title: Phosphorus effects on metabolic processes in monoxenic arbuscular mycorrhiza cultures.
abstract: The influence of external phosphorus (P) on carbon (C) allocation and metabolism as well as processes related to P metabolism was studied in monoxenic arbuscular mycorrhiza cultures of carrot (Daucus carota). Fungal hyphae of Glomus intraradices proliferated from the solid minimal medium containing the colonized roots into C-free liquid minimal medium with different P treatments. The fungus formed around three times higher biomass in P-free liquid medium than in medium with 2.5 mM inorganic P (high-P). Mycelium in the second experiment was harvested at an earlier growth stage to study metabolic processes when the mycelium was actively growing. P treatment influenced the root P content and [(13)C]glucose administered to the roots 7 d before harvest gave a negative correlation between root P content and (13)C enrichment in arbuscular mycorrhiza fungal storage lipids in the extraradical hyphae. Eighteen percent of the enriched (13)C in extraradical hyphae was recovered in the fatty acid 16:1omega5 from neutral lipids. Polyphosphate accumulated in hyphae even in P-free medium. No influence of P treatment on fungal acid phosphatase activity was observed, whereas the proportion of alkaline-phosphatase-active hyphae was highest in high-P medium. We demonstrated the presence of a motile tubular vacuolar system in G. intraradices. This system was rarely seen in hyphae subjected to the highest P treatment. We concluded that the direct responses of the extraradical hyphae to the P concentration in the medium are limited. The effects found in hyphae seemed instead to be related to increased availability of P to the host root.
authors.affiliation: Department of Microbial Ecology, Ecology Building, Lund University, SE-223 62 Lund, Sweden. Pal_Axel.Olsson@mbioekol.lu.se
authors.forename: Pål Axel
authors.initials: PA
authors.lastname: Olsson
authors.forename: Ingrid M
authors.initials: IM
authors.lastname: van Aarle
authors.forename: William G
authors.initials: WG
authors.lastname: Allaway
authors.forename: Anne E
authors.initials: AE
authors.lastname: Ashford
authors.forename: Hervé
authors.initials: H
authors.lastname: Rouhier
mesh_terms: D000135:Acid Phosphatase / Q000378:metabolism; D000469:Alkaline Phosphatase / Q000378:metabolism; D018533:Biomass; D002244:Carbon / Q000378:metabolism; D002247:Carbon Isotopes / Q000378:metabolism; D046508:Culture Techniques; D018552:Daucus carota / Q000254:growth & development; D005227:Fatty Acids / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D025282:Mycelium / Q000187:drug effects / Q000254:growth & development; D038821:Mycorrhizae / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D010758:Phosphorus / Q000494:pharmacology*; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development; D014617:Vacuoles / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D005227:Fatty Acids; D010758:Phosphorus; D002244:Carbon; D000469:Alkaline Phosphatase; D000135:Acid Phosphatase; D005947:Glucose