| Summary: | alpha-Aminoisobutyric acid (AIB) is a nonmetabolized amino acid analogue of alanine, which at low (muM) concentrations acts as a tracer for amino acid movements. At high concentrations (mM), it competitively inhibits membrane transport and metabolism of protein amino acids and acts as a systemic translocated inhibitor of mycelial extension in fungi. AIB can control mycelial spread of the basidiomycete Serpula lacrymans, the cause of brown rot of wood in buildings. However, it is not known how effectively the inhibitor is distributed throughout the mycelium. Realistically heterogeneous microcosms, in which the fungus grew across nutritionally inert sand to colonize discrete wood resources, were used to investigate patterns of inhibition and translocation following local application of AIB. At a 0.1 M concentration, locally applied AIB caused immediate arrest of extension throughout the whole mycelium, maintained for a 6-week experimental period. The dynamics of translocation of subtoxic amounts of [1-(14)C]AIB ([(14)C]AIB) were mapped by photon-counting scintillation imaging in conjunction with destructive harvest to establish the velocity, direction, and rate of translocation and the extent of [(14)C]AIB reallocation accompanying the invasion of fresh wood. Locally applied [(14)C]AIB was distributed throughout complex mycelial networks within 2 h of application, becoming localized in growing margins by 12 h. Encounter with a fresh wood resource triggered a widespread response, causing withdrawal of [(14)C]AIB from throughout the network, accompanied by accumulation in the newly colonized wood and associated mycelium. The results are discussed in the context of nutrient dynamics in wood decomposer fungi and the mechanism of the amino acid reallocation response.
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