Association of highly and weakly mycorrhizal seedlings can promote the extra- and intraradical development of a common mycorrhizal network.

Arbuscular mycorrhizal fungi (AMF) are key determinants of plant interactions in ecosystems. Through their effects on competition, they are regulators of the structure of communities. Conversely, the composition of plant assemblages may also influence the AMF colonization dynamics of plant species.

Elemental composition in vesicles of an arbuscular mycorrhizal fungus, as revealed by PIXE analysis.

We investigated element accumulation in vesicles of the arbuscular mycorrhizal (AM) fungus Glomus intraradices, extracted from the roots of inoculated leek plants. The elemental composition (elements heavier than Mg) was quantified using particle-induced X-ray emission (PIXE), in combination with scanning transmission ion microscopy (STIM). In vesicles, P was the most abundant of the elements analysed, followed by Ca, S, Si and K.

Fenpropimorph and fenhexamid impact phosphorus translocation by arbuscular mycorrhizal fungi.

Fenpropimorph and fenhexamid are sterol biosynthesis inhibitor (SBI) molecules widely used to control diseases in agriculture. Both molecules, at increasing concentrations, have been shown to impact on the non-target arbuscular mycorrhizal (AM) fungi. Root colonization, spore production and mycelium architecture, including the branched absorbing structures which are thought to be involved in phosphorus (P) uptake, were affected.

Two differentially regulated phosphate transporters from the symbiotic fungus Hebeloma cylindrosporum and phosphorus acquisition by ectomycorrhizal Pinus pinaster.

Ectomycorrhizal symbiosis markedly improves plant phosphate uptake, but the molecular mechanisms underlying this benefit are still poorly understood. We identified two ESTs in a cDNA library prepared from the ectomycorrhizal basidiomycete Hebeloma cylindrosporum with significant similarities to phosphate transporters from the endomycorrhizal fungus Glomus versiforme and from non-mycorrhizal fungi. The full-length cDNAs corresponding to these two ESTs complemented a yeast phosphate transport mutant (Deltapho84).

Genomics of pyrrolnitrin biosynthetic loci: evidence for conservation and whole-operon mobility within gram-negative bacteria.

Pyrrolnitrin (PRN) is a tryptophan-derived secondary metabolite produced by a narrow range of gram-negative bacteria. The PRN biosynthesis by rhizobacteria presumably has a key role in their life strategies and in the biocontrol of plant diseases. The biosynthetic operon that encodes the pathway that converts tryptophan to PRN is composed of four genes, prnA through D, whose diversity, genomic context and spread over bacterial genomes are poorly understood.

Fluorescent in situ RT-PCR to visualise the expression of a phosphate transporter gene from an ectomycorrhizal fungus.

Expression of a mycorrhizal fungal-specific phosphate (P) transporter gene (HcPT1) was studied in mycelium of the ectomycorrhizal fungus Hebeloma cylindrosporum, by in situ reverse transcriptase polymerase chain reaction using amplification of complementary DNA sequences. The expression of HcPT1 was visualised under two different P treatments. Mycelium was transferred to liquid medium with or without P and incubated for 5 days.

The influence of external nitrogen on carbon allocation to Glomus intraradices in monoxenic arbuscular mycorrhiza.

The influence of external nitrogen (N) on carbon (C) allocation and processes related to phosphorus (P) metabolism were studied in monoxenic arbuscular mycorrhiza (AM) cultures of Daucus carota. Fungal hyphae of Glomus intraradices proliferated from colonized roots growing on solid medium into C-free liquid minimal medium with two different N and P levels. Furthermore, we exposed the colonized roots to high or low N availability and then studied the mycelial development.

13C incorporation into signature fatty acids as an assay for carbon allocation in arbuscular mycorrhiza.

The ubiquitous arbuscular mycorrhizal fungi consume significant amounts of plant assimilated C, but this C flow has been difficult to quantify. The neutral lipid fatty acid 16:1omega5 is a quantitative signature for most arbuscular mycorrhizal fungi in roots and soil. We measured carbon transfer from four plant species to the arbuscular mycorrhizal fungus Glomus intraradices by estimating (13)C enrichment of 16:1omega5 and compared it with (13)C enrichment of total root and mycelial C.

Metabolic activity of Glomus intraradices in Arum- and Paris-type arbuscular mycorrhizal colonization.

Colonization of two plant species by Glomus intraradices was studied to investigate the two morphological types (Arum and Paris), their symbiotic interfaces and metabolic activities. Root pieces and sections were stained to observe the colonization and metabolic activity of all mycorrhizal structures. There were no growth responses observed in the plants caused by mycorrhizal symbiosis.

Fungal lipid accumulation and development of mycelial structures by two arbuscular mycorrhizal fungi.

We monitored the development of intraradical and extraradical mycelia of the arbuscular mycorrhizal (AM) fungi Scutellospora calospora and Glomus intraradices when colonizing Plantago lanceolata. The occurrence of arbuscules (branched hyphal structures) and vesicles (lipid storage organs) was compared with the amounts of signature fatty acids. The fatty acid 16:1omega5 was used as a signature for both AM fungal phospholipids (membrane constituents) and neutral lipids (energy storage) in roots (intraradical mycelium) and in soil (extraradical mycelium).

Phosphorus effects on metabolic processes in monoxenic arbuscular mycorrhiza cultures.

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.

Arbuscular mycorrhizal fungi respond to the substrate pH of their extraradical mycelium by altered growth and root colonization.

•  To test the response of arbuscular mycorrhizal (AM) fungi to a difference in soil pH, the extraradical mycelium of Scutellospora calospora or Glomus intraradices, in association with Plantago lanceolata, was exposed to two different pH treatments, while the root substrate pH was left unchanged. •  Seedlings of P. lanceolata, colonized by one or other of the fungal symbionts, and nonmycorrhizal controls, were grown in mesh bags placed in pots containing pH-buffered sand (pH around 5 or 6).