ORIGINAL PAPER

Mycorrhiza

, Volume 9, Issue 3, pp 137-144

Exudation-reabsorption in a mycorrhizal fungus, the dynamic interface for interaction with soil and soil microorganisms

  • Yu-Ping SunAffiliated withDepartment of Forest Mycology and Pathology, Swedish University of Agricultural Sciences, P.O. Box 7026, S-750 07 Uppsala, Sweden e-mail: torgny.unestam@mykopat.slu.se
  • , T. UnestamAffiliated withDepartment of Forest Mycology and Pathology, Swedish University of Agricultural Sciences, P.O. Box 7026, S-750 07 Uppsala, Sweden e-mail: torgny.unestam@mykopat.slu.se
  • , Steven D. LucasAffiliated withDepartment of Surgery, Uppsala University, S-751 85 Uppsala, Sweden
  • , Karl Johan JohansonAffiliated withDepartment of Radioecology, Swedish University of Agricultural Sciences, P.O. Box 7031, S-750 07 Uppsala, Sweden
  • , Lennart KenneAffiliated withDepartment of Chemistry, Swedish University of Agricultural Sciences, P.O. Box 7015, S-750 07 Uppsala, Sweden
  • , Roger FinlayAffiliated withDepartment of Forest Mycology and Pathology, Swedish University of Agricultural Sciences, P.O. Box 7026, S-750 07 Uppsala, Sweden e-mail: torgny.unestam@mykopat.slu.se

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Abstract

 The mycelium of Suillus bovinus slowly absorbed [U-14C]glucose and other tracers from droplets placed on the cords, translocated them to the peripheral hyphae and exuded them into fluid drops on the hyphal tips. The exudate was characterized by 1H NMR spectroscopy and by sugar and amino acid analysis. The exuded compounds were mainly carbohydrates and peptides. Acetic acid and oxalic acid were also present in the exudate along with a number of unidentified compounds. Released ions (K, Na, Cl, P, Mg and Ca) were identified by X-ray microanalysis. The mycelium was shown to reabsorb up to 65% of the exuded 14C compounds in 2 days. Glucose, mannitol, glutamic acid (pH 3.2), and Rb+ (as well as other mineral ions) were all readily absorbed by the mycelium, while oxalic acid at pH 4.2 and glutamic acid at pH 6.5 were not. Exudation of fluid droplets on the surface of the hydrophobic mycorrhizal fungus S. bovinus may represent an ecophysiologically important function of the extramatrical hyphae, which provides an interface for interaction with the immediate hyphal environment and its other microorganisms where the peripheral hyphae exchange their photosynthetically derived products for nutrients to be used later by the pine host. We hypothesize that actively absorbed carbohydrates from the root are translocated to the peripheral hyphae along a concentration gradient of sugars and polyols by means of active translocation and diffusion in cell elements and by acropetal water transport in the cord vessels.

Key word Exudation Reabsorption Mycelium-soil interface Osmotic gradient pump Carbon and water translocation