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Polarized cytoplasmic movement and inhibition of saltations induced by calcium-mediated effects of microbeams in fungal hyphae (1986)

McKerracher, L. J. ; Heath, I. B.

New York, NY : Wiley-Blackwell

Cell Motility and the Cytoskeleton 6 (1986), S. 136-145

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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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UV microirradiation implicates F-actin in reinforcing growing hyphal tips (1993)

Jackson, Sandra L. ; Heath, I. B.

Springer

Protoplasma 175 (1993), S. 67-74

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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.