Measuring Ergosterol and Chitin in Lichens
Mycobiont biomass dominates in most lichen thalli, and it is generally believed that the fungus acts as a major sink for carbon assimilated by the photobiont, and even nitrogen in cyanobacterial lichens (Rai 1988 , Fahselt 1994 ). However, fungal metaboli
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Measuring Ergosterol and Chitin in lichens LENA DAHLMAN, MARGARETA ZETHERSTROM, BODIL SUNDBERG, TORGNY NXSHOLM, and KRISTIN PALMQVIST
Introduction Mycobiont biomass dominates in most lichen thalli, and it is generally believed that the fungus acts as a major sink for carbon assimilated by the photobiont, and even nitrogen in cyanobacterial lichens (Rai 1988, Fahselt 1994). However, fungal metabolism within lichens has been poorly studied, and so far there are no studies where fungal respiration, energy or metabolite demand has been separated from photobiont requirements. Even though it has been firmly established that export of assimilates from photo- to mycobiont may be extensive (Richardson and Smith 1966, Tapper 1981, Lines et al. 1989), quantitative measures of carbon and nitrogen distribution patterns between the symbionts of lichens are largely lacking. One important part of such studies would be to find unique cellular components of the myco- and photobiont, that can be related either to their respective metabolism or to their biomass. Possible fungal markers
There are some prominent components of lichens and fungi that can be used as such markers, namely chlorophyll for the photobiont, and chitin as well as ergosterol for the fungus. Ergosterol is the principal sterol of fungal plasma membranes (cf. Griffin 1994 and references therein) and it has Lena Dahlman, Umea University, Department of Ecology and Environmental Science, Umea, 901 87, Sweden Margareta Zetherstriim, Swedish University of Agricultural Sciences, Department of Forest Genetics and Plant Physiology, Umea, 901 83, Sweden Bodil Sundberg, Umea University, Department of Plant Physiology, Umea, 901 87, Sweden Torgny Nasholm, Swedish University of Agricultural Sciences, Department of Forest Genetics and Plant Physiology, Umea, 901 83, Sweden ~ Kristin Palmqvist, Umea University, Department of Ecology and Environmental Science, Umea, 901 87, Sweden (phone + 46-90-7869184; fax +46-90-7866705; e-mail [email protected])
I. C. Kranner et al. (eds .), Protocols in Lichenology © Springer-Verlag Berlin Heidelberg 2002
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been demonstrated that this component is also well correlated with basal respiration rates of lichens (Sundberg et al. 1999). However, it is possible that ergosterol may also be a constituent of some lichen photobionts (Goodwin, 1974), so further studies are needed to resolve whether ergosterol is unique for the fungus. Chitin is the beta (1-4)-linked polymer ofN-acetyl-glucosamine, being a cell wall component of most fungi (cf. Griffin 1994). Chitin is synthesised vectorially through the fungal plasma membrane by a transmembrane synthase. This synthase accepts glucosamine precursors from the cytosol, feeding and polymerizing them through the plasma membrane and into the wall (Gooday 1995). Depending on the fungal species, chitin content in relation to other cell wall compounds is highly variable (cf. Griffin 1994), and at least among lichens it appears that chitin c
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