Colour changes with chemicals

A large number of different chemicals are used as taxonomic aids in mycology (Meixner, 1975; Singer, 1986). Because macrochemical reac tions can help in the identification of fruit bodies, it was assumed that ectomycorrhiza, too, would show specific reactions (Trappe, 1967; Zak, 1973; Agerer, 1986a). However, only a few chemicals have so far been successfully applied to ectomycorrhiza.

Perhaps the most important chemical is Melzer's reagent. Parts of some ectomycorrhiza stain blue in this reagent, producing what is called an amyloid reaction (Chroogomphus: Miller, 1983; Agerer, 1990a; Endogone lactiflua: Walker, 1985; Gomphidius: Agerer, 1991a; Thele-phora terrestris: Agerer, 1991a). Some hyphae of Gomphidius spp. are stained slightly brownish (Agerer, 1991a), a so-called dextrinoid reaction. Furthermore, this reagent is able to reveal what are possibly parasitic hyphae of the genera Chroogomphus and Gomphidius within ectomycorrhiza of Suillus and Rhizopogon spp. (Agerer, 1990a, 1991a). Sulfovanillin can be used to stain the laticifers of Lactarius ectomycorrhiza red or blue or almost black (Peyronel, 1934; Agerer, 1986b; Brand and Agerer, 1986; Agerer et al., 1990) and the outer mantle cells of Lactarius spp. of the section Plinthogali (e.g. Lactarius picinus: Agerer et al., 1990) or the special cells of the mantle surface of some Russula spp. (e.g. Russula emetica: Agerer et al., 1990; Brand, 1991). The whole mantle can also be stained a distinctly violet colour with sulfovanillin (e.g. Hygrophorus lucorum: Treu, 1990a). Toluidine blue is utilized by Ingleby et al. (1990) because it displays metachromatic reactions of the hyphal walls. They can become purple, violet or pink. Potassium hydroxide (KOH) stains some ectomycorrhiza brown (e.g. Tricholoma flavobrunneum: Uhl, 1988a) or brownish red (Leccinum spp.: Müller and Agerer, 1990a). The cell mounds of Russula ochroleuca stain red (Brand, 1991). The colour change, at least in Leccinum and Russula ochroleuca, is reversible by acids (Müller and Agerer, 1990a; Brand 1991). Further species turn to violet (e.g. Cortinarius cinnabarinus: Brand, 1991). Ethanol is useful as an extractant of pigments from ectomycorrhiza (e.g. Dermocybe: Thoen, 1977).

Other reagents cause irregular reactions or have only been used infrequently: Sudan III stained some cystidial contents red (Fagirhiza globulifera: Brand, 1991); guaiacol stained ectomycorrhiza of Tricholoma vaccinium blue (Agerer, 1987d); ectomycorrhizal mantles of Tuber macrosporum are stained brown in FeS04 (Giovanenetti and Fontana, 1981); ectomycorrhiza of Lactarius obscuratus were stained violet by pyrogallol and green by concentrated NH4OH (Froidevaux, 1973); and the addition of weak acids (lactic acid) to Leccinum ectomycorrhiza, which had turned blue after lying for some time in water, can change the blue colour to red (Müller and Agerer, 1990a).

There is a need to continue the search for additional chemicals which can cause colour changes. In spite of some disappointing results up to now with some chemicals (Agerer, 1987b), the above-mentioned results show that chemical reagents can contribute to the successful characterization of ectomycorrhiza.

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