Structure,behaviour and repetitive DNA of B-chromosomes in Cestrum nocturnum (Solanaceae)

Abstract

The Cestrum genus is karyotypically exceptional in Solanaceae. It is characterised by a basic number x?=?8, a large chromosomal and genomic size, complex heterochromatin patterns, B-chromosomes (Bs) with particular heterochromatin and distribution of 18–5.8–26S and 5S rDNA. Cestrum nocturnum L. has a diploid number of 2n?=?16 plus a variable number of B-chromosomes. The aims of work was to analyse their numerical variation, structure and behaviour of C. nocturnum B-chromosomes by classical and molecular cytogenetics. The individuals analysed had 2n?=?16?+?0?13 B-chromosomes. All B-chromosomes were metacentric and smaller than A-chromosomes. The number of B-chromosomes showed a great variability between and within individuals, thereby denoting the occurrence of events that promote mitotic and meiotic instability. Cytogenetic techniques made it possible to observe that B-chromosomes are rich in heterochromatin, probably with AT- and GC-rich regions. In addition, molecular techniques allowed to detect homologous sequences of transposable element conserved domains of Ty1-Copia and Ty3-Gypsy superfamilies. These sequences were located by FISH in all B-chromosomes and some A-chromosomes. Our results showed that repetitive DNA could play an important role in chromosomal evolution as well as in the stability of B-chromosomes in C. nocturnum.     

Evidence of B-chromosomes in the karyotype of Barypeithes pellucidus Boheman 1834 (Coleoptera, Curculionidae, Entiminae) from Central Europe

B-chromosomes were observed in spermatogonial mitotic metaphases, meiotic metaphases I and II of Barpeithes pellucidus from one population in Slovakia. The number of B-chromosomes ranged from one to six per cell and they paired with the sex heterochromosomes in the first meiotic metaphase and rarely with the autosomes. In metaphase I one B-chromosome was always associated with X chromosome forming a tripartite complex. The XyBp was easily recognizable as a complex of three chromosomes in a parachute association The size of the B-chromosomes was approximately the same or a little smaller than that of the y heterochromosome which was the smallest element of the regular chromosome set. Their staining intensity seems to be similar to that of the autosomes and sex chromosomes, respectively. The behaviour of B-chromosomes during mitosis and meiosis in weevils is briefly discussed.     

Occurrence and behaviour of B chromosomes in Artemisia frigida Willd.

In A. frigida Willd., B-chromosomes are reported for the first time. Their number was limited to 2 in all the cells studied. Analysis of chromosome behaviour at meiosis showed that B-chromosomes reduced the mean chiasma frequency and modified the phenotypic and biochemical characteristics of the plants.     

Karyological features of the Siberan spruce Obovata ledeb. from various locations

Results of karyological study of the Siberian spruce from different provenances are presented. A comparative idiogramm for the Siberian spruce from Krasnoyarsk Territory and the Khakass Autonomous Region was constructed. In addition to the typical chromosome number (2n = 24), the Siberian spruce has one or two B-chromosomes (2n = 24 + 1B; 2n = 24 + 2B). Hereditary transmission of B-chromosomes and their behaviour in mitosis have been studied. It is supposed that B-chromosomes of the Siberian spruce have a nucleolar-organizing ability.     

Instability of B-chromosomes in somatic and germline cells of Apodemus peninsulae

Instability of B-chromosomes was estimated in somatic and germline cells of samples Apodemus peninsulae from different localities of the species range. In 84 out of 188 animals (45%), in cells assessed for B-chromosome mosaicism, bone marrow cells with different B-chromosome number were observed. The numbers of B-chromosomes in spermatocytes at the pachytene stage were estimated in ten males. It was shown that the average number of B-chromosomes and the number of cell clones in germline cells was higher than the corresponding numbers in bone marrow cells. The higher number of B-chromosomes and their higher variability in germline cells than in somatic cells suggest the existence of a mechanism of premeiotic accumulation of B-chromosomes in spermatogenesis of A. peninsulae.     

Chromosomes in a hybrid zone of Israeli mole rars (Spalax, Rodentia)

Chromosomal novelties and the level of meiotic and mitotic abnormalities were studied in a hybrid zone between two chromosomally differentiated Spalax cytotypes of 2n = 58 and 2n = 52. These cytotypes differ by five Rb fusions, four centromeric shifts accompanied by heterochromatin deletion, one paracentric inversion, and the Y-chromosome reorganization. Among 149 specimens studied, 82 were hybrids with 64 different karyotypes ranging in diploid numbers from 2n = 50 to 2n = 60. Nine hybrid specimens were mosaics for the chromosome numbers due to occurrence of cell lines with different Robertsonian chromosome arrangements, and six specimens possessed variable number of B-chromosomes. Mosaicism of B-chromosomes was found also in meiotic cells however chromatid breaks and abnormal chromosome pairing during meiosis occurred very rarely. All these results imply some local genomic instability resulting in the spontaneous process of reversible Rb fusions.     

Presence and behaviour of B-chromosomes in Acanthophyllum laxiusculum (Caryophyllaceae)

Two karyotypic variants were recognized in populations of Acanthophyllum laxiusculum Schiman-Czeika. Variant A had 2N = 30 and variant B showed the presence of 0 to 3 B-chromosomes in addition to 2N = 30 chromosomes. Analysis of chromosome behaviour at meiosis showed that the presence of B-chromosomes increases chiasma frequency in A-chromosomes; this effect was higher for plants with odd numbers of B-chromosomes compared with plants with even numbers of B-chromosomes. Comparisons of variants A and B, suggests that B-chromosomes have an effect pollen stainability and seed production. It seems that the presence of B-chromosomes may increase pollen stainability and seed production in variant B.     

Instability of B-chromosomes in somatic and germline cells of Apodemus peninsulae

Instability of B-chromosomes was estimated in somatic and germline cells of samples Apodemus peninsulae from different localities of the species range. In 84 out of 188 animals (45%), in cells assessed for B-chromosome mosaicism, bone marrow cells with different B-chromosome number were observed. The numbers of B-chromosomes in spermatocytes at the pachytene stage were estimated in ten males. It was shown that the average number of B-chromosomes and the number of cell clones in germline cells was higher than the corresponding numbers in bone marrow cells. The higher number of B-chromosomes and their higher variability in germline cells than in somatic cells suggest the existence of a mechanism of premeiotic accumulation of B-chromosomes in spermatogenesis of A. peninsulae     

Synaptonemal complexes of the A- and B-chromosomes of the spermatocytes from the East Asian mouse Apodemus peninsulae

The analysis of whole-mount preparations of synaptonemal complexes (SCs) from surface-spread spermatocytes of A. peninsulae (2n = 48A + 1, 2, ... 12 B) had revealed SCs of 23 autosomal bivalents, sex bivalent XY, axial cores and SCs of the B-chromosomes. The intercellular and interindividual variability of the number of B-chromosomes varied from 1 to 12 per cell. The SCs of autosomal bivalents were shown to have a typical structure. The structure and behaviour of SCs of sex bivalent throughout meiotic prophase I appeared to be similar to those observed in other species of this order. Mainly B-univalents and less frequently B-bivalents containing SCs were found to be formed in meiotic prophase I. The full homologues appear to be rarely seen among B-chromosomes of the East-Asiatic mouse. A tendency of forming clusters of B-univalents near the sex bivalent was found, in addition to B-bivalents with lateral elements, having the form of bi- and tri-stranded elements with rare synaptic fragments. Besides this, the SCs of the autosomes of pachytene cells were found to contain structures resembling the recombination nodules.     

兰州百合B染色体的初步研究

对兰州百合具B染色体的细胞在有丝分裂和减数分裂过程中的行为进行了观察。结果表明,B染色体数在0～3之间变化,在有丝分裂和减数分裂中均高度异染色质化,分离具有不定向性,出现少量累积。通过比较两种生境中B染色体出现的频率,认为B染色体的有或无可能与兰州百合的适应性有关。     

Chromosomes in a hybrid zone of Israeli mole rars (Spalax, Radentia)

Chromosomal novelties and the level of meiotic and mitotic abnormalities were studied in a hybrid zone between two chromosomally differentiated Spalax cytotypes of 2n = 58 and 2n = 52. These cytotypes differ by five Rb fusions, four centromeric shifts accompanied by heterochromatin deletion, one paracentric inversion, and the Y-chromosome reorganization. Among 149 specimens studied, 82 were hybrids with 64 different karyotypes ranging in diploid numbers from 2n = 50 to 2n = 60. Nine hybrid specimens were mosaics for the chromosome numbers due to occurrence of cell lines with different Robertsonian chromosome arrangements, and six specimens possessed variable number of B-chromosomes. Mosaicism of B-chromosomes was found also in meiotic cells however chromatid breaks and abnormal chromosome pairing during meiosis occurred very rarely. All these results imply some local genomic instability resulting in the spontaneous process of reversible Rb fusions.     

B chromosome polymorphism of blackflies (Diptera, Simuliidae) from the north-western region of Russia

We have studied karyofonds of natural populations and B-chromosome morphology of 8 species of blackflies from the North-Western region of Russia: Odagmia ornata Mg., Hellichiella crassa Rubz., Simulium morsitans Edw., Simulium argyreatum Mg., Shoenbaueria pusilla Fries., Cnetha fontinalis Radzv., Stegopterna duo-decimata Rubz., and Archesimulium tuberosum Lundstr. For this purpose we made slides of squashed blackflies larvae with salivary gland polytene chromosomes stained by aceto-orcein, in addition to similarly stained slides with mitotic chromosomes from gonads and ganglia. Morphology of polytene B-chromosomes of Shoenbaueria pusilla Fries., Cnetha fontinalis Radzv., Stegopterna duodecimata Rubz., and Archesimulium tuberosum Lundstr. has been first described. B-chromosome polymorphism was found in all species, but the number of B chromosomes was conserved within each differences in polytene individual. Stable and distinct interspecific differences in the morphology of polytene B-chromosomes were demonstrated, and these characters are advisable to use to distinguish the species. We have investigated for the first time karyofonds of Od. ornata populations from Arkhangelsk Region (Solovetskie Islands) and Leningrad Region (railway station Sablino), and those of S. argyreatum populations from Murmansk Region (Kandalaksha environs) and Karelia (railway station Chupa). A long term study of Od. ornata and S. argyrestum population from North-Western Russia revealed interspecific and interpopulation dynamics of the occurrence of specimens with B-chromosomes. Some populations showed an increased percentage of individuals with B-chromosomes. It is suggested that B-chromosomes may play a role in adaptation of polulations to severe environmental conditions.     

Influence of B-chromosomes on meiosis in pearl millet

B-chromosome behaviour and the effects of B's on the endophenotype were studied in the third back-cross progeny of a cross between non-B and B-carrying parents ofPennisetum typhoides Stapf et Hubb. In the experimental material a regular increase in B-chromosome chiasma frequency and an increase in the variation of mean chiasma frequency with increased number of B's was observed. When four or more B-chromosomes were present quadrivalents occurred more frequently. In these respects the experimental material differed from the B-carrying parent. B's had no effect on the mean chiasma frequency of A-chromosomes when present in numbers of up to and including four but when present in numbers of more than four had a depressing effect. The variation of the mean chiasma frequency of the A-chromosomes increased with increasing number of B's. No correlation was observed between A-chromosome chiasma frequencies and B-chromosome chiasma frequencies. In the experimental material B's when present in larger numbers i.e. more than four had deleterious effects on A-chromosome behaviour and on fertility. In the effects of B's on the endophenotypic characters the experimental material differed from the B-carrying parent. It is suggested that the behaviour and effects of B's on the endophenotypic characters are the result of interaction between the A-chromosome genotype and the B-chromosomes.     

B-Chromosomen beiChironomus

In the population “Herrenmühle” ofChironomus plumosus 11% of the individuals contain one supernumerary chromosome. This B-chromosome is present both in germ-line and somatic cells. — InChironomus melanotus 6% of the larvae of the population “Falkau” carry supernumerary chromosomes. These B-chromosomes cannot be found in all nuclei of testis and soma, their number varies between cells within the individual. In both species the B-chromosomes represent centromeric fragments of chromosome IV as can be shown by their structure and pairing behaviour. — The polytene B-chromosome ofCh. plumosus exhibits a banding pattern in the salivary gland nuclei. Furthermore it is able to form an additional nucleolus in the nuclei of the malpighian tubules. InCh. melanotus band structures can be seen only in the B-chromosome of malpighian tubules. The larvae ofCh. melanotus, carrying B-chromosomes, show heterochromatic bodies in the salivary gland nuclei, varying in number and size in the nuclei of the same gland. These bodies are interpreted to be polytenic B-chromosomes divided into subunits.

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Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

THE CYTOGENETICS OF XANTHISMA TEXANUM DC. (ASTERACEAE) AND ITS B-CHROMOSOMES

The karyotype of A-set and B-chromosomes of Xanthisma texanum DC. are described in detail and measurements are given. The distribution of B-chromosomes in stem tissue is described and the loss of B-chromosomes from primary roots confirmed. The number of B-chromosomes in pollen mother cells was constant within single inflorescence buds and in all buds throughout the flowering period. The behavior of one and two B-chromosomes during meiosis is described in detail. During meiosis, B₁'s divided in 71% of the cases during anaphase II and in 29% of the cases during anaphase I. First anaphase division resulted in some lagging and elimination of B-chromatids during second division. During anaphase I, B₁₁'s divided into chromosomes and in anaphase II these divided into chromatids in 95% of the cases. In the other 5 % non-disjunction of the B-chromosomes or chromatids and A-set chromosome abnormalities occurred. Post meiotic preferential distribution during pollen mitosis resulting in a doubling of the number of B-chromosomes passed to progeny via pollen occurred, but no doubling occurred in the female line. Crosses involving plants with two B-chromosomes each yielded fewer plants with three B-chromosomes than expected. Polyploidy is extremely rare in the species. The evolutionary significance of B-chromosome behavior is discussed in relation to its origin and survival.     

Nature and role of accessory chromosomes in silver-gray foxes. IV. The behavior of accessory chromosomes in meiosis

Comparison of chromosome number at somatic and spermatogonial mitoses has demonstrated the increase in the number of additional chromosomes in cells of germinal tissue. This may evidence a mechanism of B-chromosomes accumulation in foxes. B-chromosomes may lag as univalents, may form bivalent associations, or occasionally form trivalents at the stage of diakinesis-metaphase I, and they may associate with macrobivalents (A-chromosome bivalents). The analysis of metaphase II has shown that the distribution of B-chromosomes in the second metaphase is random resulting in gametes with various numbers of B-chromosomes.     

Synaptonemal complex analysis of B-chromosome behavior in meiotic prophase I in the East-Asiatic mouse Apodemus peninsulae (Muridae, Rodentia)

The mitotic and meiotic chromosomes of four male East-Asiatic mice, Apodemus peninsulae, having three to seven chromosomes in addition to the standard karyotype (2n = 48), were investigated. B-chromosomes were represented by medium-sized metacentric and dotlike chromosomes. Mosaicism of bone marrow cells due to a numerical variation of accessory chromosomes was established for the males examined. Capacity of B-chromosomes to form axial elements and synaptonemal complexes in meiotic prophase I was revealed by electron microscopy. The occurrence of univalents of different morphology, bivalents, and multivalents, corresponding to B-chromosomes, was demonstrated. An increase in the number of B-chromosomes was found in spermatocytes at zygotene-pachytene relative to the number in bone marrow cells, which may be evidence of B-chromosome accumulation in the germ cell line of the East-Asiatic mouse.     

银额果蝇的B染色体研究:1.昆明群体的Bs数目和频率

本研究发现银额果蝇昆明群体有丝分裂中期核型中存在B染色体,出现频率为69.1%。目前,在已研究过的来自各个地区的银额果蝇中,昆明群体的B染色体频率最高。B染色体数目为1-6条。该群体内单雌系间的B染色体数目不同,个体间和细胞间的B染色体数目也不同。在核型中,B染色体最小,形态稳定,点状,C-带和G-带呈阳性。     

Cytogenetic differentiation of Apodemus peninsulae populations (Rodentia, Muridae) in eastern Siberia

Population and cytogenetics studies of geographical karyotype changes in East Asiatic mice in East Siberia showed that each population has unique cytogenetic structure, owing to different variants of B-chromosomes system, including 1 to 18 B-chromosomes differing in morphology and size. For each population, we observed the prevalence of mice with a definite number and morphology of B-chromosomes, which is probably the result of homeostatic processes in the population. Local changes were revealed, due to increase in the number of dot-like B-chromosomes in the direction from the West to the East.     

B-chromosome polymorphism and interchromosomal chiasma interference in Eyprepocnemis plorans (Acrididae; Orthoptera)

Using the C-banding technique, the morphology and meiotic behaviour of four different types of B-chromosomes present in several populations of Eyprepocnemis plorans have been studied. The possible relationship between these four types is discussed. The analysis of chiasma frequency in A and B-chromosomes suggests the existence of interchromosomal interference and demonstrates that the chiasma frequency of B-s depends on the genetic background of the individual carrying them.