<p>Cyanobacteria belonging to the genus <i>Nostoc</i> have the capacity to form symbiotic associations with a wide range of organisms. Diversity, specificity and cellular modifications of the symbiosis between <i>Nostoc</i> and fungi in the formation of lichens were investigated in this thesis.</p><p>The use of the tRNA<sup>Leu</sup>UAA intron as a genetic marker for the subgeneric identification of Nostoc in complex field material was developed. Lichens belonging to the genera <i>Peltigera</i> and <i>Nephroma</i> show limited variability in their <i>Nostoc</i> symbionts. The <i>in situ</i> symbiont consists of a single strainn rather than a community of different <i>Nostocs</i>, and single thalli consistently contained the same symbiont. Patterns in symbiont identity were found in geographically remote populations and the lichen species, rather than growth locality, was shown to be important for the identity of the <i>Nostoc</i> symbiont. Examination of a <i>P. aphthosa</i> photosymbiodeme revealed that one <i>Nostoc</i> has the capacity to perform the physiological roles found in both bipartite and tripartite lichens. The symbiotic association between bryophytes and <i>Nostoc</i> on the other hand exhibited a much greater variation of <i>Nostoc</i> symbionts.</p><p>Evolutionary patterns in the tRNA<sup>Leu</sup>UAA intron were analyzed and it was shown that sequence variation was caused by several processes other than random mutations. Such evolutionary processes in genetic markers are crucial to consider, especially if phylogenetic reconstructions are attempted.</p><p>Protein profiles of symbiotic and free living <i>Nostoc</i> were analyzed using 2-dimensional gel electrophoresis. One of the major proteins in the extracts from freshly isolated symbionts was partially sequenced and shown to contain a fasciclin domain. The corresponding ORF in <i>N. punctiforme</i> was homologous to symbiotically induced genes found in different symbiotic systems. </p><p>This thesis gives new perspectives on lichens and pr for further exaovides a platform for further examiniations using tools provided by modern biology.</p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:uu-1440 |
| Date | January 2001 |
| Creators | Paulsrud, Per |
| Publisher | Uppsala University, Department of Evolutionary Biology, Uppsala : Acta Universitatis Upsaliensis |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
| Relation | Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1104-232X ; 662 |
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