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Rapid wound responses ofSaprolegnia ferax hyphae depend upon actin and Ca2+-involving deposition of callose plugs (2000)

Levina, N. N. ; Heath, I. B. ; Lew, R. R.

Springer

Protoplasma 214 (2000), S. 199-209

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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

URL: http://dx.doi.org/10.1007/BF01279064

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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.