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  • Cytochalasin B  (2)
  • UV microirradiation  (2)
  • Cell & Developmental Biology  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    UV microirradiation implicates F-actin in reinforcing growing hyphal tips (1993)
    Springer
    Protoplasma 175 (1993), S. 67-74 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF01403285
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    UV microirradiations elicit Ca2+-dependent apex-directed cytoplasmic contractions in hyphae (1992)
    Springer
    Protoplasma 170 (1992), S. 46-52 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF01384456
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    The organization of cortical microtubule arrays in the radish root hair (1980)
    Springer
    Protoplasma 103 (1980), S. 205-229 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF01276268
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    The differential effects of cytochalasin B on microfilament populations and cytoplasmic streaming (1980)
    Springer
    Protoplasma 103 (1980), S. 231-240 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF01276269
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Polarized cytoplasmic movement and inhibition of saltations induced by calcium-mediated effects of microbeams in fungal hyphae (1986)
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 6 (1986), S. 136-145 
    Details
    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
    URL: http://dx.doi.org/10.1002/cm.970060211
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    Paper (German National Licenses)
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