The effect of B-chromosomes of rye on the chromosome association in F1 hybrids Triticum aestivum x Secale cereale in the absence of chromosomes 5B or 5D

Summary T. aestivum var. Chinese Spring (monosomic 5B and 5D, respectively) was crossed with S. cereale (with and without B-chromosomes). The resulting nullisomic 5B hybrids exhibited a high degree of chromosome association both at 20°C and 10°C. The presence of B-chromosomes reduced association slightly whether 5B was present or not.In nullisomic 5D hybrids B-chromosomes of rye raise chromosome association at 20°C when compared to hybrids with 5D, with as well as without, B's. At 10°C, due to the absence of the Ltp gene on 5D, chromosome association in nullisomic 5D hybrids is low, and no effects of rye B-chromosomes is detectable.The hypothesis that B-chromosomes of rye carry (an) asynaptic gene(s) decreasing effective pairing, and (an) independent post-synaptic gene(s) increasing chiasma frequency on effective pairing sites, is presented.The work was supported by a fellowship of the Gulbenkian Foundation and partly carried out while the author was at the Department of Genetics, Agricultural University, Wageningen, the Netherlands     

Interaction between rye B-chromosomes and wheat genetic systems controlling homoeologous pairing

The interactive effect on homoeologous pairing of rye B-chromosomes with the absence of both pairing suppressor (3A, 3D, 5B) and promotor (3B, 5A, 5D) chromosomes of common wheat (Triticum aestivum L.) is analyzed by comparison of pairing at Metaphase I of 27-, 27+2B, 28- and 28+2B-chromosome plants. These plants were obtained from crosses between the respective wheat monosomics (2n=41) and rye plants (Secale cereale L.) carrying or not carrying two B-chromosomes (2n=14 or 14+2Bs). —The effect of rye B-chromosomes on pairing depends on the function of the wheat chromosome which is absent in the appropriate hybrids, i.e., rye B-chromosomes have a suppressor effect on pairing when the pairing suppressing wheat chromosomes 3A, 3D or 5B are absent, while they behave as promotors when the pairing promoting chromosomes 3B, 5A or 5D are absent.     

Molecular cytogenetic characterisation of the terminal heterochromatic segment of the B-chromosome of rye (Secale cereale)

The terminal heterochromatic segments of the long arms of 20 rye B-chromosomes were isolated by means of laser microdissection technology. Also the remaining portions of the long arms, along with the short arms of the same chromosomes were isolated. Each sample was used for degenerate oligonucleotide primer-polymerase chain reaction (DOP-PCR) amplification reactions. The resulting products were used as probes for chromosome in situ hybridisation experiments, and in Southern hybridisation to digests of 0B and +B DNA. Competition hybridisation of these probes with 0B DNA allowed the detection of B-specific sequences. The terminal heterochromatin of the rye B-chromosome contains both B-specific sequences and sequences also present on the A-chromosomes of rye. The B-specific D1100 family is the major repeat species located in the terminal heterochromatin. Primers designed to the cloned sequence (E1100) were used to search for related low copy sequences in 0B DNA. The sequences of the PCR products revealed no similarities to that of the clone E1100 except for the primer sequences. The possible origin of this sequence is discussed in the context of models for the evolution of the rye B-chromosome. EMBL and Genbank accession numbers: Z54196 (E1199): Z54278 (B1) Edited by: R. Appels     

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.     

Cloning of the Telomere Associated Sequences of Rye B-chromosomes

The short arm terminal segments of 10 rye ( Secale cereal L. ) B-chromosomes were isolated by means of needle microdissection technology. A two-step single primer PCR method was used to amplify the telomere associated sequences of rye B-chromosomes. The PCR products were located in the terminal region of the short ann of rye B-chromosomes by chromosome in situ hybridization, and most A-chromosomes also showed clear signal dots. Some PCR products were cloned in pUC19 vector and one clone pp3 was sequenced. Sequence analysis demonstrated that it has high similarity with the maize subtelomeric clone pBF266. Further utility of this mierodissection-PCR system in construction of high density RFLP map was discussed.     

THE GEOGRAPHICAL DISTRIBUTION OF B-CHROMOSOMES OF XANTHISMA TEXANUM DC. (ASTERACEAE). I. SURVEY OF THE RANGE

The distribution of B-chromosomes throughout the range of Xanthisma texanum has been determined from approximately 750 individuals from 80 wild populations in Texas, Oklahoma, and New Mexico. Counts of meiotic chromosome figures of n = 4_II + 1 B_I and n = 5_II (4_II + IB_II) are reported for the first time for subsp. texanum var. texanum and for subsp. texanum var. orientalis. The wide occurrence of B-chromosomes in natural populations of subsp. drummondii is also documented. B-chromosomes are present in 22 (27.2%) randomly distributed populations whose characteristics are in no way distinct from populations without B-chromosomes. In populations with B-chromosomes present, 19.8% of the plants contained one or two B-chromosomes, but in total only 5.8 % of all plants contained one or two B-chromosomes. All populations in one isolated population group of subsp. drummondii lack B-chromosomes.     

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.     

Production of trigeneric (barley × wheat) × rye hybrids

Summary Rye (Secale cereale cv. Prolific 2n=14 and 2n =14 + 2B was crossed onto hybrids between barley (Hordeum vulgare 2n = 14) and wheat (Triticum aestivum 2n= 42). Pollinated florets were injected with GA₃ to promote fertilization and hybrid embryo development. At 16 days after pollination the watery caryopses were removed, embryos dissected and cultured on a modified B₅ medium. Approximately 20% of the cultured embryos produced both roots and coleoptile and developed into viable seedlings. Viable seeds were also obtained at a low frequency from the same cross combinations. The hybrids were wheat-like except for the hairy neck characteristic of rye. There were 35 chromosomes in somatic tissue; 21 wheat, 7 barley and 7 rye. The rye chromosomes were distinguishable by their larger size and terminal C-bands. A lower seed set was obtained using pollen from rye plants with 2n=14 + 2B chromosomes than from plants without B chromosomes.Contribution No. 577, Ottawa Research Station     

Controlled introgression to wheat of genes from rye chromosome arm 1RS by induction of allosyndesis

Summary Chromosome pairing between rye chromosome arm 1RS, present in two wheat-rye translocation stocks, and its wheat homoeologues was induced by introducing the translocations into either a ph1bph1b or a nullisomic 5B background. This rye arm carries a gene conferring resistance to wheat stem rust, but lines carrying the translocation produce a poor quality dough unsuitable for breadmaking. Storage protein markers were utilised along with stem rust reaction to screen for allosyndetic recombinants. From a 1DL-1RS translocation, three lines involving wheat-rye recombination were recovered, along with thirteen lines derived from wheat-wheat homoeologous recombination. From a 1BL-1RS translocation, an additional three allosyndetic recombinants were recovered. Nullisomy for chromosome 5B was as efficacious as the ph1b mutant for induction of allosyndesis, and the former stock is easier to manipulate due to the presence of a 5BL-encoded endosperm protein. The novel wheat-rye chromosomes present in the recombinant lines may enable the rye disease resistance to be exploited without the associated dough quality defect.     

B-chromosomes in some Himalayan hardwoods

B-chromosomes are reported for the first time for woody angiosperms. Out of six species from the eastern Himalayas in which B-chromosomes were observed, two are polyploid. The number of B-chromosomes varied from 0–5 in the different species. In Sambucus canadensis, Glerodendrum colebrookianum and Neolitsea zeylanica B's were found to pair with each other at Metaphase-I.The financial support for this work was provided by the U. S. Government from PL 480 funds in India (Grant: A7-FS-12).     

Genotype-dependent effect of B-chromosomes on chiasma frequency in Eyprepocnemis plorans (Acrididae: Orthoptera)

In order to analyze the effect of B-chromosomes on chiasma frequency, the offspring of different females of the grasshopper Eyprepocnemis plorans have been studied. From the comparison between individuals of the different families having a given number of B's and between individuals with different numbers of B-chromosomes within the same family, it can be concluded that the effect of the genetic background on chiasma frequency is greater than that produced by the presence of B's, and that there is a between-families variation in the effect of B-chromosomes which, in addition, is negatively correlated with the chiasma frequency of related individuals without B's. This genotype-dependent effect of B-chromosomes is discussed.     

A Preliminary Observation on B-Chromosomes of Regal lily

The authors have observed t he karyotypes of the Regal Lily with B-chromosome and without B-chromosomes as well as their Giemsa C-bands. The results show that the karyotypes with B-chromosomes are not obviously different from those without B- chromosomes. B-chromosome is additional and all of them are heterochromatization. But segregation of B-chromosome at anaphase Ⅰ and Ⅱ in meiosis is irregular, and about half of the pollen grains contain B-chromosomes. In the progenies by open pollination the segre, gation of 0B and lB appear in the ratio near 1:1 and the offsprings with 2B-chromosomes only average 2.6 percent.     

Isolation of a sequence common to A- and B-chromosomes of rye (Secale cereale) by microcloning

The techniques of microdissection and microcloning have been applied to the isolation of B-chromosome DNA from rye. We have identified a DNA sequence on the rye B-chromosome which is homologous to an A-chromosome sequence, and which is dispersed and moderately repeated on the A- and B-chromosomes. This demonstrates that the rye B-chromosome is heterogeneous in the nature of its DNA sequence composition, containing sequences which are present on the A-chromosomes in addition to those not present on the A-chromosomes.     

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.     

B-chromosomes in inbred lines of rye (Secale cereale L.)

B-chromosomes from an experimental population of the Japanese JNK strain of rye, isogenic for its Bs, have been backcrossed into twelve different inbred lines. The experiment provides a way to study the effects of the Bs against a range of homozygous A-chromosome backgrounds. This publication deals with vigour and fertility: it shows that the rye Bs fit a parasitic model, and that they interact in their effects with the A-chromosome background genotype.     

Cytogenetic Analysis of A- and B-Chromosomes of Prochilodus Lineatus (Teleostei, Prochilodontidae) Using Different Restriction Enzyme Banding and Staining Methods

Different cytogenetic techniques were used to analyse the chromosomes of Prochilodus lineatus with the main objective of comparing the base composition of A- and B-chromosomes. The results of digestion of chromosomes with 10 different restriction endonucleases (REs), silver staining, CMA₃ staining and C-banding indicated the existence of different classes of highly repetitive DNA in the A-set and also suggested the existence of compositional differences between the chromatin of A- and B-chromosomes. The 5-BrdU incorporation technique showed a late replicating pattern in all B-chromosomes and in some heterochromatic pericentromeric regions of A-chromosomes. The cleavage with RE BamHI produced a band pattern in all chromosomes of P. lineatus which permitted the tentative pairing of homologues in the karyotype of this species. We concluded that the combined use of the above techniques can contribute to the correct identification of chromosomes and the karyotypic analysis in fishes. On the basis of the results, some aspects of chromosome structure and the origin of the B-chromosomes in P. lineatus are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Variable transmission rates of a B-chromosome in Myrmeleotettix maculatus (Thunb.) (Acrididae: Orthoptera)

Karyotype comparisons of both parents and progeny from single pair matings in the grasshopper Myrmeleotettix maculatus have shown that there is an accumulation of the large mitotically stable B-chromosome when transmitted through the female. This is presumed to result from a preferential segregation of univalent B-chromosomes at the first division of female meiosis and occurs irrespective of whether the B's are odd or even in number. In the male there is a loss of B-chromosomes. This loss does not appear to be due simply to the lagging and elimination of B-chromosomes in meiosis but probably involves sperm formation or function. When the balance of the gain and loss after one generation is calculated, it shows large overall accumulation in crosses involving individuals from a population in Wales, and a slight loss in individuals from a population in East Anglia. Such differences in transmission rates may be responsible for differences in B-frequency between populations. Since the B-chromosome frequency of these two populations has remained stable over five years, possible forces in the maintenance of the equilibria are examined. Females with B-chromosomes produce more aneuploid embryos than 0B females, but neither this cause of inviability nor general embryo mortality seem sufficient to produce an equilibrium situation. It is necessary to postulate that progeny with more than 2B chromosomes are inviable in order to approach equilibria. The presence of B-chromosomes in females has also led to the formation of polyploid embryos. The possible involvement of repetitive DNA in the formation of unreduced egg nuclei and preferential segregation is discussed.     

The B-chromosome system of Hypochoeris maculata

The stable telocentric B-chromosomes of Hypochoeris maculata show an overall accumulation through the egg but a loss through the pollen. When crosses involve a single B^t the joint transmission gives an accumulation of 8%. The individual crosses, however, show great heterogeneity. Transmission through the megaspore ranged from 0.287 to 1.037 per B while pollen transmission was much less variable (0.360 to 0.560 per B) and close to the expected value. There is no intraplant correlation between pollen and egg transmission. Crosses repeated in different years show a clear positive correlation through the egg but no correlation through the pollen indicating that some B-transmission variation is of environmental origin. Despite this discrepancy, the outcome of crosses between plants of known transmission rate can be predicted. Stability of the A-chromosome complement is clearly reduced by the presence of B-chromosomes.     

The B-chromosome system of myrmeleotettix maculatus (thunb.)

It is established that in populations of Myrmeleotettix maculatus with B-chromosomes these chromosomes occur at stable frequencies and are present to the same extent in both the males and the females of the same population. It is also established that the B-chromosome content of a population is positively correlated with its chiasma frequency and that, within a population, individuals with single B-chromosomes tend to have higher chiasma frequencies than individuals lacking B-chromosomes. Since this effect is not increased by the addition of further supernumeraries it is argued that selection operates in favour of individuals with single B-chromosomes. Finally it is shown that the level of B-chromosomes in a population is related to temperature and especially to rainfall so that B-chromosomes are absent from populations in climatically stringent environments.     

Differential staining of plant chromosomes with Giemsa

Simple Giemsa staining techniques for revealing banding patterns in somatic chromosomes of plants are described. The value of the methods in the recognition of heterochromatin was demonstrated using five monocotyledonous and two dicotyledonous species. In Trillium grandiflorum the stronger Giemsa stained chromosome segments were shown to be identical with the heterochromatic regions (H-segments) revealed by cold treatment. Preferential staining of H-segments was also observed in chromosomes from three species of Fritillaria and in Scilla sibirica. Under suitable conditions the chromosomes of Vicia faba displayed a characteristic banding pattern and the bands were identified as heterochromatin. The Giemsa techniques proved to be more sensitive than Quinacrine fluorescence in revealing a longitudinal differentiation of the chromosomes of Crepis capillaris, where plants with and without B-chromosomes were examined. Again all chromosome types had their characteristic bands but there was no difference in Giemsa staining properties between the B-chromosomes and those of the standard complement.