Da. Orlovich et Ae. Ashford, POLYPHOSPHATE GRANULES ARE AN ARTIFACT OF SPECIMEN PREPARATION IN THEECTOMYCORRHIZAL FUNGUS PISOLITHUS-TINCTORIUS, Protoplasma, 173(3-4), 1993, pp. 91-102
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.