Phosphate pool dynamics in the arbuscular mycorrhizal fungus Glomus intraradices studied by in vivo³¹P NMR spectroscopy

Abstract

Summary• 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 31 P 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.

pH measurement of tubular vacuoles of an arbuscular mycorrhizal fungus, Gigaspora margarita

“…Cytochemical and biochemical reports have described that AM fungi also synthesize polyphosphate and accumulate it in tubular vacuoles (Cox et al 1980;Kuga et al 2008;Tani et al 2009). The vacuoles in which polyphosphate accumulates have pH 6.0, as indicated by the chemical shift of terminal phosphate residues in the polyphosphate chain by in vivo 31 P-NMR spectroscopy (Viereck et al 2004), which is consistent with our pH measurement of tubular vacuoles. In the mildly acidic condition of the tubular vacuoles, it was inferred that polyphosphate is partially charged and that it exists in soluble form because acid dissociation constants of polyphosphate (16 residues) are 5-6.5 (MacDonald and Mazurek 1987).…”

“…The vacuolar pH (mean pH of 5.6) measured using CFDA was consistent with pH in a putative vacuolar compartment estimated from a chemical shift value of P i signal by in vivo 31 P-NMR analysis of G. intraradices, showing pH 5.6 (Rasmussen et al 2000) and 5.5 (Viereck et al 2004). In yeast S. cerevisiae, vacuolar pH was found to be 6.2 (Preston et al 1989) and 6.5 (Makarow and Nevalainen 1987) based on pH-dependence of fluorescent probes.…”

“…Similarly, pH of tubular vacuole systems of EM fungus Pisolithus tinctorius have mild acidity, whereas the vacuolar pH exhibited widely varied pH of 4.3-7.5 based on ratio imaging of 6-carboxyfluorescein (CF)-loaded vacuoles (Rost et al 1995). Using 31 P-NMR spectroscopy, acidic compartments of extraradical hyphae in AM fungus G. intraradices were estimated as pH 6.0 based on the chemical shift of terminal phosphate residues in the polyphosphate chain (Viereck et al 2004). This result might indicate the acidity of tubular vacuoles in AM fungi, but limitations exist in spatial resolution of NMR spectroscopy in distinguishing individual tubular vacuoles of AM fungi.…”

Effects of the mycorrhizal fungus Glomus intraradices on uranium uptake and accumulation by Medicago truncatula L. from uranium-contaminated soil

“…When only hyphae could grow into C B , P contents in roots in C A were significantly higher than when there was root access to P in C B . This indicates that hyphae could not only efficiently take up P (Li et al, 1991;Rufyikiri et al, 2004a), but also efficiently transfer P to host plants (Viereck et al, 2004).…”

The Role of the Mycorrhizal Symbiosis in Nutrient Uptake of Plants and the Regulatory Mechanisms Underlying These Transport Processes

“…Two types of polyP can be distinguished in mycorrhizal fungi: short chain polyP with a length of up to 20 Pi residues and long chained polyP with more than 20 Pi residues. The average length of short chained polyP in AM fungi has been estimated as 11-20 Pi [78,79], and of long chained polyP as 190 to 300 Pi residues [80,81]. Mycorrhizal fungi can rapidly store a significant proportion (more than 60%) of their cellular P as polyP [69,82,83].…”