This thesis described the experimental analysis of several aspects of multicellular development in <I>Sordaria brevicollis</I>, a filamentous ascomycete which has previously been considered to be exclusively heterothallic. Sexual reproduction in <I>S. brevicollis</I> requires the formation of protoperithecia, which must usually be crossed by fertilisation with spermatia of the opposite mating type before perithecial development can take place. The morphology of protoperithecia and crossed perithecia has been examined using a variety of microscopical techniques. Also described is the formation of two additional types of multicellular structure, which have not been characterised previously, uncrossed perithecia, and vegetative hyphal aggregates (VHAs). Uncrossed perithecia are produced by homokaryons of both mating types, although the phenomenon is more commonly observed in strains of <I>mt</I>A. The term is used to cover a number developmental stages, which range from enlarged protoperithecia, that form ostioles but exhibit no further differentiation, to perithecia which develop (at least) rudimentary necks. Although the majority of uncrossed perithecia are empty, a proportion of the fruitbodies which develop on <I>mt</I>A homokaryons have been found to contain a few ascospores, arranged in linear, 8 -spored asci. Homokaryotic spore production has never been observed in strains of <I>mta</I>. The genetic mechanisms underlying the development of ascospores in uncrossed perithecia have been examined using heterokaryon analysis. Heterokaryons constructed using spore colour mutants were used to show that meiosis and recombination occurred during the formation of ascospores in uncrossed perithecia, but the recombination frequency (calculated from the percentage of symmetrical M II asci) was lower than that from a comparable heterothallic cross. It was also shown that the frequency of third division overlap was significantly higher in the asci from uncrossed perithecia than in those from crossed perithecia. Observations based on homothallic and heterothallic development have been used to construct and evaluate two models for nuclear behaviour during the formation of protoperithecia. The evolution of homothallism and heterothallism in <I>Sordaria</I> and <I>Neurospora </I>has also been considered in the light of the facultative homothallism seen in <I>S. brevicollis. </I>
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:661255 |
| Date | January 1993 |
| Creators | Robertson, Susan Jane |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/12866 |
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