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Ultrastructure of chytridiomycete and oomycete zoospores using spray-freeze fixation

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Summary

The ultrastructure of zoospores of several zoosporic fungi was examined using a modified cryofixation technique. An atomizer was used to spray a zoospore suspension into the cold propane reservoir of a conventional plunge freeze-substitution apparatus. Spray-freeze fixation and freeze-substitution of zoospores porvided better fixation of vacuolar structures, membranes and the extracellular coat than that obtained with chemical fixation. The overall shape of cryofixed spores was closer to that seen in living zoospores. Two types of vacuoles were seen in cryofixed zoospores ofMonoblepharella andChytridium. One type of vacuole contained electron-opaque material within the lumen while the other type had no visible internal material in the lumen and appeared to be part of the water expulsion vacuole complex. Coated pits and coated vesicles were observed associated with both the water expulsion vacuoles and the plasma membrane inMonoblepharella andPhytophthora, suggesting that endocytosis of the plasma membrane and expulsion vacuoles is part of membrane recycling during osmoregulatory events. An extracellular coat was seen on the outer surface of cryofixed zoospores ofMonoblepharella sp.,Chytridium confervae andPhytophthora palmivora without the use of carbohydrate-specific stains. The spray-freeze method gave good and reproducible fixation of the wall-less spores in quantities greater than those obtained in previously described zoospore cryofixation studies. The technique is potentially useful for cell suspensions in that freeze damage from excess water is limited.

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Abbreviations

ddH2O:

deionized distilled water

PME:

Pipes/MgCl2/EGTA buffer

WEV:

water expulsion vacuole

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  1. Department of Botany, University of Georgia, 2502 Miller Plant Science Building, 30602-7271, Athens, GA, USA

    John P. Shields & Melvin S. Fuller

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  1. John P. Shields
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  2. Melvin S. Fuller
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Shields, J.P., Fuller, M.S. Ultrastructure of chytridiomycete and oomycete zoospores using spray-freeze fixation. Protoplasma 191, 84–95 (1996). https://doi.org/10.1007/BF01280828

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  • DOI: https://doi.org/10.1007/BF01280828

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