Elemental composition of polyphosphate bodies in aluminum-treated Pisolithus tinctorius: Comparison of chemical and freeze-substitution methods

Abstract

The toxic effects of aluminum (Al) ions on plants growing in acidic soils may be ameliorated by mycorrhizal (M) fungi, which form symbiotic associations with roots of many forest trees. Pisolithus tinctorius, a M fungus found in many acid soils, is tolerant of high levels of Al. It is not known, however, if Al is excluded from the hyphae or compartmentalized within specific organelles or areas of the hyphae. Many M fungi have been shown to accumulate divalent cations, especially Ca, with P in polyphosphate (polyP) bodies. Whether Al ions might also be localized in polyP bodies is unclear. Previously, most ion localization studies in M fungi have been performed using conventional chemical fixation (CF) methods. However, ion movement due to aqueous fixation has been demonstrated. The inhibition of ion movement during fixation is a superior feature of specimen preparation by rapid freezing followed by freeze substitution (FS). The purpose of this study was to determine by energy dispersive X-ray microanalysis (EDS) of ultrathin sections the elemental composition of polyP bodies and other hyphal areas in P. tinctorius grown at different Al levels and prepared by CF or FS methods.