Polyphosphate (phytate) formation in Quercus acutissima-Scleroderma verrucosum ectomycorrhizae supplied with phosphate

Abstract

Quercus acutissima seedlings were cultivated in growth pouches, inoculated with Scleroderma verrucosum and supplied with inorganic phosphorus (Pi) to evaluate the change in P attributable to mycorrhization and to determine the anatomical localization of polyphosphate (phytate) and polysaccharide. Semithin sections were stained with metachromatic toluidine blue O (TBO) and fluoresced with acriflavine-HCl. The total P content was analyzed during the ectomycorrhizal (ECM) development stages and spherical electron-dense opaque granules were analyzed using TEM-EDS. The spherical polyphosphates (phytate) were precipitated and stained with TBO as dark variable sized granules in the vacuoles of the mantle hyphae, Hartig net and the epidermal and apical meristem cells of the ECM root. Higher levels of P and cations K, Mg, Ca, Na which indicated polyphosphate (phytate), were detected in the spherical electron-dense opaque granules in the mantle hyphae vacuoles, Hartig net and epidermal cells. The increase in phytate granules was correlated with the ECM development stages in the ECM root tip tissue. The total P content of the root tips also increased during each developmental stage, because of ECM development. The polysaccharide granules fluoresced in the apical meristem cells during the mature mantle stage. Wall ingrowth was observed in epidermal cells adjacent to Hartig net hyphae. Thus, the P acquired from the external Pi supply by the mantle hyphae was converted to polyphosphates, which were transferred initially to the epidermal cells in the host root tips that interfaced with mantle hyphae during the early mantle stage before Hartig net formation.