Mycorrhizae

Accumulation in soil solutions Altered microflora Reduced litter decomposion Metal ions accumulate Reduced water/mineral uptake Reduction in mycorrhizae Reduced vigor/resistance... 

Hans, J. et al.. Cloning, characterization, and immunolocalization of a mycorrhiza-inducible 1-deoxy-d-xylulose 5-phosphate reductoisomerase in arbuscule-containing cells of maize, Plant Physiol. 134, 614, 2004. 

Chapters 7 and 9 discuss specific exchange of molecular signals (the so-called molecular cross talk ) between beneficial microorganisms, such as rhizo-bia and mycorrhizas, and their host plants. Molecular cross talk seems to be a prerequisite mechanism for most of the plant infection by soil microorganisms (14). Only for a few microbial infections, however, the sequence and type of molecular signals involved have been characterized. Thus, there is the need for further studies to elucidate the unknown molecular cross talk between the most common rhizobacteria and fungi and the plant roots it is also needed to better understand how molecular cross talk responds to the changing environmental conditions. The potential applications of these studies are important because the... 

This chapter considers the various types of root products with a potential functional role in the usually tough environment of soil. Only direct effects of immediate benefit to plant growth—e.g., an increase in nutrient solubility—are considered here. Although root products of a plant species may have a direct effect on important groups of soil organisms, such as rhizobia and mycorrhizae. their effect on the plant is not immediate these and aspects related to microbial activity in the rhizosphere are not considered here (see Chaps. 4, 7, and 10). For an extensive and recent review of the microorganisms in the rhizosphere, the reader is referred to Bowen and Rovira (23). 

Root products, as defined by Uren and Reisenauer (17), represent a wide range of compounds. Only secretions are deemed to have a direct and immediate functional role in the rhizosphere. Carbon dioxide, although labeled an excretion, may play a role in rhizosphere processes such as hyphal elongation of vesicular-arbuscular mycorrhiza (39). Also, root-derived CO2 may have an effect on nonphotosynthetic fixation of CO2 by roots subject to P deficiency and thus contribute to exudation of large amounts of citrate and malate, as observed in white lupins (40). The amounts utilized are very small and, in any case, are extremely difficult to distinguish from endogenous CO2 derived from soil and rhizosphere respiration. 

R. Kape, K. Wex, M. Pamiske, E. Gorge, A. Wetzel, and D. Werner, Legume root metabolites and VA-mycorrhiza development. J. Plant Physiol. 141 54 (1992). 

S. M. Schwab, J. A. Menge, and R. T. Leonard, Quantitative and qualitative effects of phosphorus on extracts and exudates of sudangrass roots in relation to vesicular-arbuscular mycorrhiza formation. Plant Physiol. 73 761 (1983). 

M. G. Nair, G. R. Safir, and J. O. Siqueira, Isolation and identification of vascular-arbuscular mycorrhiza-stimulatory compounds from clover (Trifolium repens) roots. AppL Environ. Microbiol. 57 434 (1991). 

The presence of microorganisms in the rhizosphere has been shown to increa.se root exudation (58,61-65). This stimulation of exudation has been shown to occur in the pre.sence of free-living bacteria such as Azospirillum spp. and Azotobacter spp. (66,67) and in the presence of symbiotic organisms such as mycorrhizae (68,69). Increased root exudation has also been shown to be species-specific for example Meharg and Killham (65) found that metabolites produced by Pseudomonas aeru/ inosa stimulated a 12-fold increase in C-labeled exudates by perennial ryegrass. However, under the same conditions, metabolites from an Arthro-bacter species had no effect on root exudation. 

R. C. Snellgrove, W. E. Splitstoesser, D. B. Strubket, and P. B. Tinker. The distribution of carbon and the demand of the fungal symbiont in leek plants with vesicular-arbuscular mycorrhizas. New Phytologist 69 15 (1982). 

A. Varma and B. Hock, Mycorrhiza, Springer-Verlag, Berlin, 1995. 

N. S. Bolan, A. D. Robson, and N. J. Barrow, Effects of vesicular-arbuscular mycorrhiza on the availability of iron phosphates to plants. Plant and Soil 99 40l (1987). 

R. G. Linderman, Vesicular-arbuscular mycorrhizae and soil microbial interactions, Mycorrhizae in Sustainable Agriculture (G. J. Bethlenfalvay and R. G. Linderman, eds.), American Society of Agronomy, Madison, Wisconsin, 1992, p. 45. 

D. Werner, S. Bernard, E. Gorge, A. Jacobi, R. Rape, K. Kosch, M. Pamiske, S. Schenk, P. Schmidt, and W. Streit, Competitiveness and communication for effective inoculation by Rhizohium, Bradyrhizohium and vesicular-arbuscular mycorrhiza fungi. Experientia. 50 884 (1994). 

Mycorrhizae Host plants Fungal symbionts Fungal structures... 

Arbuscular mycorrhizae Many plant species, including representatives of bryophytes, gymnosperms, and many angio-sperms Glomales Appressoria. inter- and intracellular hyphae, coils, arbuscules, vesicles... 

Orchyd mycorrhizae All members of the Orchidaceae Many isolates from sterile myce-lia referable to form genus Rhi-zoctonia. induced to form sexual stages, referable to about 8 genera of Basidiomycotina including some pathogens Coils... 

Ericoid mycorrhizae Members of the Ericales with fine hair roots, especially Eri-coideae, Vaccinoideae, Rhodo-dendroideae, Epacridaceae and Empetraceae Hymenoscyphus isolates, Oidio-dendrum griseum sterile i.solate Coils... 

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... 

Early interactions between the cell walls of the plant and the fungus and changes in their composition are essential morphogenetic events in the constitution of a functioning mycorrhiza. Cellular and molecular approaches have provided new insights into the complex and ever-changing scenario of these interactions. Cytochemical and in situ immunological techniques have demonstrated that both structure and function are less complex when assessed at the cell level (10,11,71,72). 

M. G. Allen, Functioning Mycorrhizae, Chapman Hall, New York, London, 1992. 

S. Gianinazzi and H. Schuepp, Impact of arbuscular mycorrhizas on sustainable agriculture and natural ecosystems, Birkhauser Verlag, Basel, 1994. 

J. C. Debaud, R. Marmeisse, and G. Gay, Intraspecilic genetic variation in ectoniy-corrhizal fungi, Mycorrhiza (A. K. Varma and B. Hock, eds.), Springer-Verlag, Berlin Heidelberg, 1995, pp. 29-58. 

R. Agerer, Characterization of ectomycorrhiza. Methods in Microbiology Tech-nitpies for the Study of Mycorrhiza (J. R. Norris, D. J. Read, and A. K. Varma. eds.). Academic Pres.s, London, 1991, pp. 25-74. 

M. Gardes, T. D. and Bruns, ITS primers with enhanced specificity for Basidiomy-cetes application to identification of mycorrhizae and rusts. Mol. Ecol. 2 113 (1993). 

F. Martin, G. Costa, C. Delaruelle, and J. Diez, Genomic fingerprinting of ectomy-corrhizal fungi by microsatellite-primed PCR, Mycorrhiza Mcimial (A Varma, B Hock, eds,). Springer lab manual, 1998, pp, 463-474. 

J. P. Clapp, J. P. W. Young, J. P. Merryweather, and A. H. Fitter. Diversity of fungal symbionts in arbu.scular mycorrhizas from a natural community. New Phytol. 130 259 (1995). 

D. A. Phillips and S. M. Tsai, Flavonoids as plant signals to rhizosphere microbes. Mycorrhiza 1 55 (1992). 

I. Kottke, Fungal adhesion pad formation and penetration of root cuticle in early stage mycorrhizas of Picea abies and Laccaria amethystea. Protoplasma 196 55 (1997). 

J. Dexheimer and J. C. Pargney, Comparative anatomy of the host-fungus interface in mycorrhizas. Experientia 47 312 (1991). 

R. L. Peterson and P. Bonfante, Comparative structure of vesicular-arbuscular mycorrhizas and ectomycorrhizas. Plant Soil 159 19 (1994). 

J. S. Pate, The mycorrhizal association just one of many nutrient acquiring specializations in natural ecosystems. Management of Mycorrhizas in Agriculture, Horticulture and Forestry (A. D. Robson, L. K. Abbott, and N. Malajezuk. eds.). Kluwer Academic Publishers, 1994, pp. 1-10. 

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