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  • 1
    Electronic Resource
    Electronic Resource
    Nuclear DNA changes within Helianthus annuus L.: variations in the amount and methylation of repetitive DNA within homozygous progenies (1996)
    Springer
    Theoretical and applied genetics 92 (1996), S. 285-291 
    Details
    ISSN: 1432-2242
    Keywords: Helianthus annuus ; Intraspecific DNA changes ; Repetitive DNA ; DNA methylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Complex alterations in the redundancy and methylation of repeated DNA sequences were shown to differentiate the nuclear genome of individuals belonging to single progenies of homozygous plants of the sunflower. DNA was extracted from seedlings obtained from seeds collected at the periphery of flowering heads (P DNA) or from seedlings obtained from seeds collected in their middle (M DNA). Three fractions of repeated sequences were isolated from genomic DNA: a highly repetitive fraction (HR), which reassociates within an equivalent Cot of about 2 × 10-1, and two medium repetitive fractions (MR1 and MR2) having Cot ranges of about 2 × 10-1-2 and 2-102, respectively. Denaturation kinetics allowed different sequence families to be recognized within each fraction of repetitive DNA, and showed significant differences in sequence redundancy to occur between P and M DNA, particularly as far as the MR2 fraction is concerned. Most DNA sequence families are more represented in P DNA than in M DNA. However, the redundancy of certain sequences is greater in the latter than in the former. Each repetitive DNA fraction was hybridized to Southern blots of genomic P or M DNA which was digested to completion by three pairs of isoschizomeric restriction endonucleases which are either insensitive or sensitive to the methylation of a cytosine in the recognition site. The results obtained showed that the repetitive DNA of H. annuus is highly methylated. Clear-cut differences in the degree of methylation of P and M DNA were found, and these differences were particularly apparent in the MR2 fraction. It is suggested that alterations in the redundancy of given DNA sequences and changes in their methylation patterns are complementary ways to produce continuous genotypic variability within the species which can be exploited in environmental adaptation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00223670
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  • 2
    Electronic Resource
    Electronic Resource
    Nuclear DNA changes within Helianthus annuus L.: cytophotometric, karyological and biochemical analyses (1986)
    Springer
    Theoretical and applied genetics 73 (1986), S. 20-26 
    Details
    ISSN: 1432-2242
    Keywords: Helianthus annuus ; Intraspecific DNA changes ; Cytophotometry ; Karyology ; Chemicophysical DNA characterization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cytophotometric measurement of the root meristems of seedlings after Feulgen-staining reveals that large differences (up to 58.16%) in nuclear DNA content may occur in the thirty-one cultivated varieties or lines of Helianthus annuus tested. Significant variations (not exceeding 25%) in the amount of DNA, which does not differ between the root and the shoot meristems of a single seedling, are also found to exist within cultivars or lines; even seedlings obtained from seeds collected from different portions of single heads of plants belonging to a selfed line may vary one from the other in this respect. Variations in the number of chromosomes or alterations in the chromosome structure do not account for the differences observed in nuclear DNA content. Karyometric analyses demonstrate that the surface area of squashed interphase nuclei and metaphase chromosomes and the total length of the latter increase with the increase in Feulgen/DNA absorption. DNA thermal denaturation and reassociation kinetics indicate that a frequency variation in repeated DNA sequences goes hand in hand with changes in the size of the genome. These results, supporting the concept that a plant genome is highly flexible, are discussed in relation to other data to be found in the literature on the intraspecific variation in the nuclear DNA content and in relation to the way in which it is produced in H. annuus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00273713
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  • 3
    Electronic Resource
    Electronic Resource
    Nuclear DNA changes within Helianthus annuus L.: origin and control mechanism (1989)
    Springer
    Theoretical and applied genetics 77 (1989), S. 12-16 
    Details
    ISSN: 1432-2242
    Keywords: Helianthus annuus ; DNA cytophotometry ; Intraspecific DNA changes ; Plant embryo development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Previous results suggested that the amount of nuclear DNA varies in one and the same progeny of Helianthus annuus, depending on the head portion in which seeds have developed. Accordingly, cytophotometric determinations were carried out in a selfed line, after Feulgen-staining, to obtain information on the developmental stages at which DNA changes are produced and on the mechanism controlling the variation. It was found that the Feulgen absorption values of mitotic prophases in immature anthers and pistils and of meiotic prophases I are the same in any flower of the head. In contrast, the Feulgen/DNA contents of early prophases in heart-shaped embryos differ significantly, increasing from those developing at the centre of the head to those developing at its periphery, and remaining unchanged in each embryo during further development and seed germination. Variations in the number of chromosomes do not account for the differences observed in nuclear DNA contents in which sequences comprised in heterochromatic nuclear regions are involved. The Feulgen absorption values of seedlings obtained from seeds developed in different portions of single heads increase or diminish starting from those found in the mother plant. This depends on whether these latter are relatively low or high and on the gradient of seed location in the head. The variation occurring within each single progeny covers the whole range existing within the line.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00292309
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  • 4
    Electronic Resource
    Electronic Resource
    Nuclear DNA changes within Helianthus annum L.: changes within single progenies and their relationships with plant development (1993)
    Springer
    Theoretical and applied genetics 85 (1993), S. 506-512 
    Details
    ISSN: 1432-2242
    Keywords: Helianthus annuus ; Intraspecific DNA changes ; Cell proliferation ; Cell phenotype ; Plant development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The variations in the basic nuclear DNA content, which previous results indicated to occur within one and the same progeny of Helianthus annuus, were studied in detail and correlated with certain developmental features of the plants. The size and organization of the genome of seedlings obtained from seeds (achenes) collected at the periphery (P-seedlings) or in the middle (M-seedlings) of the flowering heads of plants belonging to a line selfed for 10 years were compared. Cytophotometric determinations indicated that the nuclear DNA content of P-seedlings is 14.7% higher than that of M-seedlings. Thermal denaturation and reassociation kinetics of extracted DNAs showed that variations in the redundancy of repetitive DNA, in particular of a family of medium repeated sequences with a Cot range of 2–100, account for the differences in genome size. These findings were confirmed by the results of molecular hybridizations (slot blots), which also indicated a higher amount of ribosomal DNA in the P-seedlings than in the M-seedlings. Cell proliferation is affected by DNA content, and mitotic cycle time is 1h30′ longer in the P-seedlings. By studying mature plants, positive correlations were also found between genome size and both the surface area of leaf epidermal cells (P≤0.01) and flowering time (P≤0.001). It is suggested that the variations of nuclear DNA content and organization observed play a role in determining developmental variability in plant populations, which may be of importance in buffering the effects of changing environmental conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00220906
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