In the early 1990âs, Kock and co-workers discovered acetylsalicylic acid (ASA)-sensitive
oxylipins in yeasts. It was also reported that the site of production of these compounds
may serve as important targets to control fungal infections. In 2004, researchers
exposed another function for these oxylipins â they may act as lubricants during spore
release from enclosed asci. Since oxylipin production in only a limited number of
species representing Eremothecium was thus far studied, it became the aim of this
project to further extend this study and to determine the type and distribution of 3-
hydroxy (OH) oxylipins in the remaining species i.e. Eremothecium coryli, E.
cymbalariae and E. gossypii. In addition, the possible functions of these oxylipins as
well as ascospore shape and ornamentations were assessed. Finally, the antifungal
activity of ASA was also investigated in this group of important plant pathogens as well
as other yeasts. Eremothecium coryli is known to produce intriguing spindle-shaped
ascospores with long and thin whip-like appendages. In this study, ultra structural
studies using scanning electron microscopy, indicate that these appendages serve to
coil around themselves and around ascospores causing spore aggregation.
Furthermore, using immunofluoresence confocal laser scanning microscopy it was
found that hydrophobic 3-OH oxylipins cover the surfaces of these ascospores. Using
gas chromatography-mass spectrometry, only the oxylipin 3-OH 9:1 (a
monounsaturated fatty acid consisting of a hydroxyl group on carbon 3) could be
identified. Sequential digital imaging suggests that oxylipin-coated spindle-shaped
ascospores are released from enclosed asci probably by protruding through an already
disintegrating ascus wall. Using immunofluorescence microscopy and 3-OH oxylipin
specific antibodies, it was possible to map the presence of these compounds also in
other Eremothecium species. In E. cymbalariae, these oxylipins were found to cover mostly the spiky tips of narrowly triangular ascospores while in E. gossypii, oxylipins
covered the whole spindle-shaped ascospore with terminal appendages. The presence
of these oxylipins was confirmed by chemical analysis. When ASA, a 3-OH oxylipin
inhibitor, was added to these yeasts in increasing concentrations, the sexual stage was
found to be the most sensitive. Results suggest that 3-OH oxylipins, produced by
mitochondria through incomplete β-oxidation, are associated with the development of
the sexual stages in both yeasts. Strikingly, preliminary studies on yeast growth suggest
that yeasts, characterized by mainly an aerobic respiration rather than a fermentative
pathway, are more sensitive to ASA than yeasts characterized by both pathways. These
data further support the role of mitochondria in sexual as well as asexual reproduction
of yeasts and its role to serve as target for ASA antifungal action.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-09052007-141707 |
| Date | 05 September 2007 |
| Creators | Leeuw, Ntsoaki Joyce |
| Contributors | Prof PWJ van Wyk, Dr CH Pohl, Prof JLF Kock |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-09052007-141707/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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