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Evidence that actin reinforces the extensible hyphal apex of the oomyceteSaprolegnia ferax

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Summary

Filamentous actin in the apices of growing hyphae of the oomyceteSaprolegnia ferax is distributed such that it could compensate for weakness in the expanding apical cell wall and thus play a role in morphogenesis of the tip. The tapered extensible portion of the hyphal tip where the cell wall is plastic contains a cap of actin which differs in organization from the actin in subapical, inextensible regions of the hypha. Rapidly growing hyphae which are expected to have a longer plastic cell wall region contain longer actin caps. Furthermore, the weakest point in the hyphal apex, demonstrated by osmotic shock-induced bursting, was within the taper where the wall is plastic but never in the extreme apex where actin was most densely packed and presumably the strongest. Treatment of hyphae with cytochalasin E/dimethyl sulphoxide induced rapid changes in actin caps. Cap disruption was accompanied by transient growth rate increases, subsequent rounding and swelling of apices and a shift of osmotically induced burst points closer to the apex. These correlated changes are consistent with a role for the actin cap in tip morphogenesis. The association between regions of plasticity in the apical cell wall, the extent of the actin cap, the location of the weakest point in the apex and the effects of damage to the actin cap suggest that the cap functions to support the apex in regions where the cell wall is weak.

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Abbreviations

CE:

cytochalasin E

DMSO:

dimethyl sulphoxide

RP:

rhodamine phalloidin

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Authors and Affiliations

  1. Department of Biology, York University, 4700 Keele Street, M3J 1P3, North York, Ontario, Canada

    Sandra L. Jackson & I. Brent Heath

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  1. Sandra L. Jackson
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  2. I. Brent Heath
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Dedicated to the memory of Professor Oswald Kiermayer

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Jackson, S.L., Heath, I.B. Evidence that actin reinforces the extensible hyphal apex of the oomyceteSaprolegnia ferax . Protoplasma 157, 144–153 (1990). https://doi.org/10.1007/BF01322647

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  • DOI: https://doi.org/10.1007/BF01322647

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