Interaction Chemistry Enzyme Production

During decomposition, basidiomycetes release many different enzymes (Chapter 2), and there is considerable evidence to suggest a role for up- and down-regulation of particular enzyme groups during fungal-fungal interactions. As with many aspects of interactions, the environmental conditions used during assay can greatly influence up- or down-regulation during experiments (Freitag and Morrell, 1992; White and Boddy, 1992; Lang et al., 1997). Enzymatic production of reactive oxygen species, phenoloxidases and sometimes ^-glucosidase increases (Freitag and Morrell, 1992; White and Boddy, 1992; Lang et al., 1997; Iakovlev and Stenlid, 2000; Iakovlev et al., 2003; Baldrian, 2006). Laccase enzymes appear to increase in contact zones between interacting decay-causing species (White and Boddy, 1992), with different temporal effects depending on the species tested (Iakovlev and Stenlid, 2000). Induction of the laccase response was elicited in Marasmiellus troyanus by cell-free filtrates of Marasmius pallescens, both tropical wood-decomposing basidiomycetes (Ferreira Gregorio et al., 2006), and was accompanied by a concomitant increase in activity of a second group of lignin degrading enzymes—the manganese-dependent lignin peroxidases. Laccase activities also increased in cultures of Trametes versicolor and Pleurotus ostreatus following challenge with soil microorganisms, including fungi, bacteria and soil or soil extracts (Baldrian, 2004). Laccase does not directly affect decay fungi (Baldrian, 2004); its role is probably defensive, being involved in the production of melanins and similar compounds (Eggert et al., 1995; Baldrian, 2006) which frequently accompany interspecific interactions, although this hypothesis requires further testing.

Fungal chitinases may also play a role in interspecific interactions. Wood decay-causing fungi with secondary resource capture strategies may produce chitinases during the colonization process, causing cell lysis and, therefore, releasing sequestered nitrogen from the thalli of previous colonizers (Lindahl and Finlay, 2006).

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