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

Summary • Regulation of polyphosphate metabolism is reported in arbuscular mycorrhizal symbiosis. • Marigold (Tagetes patula) plants inoculated with Glomus coronatum or Glomus etunicatum were grown in mesh bags. Exopolyphosphatase activity in extra‐ and intraradical hyphae was measured and characterized. The hyphae were stained with Neutral red to show acidic vacuoles in which polyphosphate synthesis might occur. • Exopolyphosphate activity was differently expressed between the extra‐ and intraradical hyphae, as indicated by different pH optima; high activity was observed at pH 5.0 in the intraradical hyphae of both fungal species. Km values were lower at neutral pH with long‐chain polyphosphate, whereas acidic activity showed lower Km with short‐chain polyphosphate. Both extra‐ and intradical hyphae had acidic vacuoles. Polyphosphate occurred in the hyphae of the high‐P, but not the low‐P treatment. By contrast, exopolyphosphatase activity and vacuolar acidity were relatively constant irrespective of polyphosphate status. • The fungi have at least two different exopolyphosphatase‐type enzymes which are differently expressed between extra‐ and intraradical hyphae; polyphosphate accumulation might be a dynamic balance between synthesis and hydrolysis.