Phosphate pool dynamics in the arbuscular mycorrhizal fungus Glomus intraradices studied by in vivo 31P NMR spectroscopy

Polyphosphate (polyp) is presumably central to phosphate (P) metabolism of arbuscular mycorrhizal (AM) fungi, but its synthesis, location and chain lengths are poorly characterized. Here, we applied noninvasive and nondestructive nuclear magnetic resonance (NMR) spectroscopy to obtain novel information on AM fungal polyp. In Vivo P-31 NMR spectroscopy was used to characterize polyp and other P pools in external hyphae and in mycorrhizal roots of associations between Glomus intraradices and cucumber (Cucumis sativus). A time-course study of P-starved external hyphae supplied with additional P showed that polyp appeared more rapidly than vacuolar inorganic P. These P metabolites also appeared in the roots, but later. Polyp considerably exceeded amounts of vacuolar inorganic P, where it was located in acidic, presumably vacuolar compartments, and had a short average chain length. The rapid synthesis of polyp might be important for the maintenance of effective hyphal P uptake. Our data support the hypothesis that polyp is the major P species translocated in the tubular vacuolar network, the presence of which was previously demonstrated in AM fungi.