open access

https://hdl.handle.net/2115/35153

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

英語

acidic vacuole

2001-03

Blackwell publishing

New Phytologist

149(3)

555-563

Exopolyphosphatase activity and vacuolar acidity were assessed in order to have an overview of regulation of polyphosphate metabolism in arbuscular mycorrhizal symbiosis. Marigold (Tagetes patula) was inoculated with Glomus coronatum or G. etunicatum and grown in a mesh bag system. The extraradical hyphae were harvested from outside the mesh bag and the intraradical hyphae were collected from the mycorrhizal roots after enzymic digestion. Exopolyphosphatase activity was measured at pH 7.5 and 5.0. The extra- and intraradical hyphae of G. coronatum showed activity at pH 7.5 and 5.0, respectively. The extraradical hyphae of G. etunicatum showed activity both at pH 7.5 and 5.0, whereas intraradical hyphae of this fungus showed activity only at pH 5.0. The neutral (pH 7.5) activity showed lower Km with long-chain polyphosphate, whereas the acidic (pH 5.0) activity showed lower Km with short-chain polyphosphate. The hyphae were stained with Neutral red, an acidic compartment probe, because a pH gradient across the tonoplast has been thought to be essential for polyphosphate accumulation in vacuoles. Both extra- and intraradical hyphae had acidic compartments which were identified as vacuoles. The inoculated plants were grown for 5 weeks with P-fertilizer (50 μM KH2PO4). P was then withheld from half of the plants, to provide low P and +P treatments. After 1 week, polyphosphate in the hyphae was stained by Toluidine blue. Polyphosphate was found in the hyphae from the +P treatment but not in the hyphae from the low P treatment. In contrast, exopolyphosphatase activity and acidity of vacuoles were relatively constant irrespective of polyphosphate status. Based upon these observations it is concluded that the fungi have at least two different exopolyphosphatase-type enzymes which are differently expressed between extra- and intraradical hyphae and that polyphosphate accumulation may be dynamically regulated by the balance between synthesis and hydrolysis.

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