POLYPHOSPHATE GRANULES ARE AN ARTIFACT OF SPECIMEN PREPARATION IN THEECTOMYCORRHIZAL FUNGUS PISOLITHUS-TINCTORIUS

Polyphosphate granules are precipitated in the vacuoles of the ectomyc orrhizal fungus Pisolithus tinctorius (Pers.) Coker & Couch by various treatments, including conventional specimen preparation. Granules are not produced by glutaraldehyde fixation but appear at early stages of ethanol dehydration and are visible with Nomarski DIC microscopy. The y show gamma-metachromasy with toluidine blue O at low pH, are extract ed by cold trichloroacetic acid and contain phosphorus and calcium as demonstrated by X-ray microanalysis. The granules are surrounded by el ectron-lucent areas that do not contain these elements at detectable l evels. In contrast, vacuoles of freeze-substituted hyphae contain even ly dispersed flocculent material. Phosphorus and potassium are distrib uted more or less uniformly throughout, but calcium is not detected. T his indicates that polyphosphate is present in the vacuole of living h yphae in soluble form and is precipitated to form granules by various treatments. It is thought that granules form when membranes, including the tonoplast, become leaky and there is an influx of precipitating i ons such as calcium.