Rapid accumulation of polyphosphate in extraradical hyphae of an arbuscular mycorrhizal fungus as revealed by histochemistry and a polyphosphate kinase/luciferase system

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Summary: The rate of polyphosphate accumulation in extraradical hyphae of an arbuscular mycorrhizal fungus was investigated by conventional histochemistry and a new enzymatic method using a bacterial enzyme, polyphosphate kinase. Marigold (Tagetes patula cv. Bonanza Orange) was inoculated with Archaeospora leptoticha and grown under P‐deficient conditions. Extraradical hyphae were harvested at 0, 1, 3 and 24 h after 1 mm P‐application. PolyP levels were assessed by both metachromasy of Toluidine blue O and polyphosphate kinase which converted polyP to ATP followed by the ATP‐luciferase assay. Percentage of hyphae with metachromatic granules was increased from 25 to 44% from 0 to 1 h, and a maximum of 50% was reach by 3 h. Polyphosphate content was doubled from 1 to 3 h after P‐application (4.8–10.0 mol as Pi mg−1 protein) at a rate of 46.4 ± 15.1 nmol min−1 mg−1. The rate of polyphosphate accumulation in the hyphae was surprisingly rapid as those of polyphosphate‐hyper accumulating microorganisms. The enzymatic method employed in the present study allows highly specific and sensitive assessment of polyphosphate in the mycorrhizal system.

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