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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 75 (1970), S. 67-79 
    ISSN: 1432-072X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The primary and secondary cysts of Saprolegnia ferax and the secondary cysts of Dictyuchus sterile have a two layered wall structure, the outer layer of which bears various types of spines. These spines, and the outer wall layer are derived from preformed structures (bars) found in the cytoplasm prior to encystment. Golgi derived vesicles appear to contribute to the inner layer of the primary cyst wall of S. ferax. The outer surface of the secondary cyst walls of this species has fibrils which are not embedded in matrix material.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 6 (1986), S. 136-145 
    ISSN: 0886-1544
    Keywords: cytoplasmic movement ; microbeam ; Ca++ ; fungi ; saltatory movement ; cytoskeleton ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We have investigated the mechanisms that hyphae of the fungus Basidiobolus magnus use to accomplish bulk movement of their cytoplasm and saltatory organelle movements. When cells were irradiated with an ultraviolet microbeam, cytoplasmic contraction occurred. The posterior cytoplasm (toward the septum) always moved forward toward the irradiated area, whereas anterior cytoplasm (between the cell tip and target) never contracted back toward the site of irradiation. Thus, there is an intrinsic polarity in the cytoplasm. Irradiations also arrested saltatory movements. The effects of irradiation on both saltations and cytoplasmic movement appear to be mediated by Ca++. Chelating exogenous Ca++ before irradiation eliminated contractions and prevented the inhibition of saltations. Furthermore, the effects of irradiation could be duplicated by using the Ca++ ionophore A23187. We relate the present results to our previous report on the effects of irradiation on the cytoskeleton [McKerracher and Heath, 1986]. We conclude that two separate cytoskeletal networks exist in fungal cells, and that an actin-containing network generates bulk cytoplasmic movement.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 103 (1980), S. 205-229 
    ISSN: 1615-6102
    Keywords: Cell wall ; Cytochalasin B ; Microfibril orientation ; Microtubules
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cortical microtubule arrays in the radish root hair were analyzed from reconstructions of serial ultra-thin sections in order to test extant hypotheses concerning the role of microtubules in the deposition of oriented microfibrils of cellulose. Passing away from the tip, root hairs exhibit a transition from random to oriented deposition of microfibrils at approximately 25 μm. Along the root hair, passing back from the tip, the microtubules: a) increase in number to a plateau at 25 μm; b) change their length profiles from approximately 60% less than 1 μm long in the hair tip to approximately 40% less than 1 μm long at 60 μm; c) maintain a constant pattern of angular deviation from the long axis, which is similar to the deviation pattern of the oriented wall fibrils; d) maintain a constant (approximately 70% of tubules) close (within 50 nm) proximity to the plasma membrane (PM); e) maintain a low (approximately 20%) degree of inter-microtubule proximity (i.e., within 50 nm of one another); f) show evidence for some variable long range (〉50 nm) association. Fixation with glutaraldehyde in a complete microtubule polymerization medium (MTPM), or pretreatment with cytochalasin B cause an approximate twofold increase in 1. the proportion of long microtubules in the tip region and 2. microtubules within 50 nm of one another. Fixation in incomplete MTPM (without GTP) produces results similar to phosphate buffer controls. Alternative explanations for these results are examined. A new hypothesis accounting for microtubule involvement in oriented microfibril deposition is described.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 173 (1993), S. 23-34 
    ISSN: 1615-6102
    Keywords: Tip growth ; Actin ; Rhodamine phalloidin ; Electroporation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A dynamic population of cytoplasmic F-actin was observed with electroporated rhodamine phalloidin (RP) staining in growing hyphae ofSaprolegnia ferax. This central actin population was distinct from the fibrillar peripheral network previously described in chemically fixed hyphae in that it was diffuse, pervaded the entire cytoplasm and was most concentrated in the central cytoplasm 8.4 μm from the tip. The peripheral network did not stain with electroporated RP. The apical concentration of central cytoplasmic actin was only present in growing hyphae and developed prior to tip extension. It co-localized with the polarized distribution of mitochondria and endoplasmic reticulum in the tip, suggesting that it functions in positioning these organelles during tip growth. Within the central actin there was a consistent apical cleft which only occurred in growing hyphae and whose position predicted the direction of tip growth. This cleft was coincident with the known accumulation of apical wall vesicles, suggesting that it is either established by vesicle exclusion of the central actin network or is permeated by a portion of the in vivo unstained peripheral network. Photobleaching studies showed that in both growing and non-growing hyphae, cytoplasmic actin continually and rapidly moved from subapical regions to the tip where it accumulated. It mostly moved forward at the rate of tip growth, while some also left the tip, presumably to populate subapical regions.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 175 (1993), S. 67-74 
    ISSN: 1615-6102
    Keywords: Tip growth ; Actin ; UV microirradiation ; Apical bursting ; Saprolegnia ferax
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The cell walls of plants and fungi are thought to provide the strength required to resist turgor and thus maintain the integrity and morphology of these cells. However, during growth, walls must undergo rapid expansion which requires them to be plastic and therefore weak. In most tip-growing cells there is an apical concentration of F-actin associated with the rapidly expanding cell wall. Disruption of F-actin in the growing tips of hyphae ofSaprolegnia ferax by a localized irradiation, beginning 2–6 μm behind the apex, with actin-selective 270 nm uv light caused the hyphae to burst, suggesting that actin supports the weak apical wall against turgor pressure. Bursting was pH dependent and Ca2+ independent at neutral pH. Hyphae burst in the very tip, where the cell wall is expected to be weakest and actin is most concentrated, as opposed to the lower part of the apical taper where osmotic shock induces bursting when actin is intact. When hyphae were irradiated with a wavelength of light that is less effective at disrupting actin, growth was slowed but they failed to burst, demonstrating that bursting was most likely due to F-actin damage. We conclude that F-actin reinforces the expanding apical wall in growing hyphae and may be the prime stress bearing structure resisting turgor pressure in tip growing cells.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1615-6102
    Keywords: Actin ; Callose ; Coenocyte ; Hypha ; Membrane potential ; Oomycetes ; Wound response
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Growing hyphae of the oomyceteSaprolegnia ferax wounded by impalement with a ca. 0.2 μm diameter glass microelectrode normally respond within seconds with an apically directed cytoplasmic contraction followed by production of a plug which encases the electrode and occludes its recording of transmembrane potentials. This plug contains callose and Ca2+-associated membranes. To characterize the rapid wounding response, we disrupted specific filamentous (F) actin populations and Ca2+ regulation. Plug formation is inhibited by disruption of F-actin populations and low exogenous Ca2+ but not by inhibition of stretch-activated Ca2+ channels with Gd3+. Therefore, stretch-activated channels are not the immediate sensor. Instead, sensing may involve strain on the actin cytoskeleton which triggers the occlusion response. This wound response is qualitatively similar to the production of septa which isolate developing sporangia and seal severed hyphae, indicating the use of a normal basic cellular developmental system as a protective mechanism against environmental damage. The wound response is essential, since an inability to seal sites of mechanical damage is potentially catastrophic in acellular coenocytic organisms.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1615-6102
    Keywords: Entomophaga aulicae ; Fungi ; Mitosis ; Nucleus associated organelle ; Taxonomy ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Nuclei in protoplasts ofEntomophaga aulicae contain abundant condensed chromatin and a large central nucleolus. The metaphase spindle occupies a small eccentric area of the nucleus while the remainder of the nucleus is filled with condensed chromatin. Small portions of condensed chromatin are aligned along a broad metaphase plate and connected to the spindle poles by kinetochore microtubules. The nucleus associated organelle (NAO) is a solid barlike structure which lies at the spindle poles and is closely associated with the outer membrane of the nuclear envelope. Comparison of the nuclear characteristics ofE. aulicae with those of other members of theEntomophthorales supports the separation of theEntomophthoraceae from theBasidiobolaceae andAncylistaceae. Further comparison of details of nuclear division in theEntomophthoraceae, specifically NAO morphology, may be useful in helping to delineate evolutionary lines within the family.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 103 (1980), S. 231-240 
    ISSN: 1615-6102
    Keywords: Cytochalasin B ; Cytoplasmic streaming ; Microfilaments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Two distinguishable populations of microfilaments (mfs) can be identified in the radish root hair. Bundles of mfs are found throughout the cytoplasm, excluding the tip region of the hair. Single mfs occur only as a cortical array, specifically associated with the microtubules. Both mf populations are oriented parallel to the direction of streaming. Hairs grown in 5 μg/ml cytochalasin B (CB) exhibit site-specific differential responses to the drug in both their streaming pattern and sensitivity of their mfs. Cytochalasin B elicits the following responses: 1. cytoplasmic streaming is reduced in all regions of the hair; 2. small particles (〈1 μm in diameter) still stream, whereas large particles (〉1 μm in diameter) no longer stream but exhibit an oscillatory or rotational motion; 3. filament bundles show increasing sensitivity to CB along the length of the hair; 4. single mfs show decreasing sensitivity to CB along the hair length. The effects of CB on cytoplasmic streaming can be related to its effects on both mf populations, thus suggesting that although mf bundles are probably involved in streaming in the sub apical and basal regions of the hair, single mfs are most likely involved in generating the slower, more irregular streaming patterns exhibited in the hair tip and CB-treated hair base.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 170 (1992), S. 46-52 
    ISSN: 1615-6102
    Keywords: Cytoplasmic migration ; Tip growth ; Actin ; Calcium ; UV microirradiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Polarized tip-ward cytoplasmic contractions were induced in hyphae ofSaprolegnia ferax with ultraviolet microirradiations. These unidirectional contractions were similar in appearance and ionic requirements to those previously induced in hyphae ofBasidiobolus magnus, suggesting that the observed inherent cytoplasmic polarity is a general phenomenon. During growth the cytoplasm is continually moving forward with respect to the lateral cell wall and plasma membrane in order to maintain its position in the tip. These contractions may be an exaggerated form of this cytoplasmic migration. F-actin was most concentrated in the contracted cytoplasm, implying that it may be involved in generating the contraction. Contractions were enhanced by external Ca2+ and by irradiating the tip region which is rich in Ca2+ sequestering organelles, suggesting that flooding of the cytoplasm with Ca2+ caused the contractions. H+ did not affect contraction frequency. Neither the change in cytoplasmic consistency that preceded contraction, the contraction itself, nor the F-actin damage induced were confined to the microirradiated zone. This is in keeping with irradiation-induced damage to a network under tension or a flux of diffusible ions causing the response. Thus Ca2+ may regulate actin-myosin interactions that generate cytoplasmic migration.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 115 (1971), S. 388-395 
    ISSN: 1432-0878
    Keywords: Microtubule ; Ultrastructure ; Spindle ; Flagellum ; Subunit
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary After a specific time of glutaraldehyde-acrolein fixation, microtubule walls appear to be composed of single 6.5–7.5 nm diameter osmiophilic subunits. Variations in the duration of glutaraldehyde-acrolein and also glutaraldehyde-osmium fixation reveal a two layered wall containing osmiophilic subunits, 4.0–4.5 nm in diameter, arranged radially, in tandem. The double-layered wall is demonstrated by microdensitometer traces. These observations are discussed in relation to previously proposed models of microtubule substructure.
    Type of Medium: Electronic Resource
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