Differentiation of polyphosphate metabolism between the extra- and intraradical hyphae of arbuscular mycorrhizal fungi

. Regulation of polyphosphate metabolism is reported in arbuscular mycorrhi zal symbiosis. . Marigold (Tagetes patula) plants inoculated with Glomus coronatum or Glom us etunicatum were grown in mesh bags. Exopolyphosphatase activity in extra - and intraradical hyphae was measured and characterized. The hyphae were s tained with Neutral red to show acidic vacuoles in which polyphosphate synt hesis might occur. . Exopolyphosphate activity was differently expressed between the extra- an d intraradical hyphae, as indicated by different pH optima; high activity w as observed at pH 5.0 in the intraradical hyphae of both fungal species. K- m values were lower at neutral pH with long-chain polyphosphate, whereas ac idic activity showed lower K-m with short-chain polyphosphate. Both extra- and intradical hyphae had acidic vacuoles. Polyphosphate occurred in the hy phae of the high-P, but not the low-P treatment. By contrast, exopolyphosph atase activity and vacuolar acidity were relatively constant irrespective o f polyphosphate status. . The fungi have at least two different exopolyphosphatase-type enzymes whi ch are differently expressed between extra- and intraradical hyphae; polyph osphate accumulation might be a dynamic balance between synthesis and hydro lysis.