid hybrids have implications for the exploitation of alien germplasm. The activity of non-H. vulgare SAT-chromosomes was partly suppressed in the hybrids, indicating incomplete differential amphiplasty.

Physical mapping of 45S rDNA to metaphase chromosomes in 30 taxonomically diverse plant species

SummaryThe genomic distribution of ribosomal RNA genes (rDNA) has been determined by fluorescence in situ hybridisation (FISH) in 30 diverse plant species, using 45S rDNA as a probe. In most species, physical mapping of 45S rDNA to metaphase chromosomes is reported for the first time. These species could be divided into four groups based on differences in the number and positions of their rDNA loci. Fluorescent signals lay in secondary constrictions and satellites of satellite-chromosomes (SAT-chromosomes) in 14 of the 30 species, including Berberis thunbergii, Plantago major, Sanicula lamelligera, Ficus carica and Robinia pseudoacacia. In another seven species, including Robinia hispida, Kolkwitzia amabilis, Litchi chinensis, Catalpa speciosa and Acer buergerianum, FISH markers were also detected in the terminal and/or peri-centromeric regions of some chromosomes beside secondary constrictions and satellites. There was only one species (Viburnum sargentii) in which four pairs of SAT-chromosomes were found, only one pair of which gave FISH signals. In the other eight species, including Kerria japonica f. pleniflora, Salvia miltiorrhiza, Cucumis sativus and Ulmus pumila, no visible satellites existed and the positions of 45S rDNA loci on the chromosomes were terminal or peri-centromeric. Our results indicate that 45S rDNA can be used to identify individual chromosomes. The polymorphism of 45S rDNA loci is also discussed in this paper.

The Giemsa C-banded Karyotype of Crithopsis Delileana (Poaceae; Triticeae)

Three populations of Crithopsis delileunu had similar karyotypes. They included 14 large chromosomes; five pairs of metacentrics, one pair of submetacentrics, and one pair of metacentric SAT-chromosomes with rather small satellites. The karyotypes of two populations were investigated in detail through application of Giemsa C-banding, Giemsa N-banding and AgN0,-staining to meta- and interphases. The C-banding patterns included a few small to very small, mainly centromeric or telomeric bands. The chromosomes of the two populations were differentiated by banding pattern polymorphism. Banding patterns identified homologous and discriminated among non-homologous chromosomes within the same population. The scarcity of diagnostic bands prevented identification of homologous chromosomes between populations beyond the level obtained from morphology, i.e., of submetdcentrics and SAT chromosomes. N-banding produced no or few weak bands. Silver nitrate staining produced two NORs and two nucleoli corresponding to the number of SAT-chromosomes. The data give some support to a hypothesis of a closer relationship between the genera Critlzopsis and Tueniutherum, than between either of these and the genera Psuthyrostuchys and Hordeum.

Rediscovery of a diploid cytotype of Dasypyrum breviaristatum in Morocco

The chromosome numbers of a total of 273 Dasypyrumbreviaristatum plants sampled from 20 Moroccan and one Greek naturalpopulations were examined. 270 plants from all of the populations weretetraploids. Among them, 223 were eu-tetraploids with 28 chromosomes and 47 wereaneuploids with 25, 27 and 29 chromosomes. Besides, three plants were found tobe diploids among 16 plants from a population in the Moyen Atlas Mountains ofMorocco. This is the second report of a diploid cytotype ofD. breviaristatum since the firstcommunication in 1957. Morphologically, the diploids were similar to but smallerthan the tetraploids in plant height, spike length, spikelet number and leafepidermis cell size. However, it was not possible to distinguish between the twocytotypes based on those morphological characteristics alone. A distinctdifference was found between the two cytotypes only in the number of trichomeson the leaf surfaces. The karyotype of the diploid cytotype consisted of a pairof SAT-chromosomes, five pairs of metacentric and a pair of submetacentricchromosomes. Based on the similarity in karyotype and in plant morphologybetween the two cytotypes of D.breviaristatum, we suggest that the diploid cytotype is themost probable candidate for the ancestral form of the tetraploid cytotype.

Karyotype and Nuclear DNA Content of Six Species of Astragalus (Leguminosae).

Karyological characteristics of six Argentinian Astragalus species are reported: A. crucksh-anksii (2n=28), A. illinii (2n=28), A. neuquenensis (2n=28), A. moyanoi (2n=28), A. pehuenches (2n=22) and A. palenae var. grandiflora (2n=26). The x=13 and 14 species have bimodal complements but differ in chromosome morphology and asymmetry indices. All species have a single pair of chromosomes with satellites located on the long arms. A. pehuenches (2n=22, x=11) has a more symmetrical karyotype and a pair of SAT chromosomes with a satellite located on the short arms. Among the species with 2n=28, A. moyanoi has significantly greater DNA content than the rest. The species with the lowest chromosome number, A. pehuenches, has the highest DNA content. The members of species with 2n=28 studied in the present work are similar in both vegetative and reproductive morphology.

Comparison of the Giemsa C-banded karyotypes of the three subspecies ofPsathyrostachys fragilis, subspp.villosus (2x),secaliformis (2x, 4x), andfragilis (2x) (Poaceae), with notes on chromosome pairing

The karyotypes of diploidP. fragilis subsp.villosus (2n = 2x = 14) and tetraploid subsp.secaliformis (2n = 4x = 28) were studied by Giemsa C- and N-banding, and AgNO3 staining and compared with the karyotype of subsp.fragilis (2x). The complements of subsp.villosus and subsp.fragilis were similar, with 8 metacentric and 6 SAT-chromosomes, one metacentric and two submetacentric pairs, with small to minute, polymorphic, heterochromatic satellites. The complement of subsp.secaliformis on the whole agreed with a doubling of the complement of diploidP. fragilis, suggesting autopolyploidy. Only the presence of 12 nucleoli in interphases identified 6 SAT-chromosome pairs. In subsp.villosus one or two extra micronucleoli indicated a chromosome pair with very low nucleolusforming activity, bringing the number of SAT-chromosome pairs to 4. This number may be a characteristc ofPsathyrostachys. Besides very small, inconsistently observed bands, the C-banding pattern consisted of 0–3 small bands per chromosome at intercalary and terminal locations, and at NORs. The level of banding pattern polymorphism was low, but enough to indicate that the taxa are outbreeders. Similarities in chromosome morphology and C-banding patterns identified homology of all chromosomes of subsp.villosus, but for 12 pairs only in subsp.secaliformis. Between plants, reliable identification of homology and homoeology (subsp.secaliformis) was possible only for the SAT-chromosomes and the shortest metacentrics. Chromocentres were very small and the amount of constitutive heterochromatin was low. N-banding stained chromosomes uniformly. The basic karyotypes of theP. fragilis taxa were similar to those ofP. juncea, P. lanuginosa, andP. stoloniformis supporting a close relationship and the presence of a common genome, N. NORs had different nucleolus-forming activities. Meiotic analysis demonstrated a high level of bivalent pairing in the three taxa. A chromosomal rearrangement was suggested in subsp.villosus. The low multivalent frequency in subsp.secaliformis indicates the presence of a pairing regulation mechanism. The majority of chiasmata were interstitial. Pollen grain size discriminated between diploid and tetraploid taxa. The existence of a diploid cytotype of subsp.secaliformis is supported by pollen measurements of herbarium material.

Karyological Studies in the Genus Sesbania.

Detailed somatic karyotype analysis was carried out in 6 species of Sesbania. Of these, four species namely aculeata, rostrata, aegyptica and speciosa were diploid with 2n=12 chromosomes, while the species grandiflora was a tetraploid with 2n=24 chromosomes. The other species, sesban has both diploid (2n=12) and tetraploid (2n=24) cytotypes. Considerable differences were observed among the different species in terms of total chromatin length and volume with the values ranging from as high as 47.07μm and 31.98μm3 in S. qrandiflora to as low as 18.31μm and 8.98μm3 in the species S. aegyptica. All diploid cytotypes except aculeata, exhibited one pair of SAT-chromosomes each, usually the second longest in the complement. In tetraploid forms two pairs of chromosomes (chro. 1, 2) carried secondary constriction in their long arms. The karyotypes of all species except aculeata were found to be symmetric with predominanty metacentric chromosomes. S. aculeata, however, had an asymmetric karyotype with 2 pairs of sub-metacentric and 1 pair of sub-telocentric chromosomes in addition to 3 metacentric pairs. Relative lengths, S% and TF% estimations also support the above view. The occurence of diploid and tetraploid forms in S. aculeata and S. sesban suggests the possibility of the existence of tetraploid forms in other Sesbania species also.