Immunogold labeling of an extracellular substance producing hydroxyl radicals in wood degraded by brown-rot fungus Tyromyces palustris

A fraction containing low-molecular-weight peptides that catalyzes redox reactions between electron donors and O-2 to produce OH, was partially purified from wood-decaying cultures of the brown-rot fungus Tyromyces palustris. Polyclonal antibodies raised to the fraction were used for immunogold labeling of transverse sections of sapwood of spruce in various stages of degradation by T. palustris to demonstrate the cellular localization of the OH-producing substance. Initially, the wood cell wall was attacked primarily by fungal hyphae growing in the cell lumen. During the early stages of degradation, the gold label was localized in the fungal cytoplasm and cell wall and in the extracellular slime sheath surrounding the fungal cell wall. The gold label also was found throughout the wood cell wall, although the cell wall remained almost intact so long as the fungal hyphae remained in the lumen. Thus, the OH-producing substance is secreted by the hyphae into the lumen, and it diffuses through the S3 laver into the S2 layer and the middle lamella. The role of this OH-producing system in wood degradation by T. palustris is discussed.