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  • 1
    ISSN: 1432-2145
    Keywords: Key words Apomixis ; Apospory ; Hieracium ; Seed ; Modifiers ; Adventitious embryony
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Apomixis is facultative in characterized members of the genus Hieracium. The three components that comprise the apomictic mechanism include apospory followed by autonomous embryo and endosperm formation. The time of aposporous embryo sac initiation and mode of embryo sac formation are different in Hieracium piloselloides (D3) and Hieracium aurantiacum (A3.4). Genetic studies have shown that a single dominant locus encodes all three components of apomixis in both species (Bicknell et al. 2000). We histologically examined a range of related, genetically characterized apomictic Hieracium plants derived from D3 and A3.4 to assess conservation of the apomictic mechanism in different genetic backgrounds. The plants varied in ploidy, and also in the amount of DNA introduced from sexual Hieracium pilosella (P4). An apomictic hybrid from a cross between the two apomicts was also examined. The developmental processes observed in the parental apomicts were not conserved in the examined plants and alterations occurred in the components of apomixis. One plant also exhibited adventitious embryony. The results show that other genetic factors can modify apomixis with respect to time of initiation, spatial location, and mode of developmental progression. Both the apomictic locus and the modifiers are essential for efficient penetrance of the trait in Hieracium. Some of the findings in Hieracium correspond with observations in Ranunculus and this is discussed in terms of models for apomictic development and the control of apomixis in crops.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0878
    Keywords: Lactotrophs ; Bovine pituitary ; Secretory granules ; Immunogold localisation ; Cell culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The morphological characteristics of bovine pituitary cells separated by a rapid enrichment procedure are described. Single-cell suspensions were prepared from pituitary glands of steers by use of a collagenase technique and separated by discontinuous gradient centrifugation. The separation of prolactin and growth hormone-containing cells was assessed by radioimmunoassay of hormone content and immunocytochemistry, and the distribution of fibroblasts assessed after establishing cell cultures. Morphometric analysis of the fine structure of two fractions respectively enriched and depleted in the proportion of immunocytochemically-identified lactotrophs was performed after labelling with anti-prolactin antiserum coupled to immunogold complex. Cells recovered from the higher-density fraction were more highly granulated, suggesting that this was a major characteristic determining separation. Cells labelled for prolactin could not be distinguished from unlabelled cells on the basis of their granule size range, but unlabelled cells had a significantly greater coefficient of variation. These data suggest that granule density and distribution, but not granule size per se, are useful characteristics for the identification of bovine lactotrophs.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Plant cell, tissue and organ culture 45 (1996), S. 37-41 
    ISSN: 1573-5044
    Keywords: apomixis ; aneuploidy ; anther culture ; Hieracium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Plants of reduced ploidy were derived from anther tissue of a pentaploid, apomictic biotype of Hieracium pilosella (mouse-ear hawkweed). Callusing was observed from both the somatic and generative tissue of the anther. Capitulum diameter was used as a correlative character to determine the best stage for harvesting the tissue. The highest degree of callusing coincided with the early uninucleate stage of microsporogenesis. Regenerants included tetraploids, triploids and two classes of aneuploids. Segregation for apomixis was observed among the tetraploid regenerants, an indication of the dominant inheritance of apomixis in this species.
    Type of Medium: Electronic Resource
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