Bibliographic Detail
Beck, A., 2002
Reference:
Beck, A. (2002). Selektivität der Symbionten schwermetalltoleranter Flechten Dissertation zur Erlangung des Doktorgrades der Fakultät für Biologie der
Ludwig-Maximilians-Universität München. pp. [1]-194, 74 figs. Kirchheim: Offsetdruck Fischer GmbH.
Publication Date:
"November 2002"
Location:
Kirchheim
Notes:
ISBN: 3-9808102–0-8. Art. 30.9 states "Note 3. The presence of an International Standard Book Number (ISBN) or a statement of the name of the printer, publisher, or distributor in the original printed version is regarded as internal evidence that the work was intended to be effectively published."
Abstract:
The selectivity of lichen symbionts growing on heavy-metal-rich substrate was investigated and the phylogenetic relationship of the photobionts was analysed in detail by light microscopical observation of axenically cultured algal clones as well as by molecular characterisation (nrDNA sequence analysis) of selected clones. Photobionts of the same lichen species not growing on heavy-metal-rich substrate were investigated to study the influence of the substrate on the selectivity of the symbionts. In addition, physiological experiments focussing on the heavy metal tolerance of lichen algae were conducted. The spectrum of photobionts in the investigated lichen communities was analysed with respect to geography, reproduction strategies of the lichens and phylogenetic position of the mycobionts. - Twelve species from five genera of the Trebouxiophyeae T.FRIEDL (1995) were shown to be the photobionts of the 62 investigated lichen species: Apatococcus lobatus, Asterochloris irregularis, A. magna, Chlorella ellipsoidea, C. saccharophila, Coccomyxa spec., Trebouxia angustilobata (A.BECK) A.BECK comb. nov., T. australis A.BECK spec. nov., T. brindabellae A.BECK spec. nov., T. incrustata, T. simplex and T. suecica A.BECK spec. nov. The photobionts of 56 lichen species were investigated for the first time. During the study 1625 algal clones from 176 lichen samples were analysed. The assignment of the photobionts to the lichen species can be seen in tables 12 to 19. - Three species of the genus Trebouxia (T. australis, T. brindabellae and T. suecica) were described as new to science based on morphological and ITS nrDNAsequence peculiarities, a subspecies of T. jamesii was treated as a new species (T. angustilobata). - The common soil algae Apatococcus lobatus (only uncertain reports) and Chlorella saccharophila were recognized to be lichen photobionts for the first time. - Molecular analysis of 113 ITS nrDNA sequences confirmed the morphological observations and allowed a more detailed differentiation between the isolated photobiont clones. - The genus Trebouxia can be divided into four groups, the phylogenetic relationship of which remained unclear. Each group comprises several, morphological distinct, species. The photobionts of lichens from heavy-metal-rich substrate belonged to group 1 (T. arboricola-group) and 4 (T. simplex-group). - To investigate correlated base changes in conserved regions of ITS2 for the differentiation of species, the distribution of base changes was mapped on the ITS2 nrDNA secondary structure. This character, however, can not be used for the differentiation of species in the genus Trebouxia. - The analysis of the 1512-introns in the 18S nrDNA of 44 photobiont clones allowed a further characterisation of the photobiont clones, because within a group of clones with homogenous ITS nrDNA sequence (T. simplex [gt A]) five different 1512 intron sequences were found. Due to differences in the ITS nrDNA and 1512 intron sequence phylogeny it could be concluded, that the intron of T. australis has been aquired by horizontal gen-transfer. - Almost all lichens exhibited a pronounced selectivity of photobiont choice, only algae of one of the four groups of Trebouxia were acceptable photobionts. Which clone within that group was selected as photobiont did not depend on the phylogenetic position of the mycobiont but on the locality – and therefore on climatic and geographic factors. Cospeciation was therefore not observed. - The occurrence of photobionts in the families Lecideaceae and Porpidiaceae is noteworthy. Based on the analysis of 10 new 18S nrDNA sequences of mycobionts it could be shown, that both families form a monophyletic group in the Lecanorales. Neverthless only species without a Lugol reaction in the medulla were lichenised with Asterochloris, whereas the species with Lugol reaction in the medulla were lichenised with Trebouxia or Chlorella. This is the first known example of a correlation between a morphological-chemical character of the mycobiont and its photobiont choice within a monophyletic group of lichens. - The photobionts differed in their heavy-metal resistance, most notably with respect to copper. Trebouxia simplex [gt A] (AB97.017A2) tolerated the highest copper concentrations, a clone of Trebouxia jamesii (UTEX 2233) was the most sensitive. These results correlated with the copper concentration in the substrate of the lichens. - Using SH-group specific HPLC-analysis phytochelatin production could be detected in all clones (UTEX 2233, AB97.070B2 and AB97.017A2) during Cd challenge. These phytochelatins were ligands for the cadmium and a complex between these compounds could be demonstrated using gel-filtration. - The finding of genetically very similar photobionts in lichens growing on substrates with and without heavy-metals argues against an influence of the heavy-metals in the substrate on the photobiont choice of the mycobiont. In cases where the heavy metal content of the substrate was very high, the lichens with the less tolerant photobiont were lacking (e.g. Porpidia macrocarpa), but did not change their photobiont.
