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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and applied genetics 55 (1979), S. 205-208 
    ISSN: 1432-2242
    Keywords: Triticinae ; Low temperature ; Variation ; Chromosome pairing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Hybrids of Triticum aestivum (monosomic 5D or ditelosomic 5DL) x T. speltoides (= Ae. speltoides) showed that the genotype of T. speltoides carries gene(s) which can partially compensate for the expected decrease in chromosome association at low temperatures (10°C) in the absence of chromosome 5D. In hybrids of T. aestivum (normal, ditelosomic 3DL or ditelosomic 3DL-monosomic 5D) x T. longissimum (= Ae. sharonensis), this compensation was not observed. In normal F1 hybrids of T. durum x T. longissimum partial chromosome association occurred at 10°C and this stabilizer effect may be explained by the presence of a Ltp-like gene on chromosome 5A. When a line of T. durum carrying a homozygous translocated 5B-5D chromosome was used in the crosses an even higher chromosome association was observed. These results suggest either the existence of a promoter gene for chromosome association in the 5D translocated segment or the loss of a weak suppressor gene in the removed segment of 5B. It was concluded that the translocated 5D segment did not carry the Ltp stabilizer gene.
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  • 2
    ISSN: 1432-2242
    Keywords: B-Chromosomes ; Chromosome associations ; Triticum aestivum ; Secale cereale hybrids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: 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.
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  • 3
    ISSN: 1432-2242
    Keywords: Nucleolar dominance ; Genomic imprinting ; NOR expression ; Silver staining
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Ribosomal RNA genes originating from one parent are often suppressed in interspecific hybrids. We show that treatments during germination with the cytosine analogue 5-azacytidine stably reactivate the expression of the suppressed rRNA genes of rye origin in the wheat x rye amphiploid, triticale, by preventing methylation of sites in the rye rDNA. When 5-azacytidine is applied to embryos of triticale and wheat x rye F1 hybrids nine, or more, days after fertilization, rye rRNA gene expression is stably reactivated in the resulting seedling. Earlier treatments have no effect on rye rRNA gene expression, indicating that undermethylation of DNA early in embryo development is reversible. After 9 days, the methylation status of rRNA genes in maintained throughout development. Since the change in expression follows a methylation change at particular restriction-enzyme sites, the data establish a clear correlation between gene activity and methylation in plants.
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  • 4
    ISSN: 1573-6849
    Keywords: B chromosomes ; interphase chromatin ; rDNA organization ; rye
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Patterns of rye rDNA organization in interphase nuclei were studied through the use ofin situ hybridization in spreads of root meristem cells from plants with and without B chromosomes (Bs). In cells from plants without Bs each rDNA locus is organized as a single perinucleolar knob of condensed chromatin with decondensed chromatin inside the nucleolus. In plants with Bs there is a marked modification of the pattern, found in more than 23% of nuclei, which involves several regions of condensed chromatin interspersed with decondensed chromatin inside the nucleolus. This B-induced alteration in rDNA interphase organization suggests a change in expression of the rRNA genes located on the A chromosomes probably related to the reduction in nuclear RNA observed previously in plants with Bs. The influence of the Bs on the expression of A chromosome genes, through rearrangement of interphase chromatin, could provide the basis of an explanation for some of the known phenotypic effects of B chromosomes in rye.
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  • 5
    ISSN: 1573-6849
    Keywords: B chromosomes ; genomicin situ hybridization ; nuclear architecture ; Secale cereale ; Triticum aestivum cv ; Lindström
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The B chromosomes (Bs) of rye (Secale cereale) have been studied at interphase in terms of their chromatin organization, patterns of nuclear disposition and physical association in plants with two, three, and four Bs. The study was made in the Lindström strain of hexaploid wheat, which carries the rye Bs as an addition line, byin situ hybridization with a B-specific probe and by genomicin situ hybridization (GISH) with rye genomic DNA, enabling whole chromosome painting. Repetive sequences common to the As and Bs of rye allow for visualization of the rye B at interphase in the wheat background. A B-specific probe enables the orientation of two or more Bs to be determined, and the combination of both probes used together gives information on the disposition of the Bs and on their patterns of physical association within the nucleus. The Bs form linear ‘strings’, and the ends of their long arms, which can be detected by the B-specific probe, are usually located within the hemisphere of the nucleus that has the least condensed chromatin. There is dose-dependent association, and even numbers (2B, 4B) have a greater preference for association than odd ones (3B).
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  • 6
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Genetica 51 (1979), S. 69-75 
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Genetica 51 (1980), S. 233-239 
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Chromosome research 5 (1997), S. 125-131 
    ISSN: 1573-6849
    Keywords: gene expression ; nucleolar dominance ; rDNA ; substitution lines ; triticale
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Hybrid plants and animals often show suppression of activity of ribosomal genes (rDNA) originating from one of the parental or ancestral species. In the wheat × rye amphiploid triticale, containing 28 chromosomes of wheat origin and 14 from rye, rDNA of rye origin (on chromosome 1R) is not normally expressed, while the 1B- and 6B-origin rDNA from wheat shows strong expression. Expression of rDNA can be accurately assessed by the silver staining method, which stains both interphase nucleoli and metaphase rDNA sites that were actively expressed at the previous interphase. We show here that substitution of another rye chromosome, 2R, by a chromosome from hexaploid wheat, 2D(triticale-2D(2R)), prevents suppression of the rye-origin rDNA, and leads to activity of all six major rDNA loci. These results were found in two different triticales and supported by rDNA behaviour in wheat—rye chromosomal addition lines. Models for chromosomal interactions leading to control of rDNA expression are presented.
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  • 10
    ISSN: 1573-6849
    Keywords: genomic imprinting ; intergenomic interactions ; 1R nucleolar organizer region ; seed development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To identify the developmental stage during which the preferential inactivation of rRNA genes from the rye parent occurs in wheat × rye hybrids, nucleolar activity was evaluated in the embryo and endosperm of developing seeds of the hybrids. The hybrids were obtained from crosses of euploid and aneuploid lines of hexaploid wheat,Triticum aestivum cv. Chinese Spring, with rye,Secale cereale cv. Centeio do Alto. The number of nucleolar organizing regions (NORs) and nucleoli present in the embryo and endosperm cells of wheat, and wheat × rye F1 hybrids, at different times after fertilization was scored by silver staining. The inactivation of rDNA of rye origin in F1 hybrids occurs simultaneously in the embryo and in the endosperm between 4 and 5 days after fertilization, when these have been through six and 10 cell cycles respectively. We conclude that the genomic interactions leading to the inactivation of the rye origin rDNA is a time-dependent process, related to the developmental stage and independent of the number of cell cycles (DNA replication rounds) they have been through.
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