Reciprocal Translocation of Carbohydrates Between Host and Fungus in Bahiagrass Infected withMyriogenospora atramentosa

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Abstract
The pathogen M. atramentosa provides an unprecedented model for the study of fungal biotrophy. Both mycelium and stromata of the fungus were entirely epiphytic upon the leaf blades of the host grasses Paspalum notatum and Andropogon virginicus, and both host and pathogen could be separated along their interface into separate homogeneous fractions for analysis. Successive opposing leaves of the host were commonly bound together at the tips by bridges of fungal stromata. Infected leaves contained less than 4% of the sucrose present in uninfected leaves. The primary carbohydrates present in stromatic extracts were the sugar alcohols mannitol and arabitol. An unidentified low-molecular-weight compound present in extracts of uninfected leaves and stromata was absent from extracts of infected leaves. Greater amounts of 14C label (originally supplied as 14CO2) accumulated in compounds in infected leaves than in uninfected leaves. Compounds containing 14C label originally supplied as 14C-sucrose moved from leaf to stromatic bridge to second leaf. Although microscopy showed no alteration of the cuticle separating host and fungus, host epidermal cells beneath the fungus were modified in size and shape.