Preparative Techniques for Transmission Electron Microscopy and Confocal Láser Scanning Microscopy of Lichens

Transmission electrón microscopy. Ultrastructural study of lichen symbionts can provide valuable information about symbiotic performance complementary to that obtained using other techniques (Lallemant et al. 1986). Transmission Electron Microscopy (TEM) was first used to describe the cellular organelles of both symbionts (Jacobs and Ahmadjian 1969; Boissiére 1972; Galun et al. 1970,1974; Peveling 1973, 1974, 1976; Ascaso and Calvan 1975, 1976). Later, different aspects of lichen symbiosis were studied, for example cellular membranes and cell wall with the freeze-etching electrón microscopy technique (Ellis and Brown 1972; Peveling and Robenek 1980; Ascaso et al. 1985; Honegger 1986a; Rapsch et al. 1986). TEM has contributed to the understanding of different types of mycobiont-photobiont relationships in lichens, e.g. by observing the physical contacts between symbionts (for reviews see Honegger 1984, 1985, 1986b). The study of storage bodies in both symbionts provides indirect information on biotrophic relationships (Valladares and Ascaso 1994). Some authors have described the variability of lichen ultrastructure in relation to season or environment (Holopainen 1982; Scott and Larson 1986; Fiechter and Honegger 1988; Balaguer et al. 1999). In some investigations, TEM techniques have revealed structural changes due to different experimental conditions, ranging from desiccation to environmental pollution (Eversman and Sigal 1984, 1987; Ascaso et al. 1986, 1988; Brown et al. 1987, 1988; Balaguer et al. 1996, 1997; Tarhanen et al. 1997).