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  • 1
    ISSN: 1615-6102
    Keywords: Fungus ; Meiosis ; Physoderma ; Sporangium germination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The structural and developmental characteristics of the resting sporangium in uniflagellate phycomycetes, together with the type of zoospore, are of high taxonomic value. Among these fungi, however, only a few electron microscopic investigations have been published on this topic, mainly due to technical problems. In the present study ofPhysoderma maydis (Blastocladiales) these problems were overcome as the resting sporangia in this species are formed synchronously, in large numbers, the germination is readily induced and the impermeability of the resting sporangium wall can be circumvented by shaking the prefixed sporangia with glass beads. The germination of the resting sporangia ofP. maydis is described by correlative light and electron microscopic studies and discussed in relation to related investigations on sporogenesis: The germination process starts by a breakdown of large electron-dense accretions found in the resting stage. Simultaneously, the peripheral location of the lipid bodies is lost. The large operculum is pushed open by a protrusion of the inner sporangial wall; an additional wall layer is formed during this process. Synaptonemal complexes are found in the nuclei at this stage, as are nuclear division figures which suggests anEuallomyces type of life cycle for this fungus. Cleavage vesicles, formed from dictyosomes or endoplasmic reticulum, ultimately separate the sporangial content into meiospores. The sequential assembly of organelles into the side body complex is described. Sequestering of the ribosomes into a nuclear cap is interpreted as taking place immediately prior to zoospore discharge.
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  • 2
    ISSN: 1615-6102
    Keywords: Fungus ; Parasite ; Potato ; Potato wart disease ; Synchytrium ; Zoosporangium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary An ultrastructural study of zoosporangium development ofSynchytrium, endobioticum (Schilb.) Perc. is presented. Emphasis is placed on the location of the parasitic fungal thallus in the potato host cell, on the specific location of organelles in relation to the developing zoosporangial wall, and on the host cell reaction to the fungal infection. The cytoplasmic organization of the individual sporangia after division of the zoosporangium into a sorus of sporangia is characterized by numerous similarly sized nuclei, well developed dictyosomes, and the presence of many lipid bodies of variable size. Cytoplasmic microtubules are observed to flare out from the functional kinetosome both before and after zoospore cleavage. The ultrastructural details of zoosporangium development are used to revaluate the life cycle ofS. endobioticum as described from light microscopic observations made early in the century (Curtis 1921;Köhler 1923, 1932;Percival 1910).
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 106 (1981), S. 69-82 
    ISSN: 1615-6102
    Keywords: Fungus ; Parasite ; Potato wart disease ; Resting sporangia ; Synchytrium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The cytoplasmic organization of the long-lived, thick walled resting stage of the sporangium ofSynchytrium endobioticum (Schilb.) Perc. is described. The cytoplasm of the resting sporangium contains a large number of closely packed lipid bodies and irregular electron dense bodies, which are interspaced with fine channels of cytoplasm. These ultrastructural observations are discussed in relation to the hypothesis ofBally (1912) andCurtis (1921) that zoospore primordia are already present during the resting stage. It is shown that the “zoospore primordium” is actually a lipid body and an osmiophilic body and the strands postulated to connect the individual “zoospore primordia” are actually the fine channels of cytoplasm. A new inner wall layer is laid down prior to the start of the germination. It is this wall layer which will protrude to form the vesicle in which sporogenesis takes place. The germination process observed, protrusion of a vesicle through a crack in the sporangial wall, the migration of the sporangial content into the vesicle, and the formation of a single, membrane-bound sporangium within this vesicle, is in full agreement with the recent light microscopic studies ofSharma andCammack (1976). These observations support the transfer ofS. endobioticum from the subgenusMesochytrium to the subgenusMicrosynchytrium (bothsensu Karling 1964). A major objective of the study, to obtain ultrastructural evidence for the location of the meiotic divisions in the life cycle, was not fulfilled. Three different fungi were observed to parasitize the resting sporangium ofS. endobioticum. These infections are discussed in relation to other mycoparasites of plant pathogenic fungi. The possibility of using a mycoparasite for the biological control of potato wart disease is considered to be without practical relevance.
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  • 4
    ISSN: 1615-6102
    Keywords: Fungus ; Parasite ; Potato ; Potato wart disease ; Resting sporangium ; Synchytrium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary An ultrastructural study of the development of the resting sporangium ofSynchytrium endobioticum (Schilb.) Perc. infecting potato cells is presented. The resting sporangium is found to have a single large, centrally placed nucleus with a prominent nucleolus through its entirein situ development. The cytoplasmic organization of the resting sporangium is further characterized by numerous membrane-bound lipid bodies and osmiophilic bodies. The latter have a characteristic sieve-like appearance, probably because certain storage components have been extracted during preparation for electron microscopy. Because of the similar location and appearance of these osmiophilic bodies it is suggested that they are identical to what has earlier (based on light microscopy) been described as chromatin granules; and the ultrastructural studies presented here show that “nucleolar discharge” which was described from light microscopic observations as leading to chromatin granules in the cytoplasm, and finally forming the nuclei of the zoospores (bally 1912,curtis 1921,percival 1910) simply does not occur. The appearance of dense fibrillar-like structures on the sporangial surface at an early stage of resting sporangium development ultrastructurally distinguishes the resting sporangium from the zoosporangium. The development of the layered portion of the thick sporangial wall is shown to be due to the fusion of vacuoles containing pre-made wall fibrils with the cell membrane. It is suggested that the inner compact wall layer which is essentially substructureless is formed by the membrane itself. The characteristic “wings” of the matureS. endobioticum resting sporangium originate from the potato host cell wall. Remnants of host cell organelles in the outermost layer of the resting sporangium wall show that degradation of the host cell cytoplasm contributes to wall formation of the parasite.
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  • 5
    ISSN: 1615-6102
    Keywords: Fungus ; Physoderma ; Rhizomycelium ; Sporangium development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The endobiotic thallus ofPhysoderma maydis is characterized by the presence of an extremely fine rhizomycelium which passes through the host cell wall, allowing the spread of the disease, and irregularly shaped “turbinate cells”, which may be septate or nonseptate and which are in close association with developing resting sporangia. The formation of the resting sporangium wall is first seen as localized depositions on the rounded surface of the sporangium and only later on the flattened surface of the sporangium which will form the operculum. The substructure of the resting sporangium wall is typical for members of theBlastocladiales. The resting sporangium is contiguous with the rhizomycelium during development and is finally sealed-off from the rhizomycelium by a further deposition of wall material. After the sealing-off of the resting sporangium from the rhizomycelium the content of the sporangium is compartmentalized and the two inner wall layers are deposited. The centre of the sporangium is filled with an electron dense accretion. At the periphery of the sporangium is a layer of lipid bodies. Between the lipid bodies and the central electron dense accretion is a thin layer of cytoplasm which contains the nuclei. The outer surface of the resting sporangium is smooth.
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