Nitrogen metabolism of external hyphae of the arbuscular mycorrhizal fungus Glornus intraradices

Abstract

SUMMARYThe arbuscular mycorrhizal (AM) fungus Glomus intraradices Schenck and Smith was grown in symbiosis with Cucmnis sativus L. cv. Aminex (Fl hybrid) in mesh hags surrounded by a sand-filled hyphal compartment (HC), allowing only the fungal hyphae to protrude into the HC. The hyphae in the HC were supplied with '°N-labelled NH,* or NOj" after 60 d (expt 1). Following a 48 h labelling period, the sand was removed from the HC and the hyphae extracted. In another experiment (expt 2), the hyphae were extracted from the sand before being incubated in vitro in a nutrient solution containing '""'N-labelled NH^* for 15 h. The hyphal material was incubated in a 0 or 2'5 mM solution of the GOGAT-inhibitor albizzine prior to labelling. In both experiments the hypha! content of free amino acids and fatty acids w^ere measured as well as the amino acid ^°N enrichment.Asparagine was the hyphal amino acid measured in highest concentration followed by glutamine, glutamate, aspartate and alanine. Ornithine, serine and glycine were detected in lower concentrations, but y-ammobutyric acid and citrulline were not detectable. This pattern was the same in both experiments and was unaffected by the type of N applied to the hyphae or by preincubation with albizzine, although the amino-acid concentration decreased considerably in expt 2 compared with expt 1. Both NH^*-N and NO3~-N were assimilated into amino acids but the levels of '°N enrichment following application of NO3~ were much lower than those following application of NH^^ indicating that the latter was more readily assimilated. Albizzine decreased the hyphal amino acid concentration by c. 30 % (without affecting the ^°N enrichment of the individual amino acids) indicating that the AM-fungal hyphae might possess a GS-GOGAT enzyme system for assimilation of inorganic N. The fattyacid profiles (especially phospholipid fatty acids 16:lw5 and 20:5) obtained from the hyphae of G. intraradices showed that contamination of the samples by fungi other than G. intraradices and bacteria was insignificant, and confirmed the usefulness of specific fatty-acid measurement to estimate soil AM-fungal content.

Transport of 15N from a soil compartment separated by a polytetrafluoroethylene membrane to plant roots via the hyphae of arbuscular mycorrhizal fungi

“…Using a PTFE membrane between the root compartment and hyphal compartment as a barrier to mobile ions, almost identical results were obtained in a simultaneously conducted experiment with maize (Zea mays) colonized by Glomus intraradices (Frey et al, 1998). Similar findings have been reported previously by Ames et al (1983), Johansen et al (1992Johansen et al ( , 1993Johansen et al ( , 1994Johansen et al ( , 1996, Frey & Schu$ epp (1993) and Tobar et al (1994). At a high N fertilizer concentration, the AMF-mediated transport of "&N from the hyphal compartment was reduced, as also observed by Johansen et al (1994).…”

“…However, in these systems the extent to which extraradical AMF hyphae can contribute to nutrient acquisition of plants remains difficult to determine because of unknown transport by diffusion and mass flow in the soil solution of mobile ions such as nitrate (Johansen et al, 1992(Johansen et al, , 1996Frey & Schu$ epp, 1993). To reduce diffusion and mass flow between the soil compartments, Faber et al (1991) used air gaps, paraffin wax or corn oil barriers, whilst Bethlenfalvay et al (1991) worked with a root-free soil bridge.…”

Synergistic effect of phosphate solubilizing rhizobacteria and arbuscular mycorrhiza on growth and yield of wheat plants

“…The enhanced uptake could also be due to an increase in the number of uptake sites per unit area of roots and a greater ability of these roots to exploit the soil for nutrients. AM hyphae are also known to transport inorganic N to the roots (Johansen et al, 1996).…”

Effect of the arbuscular mycorrhizal fungus Glomus fasciculatum on the uptake of amino nitrogen by Lolium perenne

“…Jakobsen & Jensen, perenne L.) in the presence of insect root herbivores. 1993; Bago et al, 1996;Johansen, Finlay & Olsson. Further work investigated the effect of the insect on 1996). A capacity for the external hyphae to take up the carbon and N economies of the clover plant and and deliver inorganic N has been demonstrated for identified the major N containing constituents of both ammonia (Ames et al, 1983) and nitrate (Bago root exudates.…”