Ectomycorrhizal

The transformation of 4-fluorobiphenyl by the ectomycorrhizal fungus Tylosporafibrilosa was studied by NMR (Green et al. 1999) and the principal products were 4-fluorobi-phen-3 -ol and 4-fluorobiphen-4 -ol. 

Arbutoid mycorrhizae Members of the Ericales with sturdier roots including Arbutus, Arctostaphylos. and Pyrola-ceae Ectomycorrhizal fungi on other types of plants Fungal mantle, Hartig net and coils... 

These DNA markers have been successfully employed to track specific strain-associated loci in endo- and ectomycorrhizal populations from agricultural land, forest nurseries, plantations, and natural ecosystems. The simplest strategy (digesting PCR-amplified ITS with selected endonucleases) has identified their symbionts in various ecosystems (18,36-38). Species discrimination by ITS-RFLP matching can be improved by comparing data for the targeted DNA with those on sequence databases (37). 

Root flavonoids that may act as signals for the initiation and development of endomycorrhizal and ectomycorrhizal symbio.ses have been identified (see Chap. 7). Metabolites of the phenylpropanoid pathways apparently act as signaling molecules in endo- and ectomycorrhizal interactions (14). The role of flavonoids is still controversial, but a variety of flavanones, flavones, and isoflavones... 

The effect of flavonoids on spore germination and hyphal growth of ecto-mycorrhizal fungi is poorly known. However, several metabolites relea.sed by the plant roots trigger events leading to their infection (44,55). In the saprotrophic phase, spores of several ectomycorrhizal fungi respond to stimulation by abietic acid, the diterpene resin acid, in root exudates (56). 

In cricoid or ectomycorrhizal fungi, the thickness of the hyphal cell wall is much the same in presymbiotic and symbiotic hyphae, although the fibrillar material on the surface of ericoid fungi outside the root disappears during penetration (69). 

Changes in cell-wall protein composition may regulate the molecular architecture of protein networks in a manner that allows new developmental outcomes for both fungal cell adhesion and root colonization. Further investigation of the structure and regulation of SRAP wall proteins will provide a more complete picture of their role in developing ectomycorrhizal tissues. Incompatibility between ectomycorrhizal hyphae and the host roots detected during the initial con-... 

The morphological and physiological dissimilarities between mycorrhizal symbi-o.ses probably determine their success and their distinct patterns in different ecosystems (92). Nitrogen (N) available to both AM and ectomycorrhizal plants should not be regarded as a single pool open to free competition. Specialization of its acquisition and utilization in a given habitat is an important feature of plant and microbial community structure, while the fact that the ability to exploit its sources (and tho.se of other limited nutrients) is not the same in all species may result in niche differentiation (93). If habitat specialization is a reflection of differences between mycorrhizal types, ectomycorrhizal and AM species could cooccur because they exploit different niches in the. same ecosystem. 

In the forest ecosystems of Eurasia and North America, where ectomycorrhizal a.ssociations are dominant, there are often wide variations in the environmental concentration of N and its forms, and its limited availability to plants is... 

Figure 11 The different steps of nitrogen metabolism in the extraradical hyphae, ccto-mycorrhizal roots, and roots of the host plant. I, absorption 2, assimilation 3. storage 4. translocation A, extramatrical hyphae B. ectomycorrhizal sheath C, Hartig net D, root cortical cells AA amino. acids.

The growth of ectomycorrhizal trees is frequently improved by their increased phosphorus (P) accumulation (3), and this, in turn, is related to the intensity of the mycorrhizal infection. Ectomycorrhizal fungi solubilize insoluble forms of A1 and Ca phosphates as well as inositol hexaphosphates, though a wide interstrain variability has been recorded (112). These complex P forms are digested by the secretion of extracellular acid and alkaline phosphomono- and phosphodi-ester-ases. Pi in soil solutions is easily taken up by ectomycorrhizal hyphae and then translocated to the host roots. Its absorption and efflux are probably regulated... 

Recent reviews have focused on the role of mycorrhizal fungi in the uptake of heavy metals from polluted soils and their transfer to the plant (123). Several experimental data provide clear evidence that both ectomycorrhizal and ericoid fungi protect their host against these metals (123-125). The position with regard to the AM fungi is less clear (123). 

F. Martin, M. A. Selos.se, C. Di Battista. H. Gherbi, C. Delaruclle, D. Vairelles, D. Bouchard, and F. Le Tacon, Molecular markers in ecology of ectomycorrhizal fungi. Genet. Select. Evol. 30 5333-5355 (1998). 

M. A Selosse, G. Costa, C. Dibattista, F. Letacon, and F. Martin, Meiotic segregation and recombination of the intergenic spacer of the ribosomal DNA in the ectomycorrhizal basidiomycete Laccaria hicolor. Curr. Gen. 30 332 (1996). 

H. Gryta, J. C. Debaud, A. Effosse, G. Gay, and R. Marmeisse, Fine-scale structure of populations of the ectomycorrhizal fungus HeheUnna cylindrosponim in coastal sand dune forest ecosystems. Mol. Ecol. 6 353 (1997). 

M. Gardes and T. D. Bruns, Community structure of ectomycorrhizal fungi in a Pinu.s niuricata forest above and below-ground views. Can. J. Hot. 74 1572 (1996). 

O. Karen, N. Hogberg, A. Dahlberg, L. Jonsson, and J. E. Nylund, Inter- and intraspecific variation in the ITS region of rDNA of ectomycorrhizal fungi in Fennoscan-dia as detected by endonuclea.se analysis. New Phytol. /36 3I3 (1997). 

T. Beguiristain, R. Cote, P. Rubini, C. Jayallemand, and F. Lapeyrie, Hypaphorine accumulation in hyphae of the ectomycorrhizal fungus Pisolithus tinctorius. Phytochemistry 40 1089 (1995). 

T. Beguiristain and F. Lapeyrie, Host plant stimulates hypaphorine accumulation in Pisolithus tinctorius hyphae during ectomycorrhizal infection while excreted fungal hypaphorine controls root hair development. New Phytol. 136 525 (1997). 

D. Tagu. B. Nasse, and F. Martin, Cloning and characterization of hydrophobins-encoding cDNAs from the ectomycorrhizal basidiomycete Pi.solithiis tinctorius. Gene 168 93 (1996). 

Finlay, R. D., Ek, FI., Odham, G., and Soderstrom, B. Mycelium uptake, translocation and assimilation of nitrogen from N-labelled ammonium by Pintis. sylvestris plants infected with four different ectomycorrhizal fungi. New Phytol. //0 59-66 (1988). 

F. Paris, P. Bonnaud, J. Ranger, M. Robert, and F. Lapeyrie, Weathering of ammonium- or calcium-saturated 2 1 phyllosilicates by ectomycorrhizal fungi in vitro. Soil Biol. Biochein. 27 1237 (1995). 

F. Martin and B. Botton, Nitrogen metabolism of ectomycorrhizal fungi and ecto-mycorrhiza. Adv. Plant Pathol. 9 83 (1993). 

G. D. Bending and D. J. Read, Effect of the soluble polyphenol tannic acid on the activities of ericoid and ectomycorrhizal fungi. Soil Biol. Biochem. 2ft 1595 (1996). 

H. Vare, Aluminum polyphosphate in the ectomycorrhizal fungus Siiillus variega-tiis (Fr.) O. Kuntze as revealed by energy dispersive spectrometry. New Phytol. 7/6 663 (1990). 

Bending, G.D. Read, D.J. 1995. The Structure and Function of the Vegetative Mycelium of Ectomycorrhizal Plants. 5. Foraging Behavior and Translocation of Nutrients from Exploited Litter. New Phytologist, 130.3, 401-09. 

Frey B, Brunner I, Walther P, Scheidegger C, Zierold K. Element localization in ultrathin cryosections of high-pressure frozen ectomycorrhizal spruce roots. Plant Cell Environ 1997 20 929-937. 

---