EFFLUX OF PHOSPHATE FROM THE ECTOMYCORRHIZAL BASIDIOMYCETE PISOLITHUS-TINCTORIUS - GENERAL-CHARACTERISTICS AND THE INFLUENCE OF INTRACELLULAR PHOSPHORUS CONCENTRATION

We have investigated phosphate absorption and efflux from mycelium of Pisolithus tinctorius and compared this with several other ecto- and ericoid mycorrhizal fungi. Phosphate absorption over a 16 h period was similar in all fungi (19-38 mu mol g(-1) D.W.) with the exception of Paxillius involutus where absorption was 2-4 times greater. Efflux of phosphate from Pisolithus tinctorius followed the established pattern for efflux of ions from plant and fungal tissue. The proportion of P-32 absorbed that was lost to the bathing solution during an 8 h elution period was around 10% for all fungi. Efflux of phosphate from P. tinctorius was greatest and absorption lowest where the fungus had a high intracellular phosphorus concentration. It is suggested that efflux of phosphate may be important in regulating mycelial phosphorus balance where mycelium has a high phosphorus status, with net efflux occurring where the intracellular orthophosphate concentration is high and the external phosphate concentration is low. The results are discussed in the context of nutrient transfer at the fungus-root interface in ectomycorrhizas.