Mycorrhizae plants

Maier, W., H. Peipp et al. (1995). Levels of a terpenoid glycoside (Blumenin) and cell wall-bound phenolics in some cereal mycorrhizas. Plant Physiol. 109(2) 465-470. 

Pfeffer, P. E., Douds, D. D., Becard, G. Shachar-Hill, Y. (1999). Carbon uptake and the metabolism and transport of lipids in an arbuscular mycorrhiza. Plant Physiology,... 

Weiss M, Mikolajewski S, Peipp H, Schmitt U, Schmidt J, Wray V, Strack D (1997) Tissue-specific and development-dependent accumulation of phenylpropanoids in larch mycorrhizas. Plant Physiol 114 15-27... 

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). 

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). 

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). 

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). 

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... 

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). 

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

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

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

M. C. Lemoine, V. Gianinazzi-Pearson, S. Gianinazzi, and C. J. Straker, Occurrence and expression of acid phosphatase of Hymeno.scypbus ericae (Read) Korf and Kernan, in isolation or as.sociated with plant roots. Mycorrhiza l 31 (1992). 

J. M. Barea, Mycorrhiza-bacteria interactions on plant growth promotion. Plant Growth Promoting Rhizohacteria (A. Ogoshi, K. Kobayashi, Y. Homma, F. Ko-dama, N. Kondo, and S. Akino, eds.), OECD Press, Paris, 1997, pp. 150-158. 

In addition, C. rangiferlna decreased N concentration of the jack pine. However, K+, Ca +, and Mg + concentrations in both receivers were not altered by either donor. Although mycorrhizae were associated with receiver plants in all the treatments, the authors concluded that impairment of either mycorrhizal function in absorbing P0 or P0 translocation in the receiver was responsible for decreased P0 uptake. They suggested that allelopathy might be responsible. 

In nature, most plant roots are invaded by fungi and transformed into mycorrhizae or "fungus roots" (25). The host plant and fungus form a symbiotic relationship whereby nutrients absorbed from the soil by the fungus are released into the host cell and the mycorrhizal fungus obtains nutrients from the host. Mycorrhiza formation is complex and depends on the dynamic interaction of the host plant, fungus and soil. Once formed, mycorrhizae have a profound influence on growth and development of the host plant (26-28). 

There are three distinct types of mycorrhizae, but the vesicular-arbuscular mycorrhiza is found on more plant species than... 

As stated earlier, mycorrhizae enhance nutrient absorption. Greater soil exploitation by mycorrhizal roots as a means of increasing phosphate uptake is well established. The normal phosphate depletion zone around non-mycorrhizal roots is 1-2 mm, but an endomycorrhizal root symbiont increased this zone to 7 cm (140). This ability to increase the nutritional level (particularly with regard to phosphorus), and subsequently the overall better growth dynamics of the mycorrhizal plant has been suggested as the reason for the salt (43) and drought (44-46) tolerance and increased nodulation (47) observed in mycorrhizal associations. Another interesting aspect of this enhanced nutrient uptake is the possible effect of mycorrhizae on competitive ability between two plant species. Under some conditions, mycorrhizal... 

If mycorrhizae are sites of action for allelochemicals, this is an important indirect aspect of allelopathic interaction among plants. Inhibition of mycorrhizal formation or a reduction in the efficiency of mycorrhizal association would reduce the nutrient level of the mycorrhizal plant and subsequently its competitiveness, stress tolerance or nodulation. Although allelochemicals have been implicated in the reduction of nodulation and nodule size, possible mycorrhizal involvement has not been examined. This is a difficult area of research but one that will provide better understanding of this complex situation. 

McGill and Cole (1981) suggested that the concentration of available P in the soil depended on biochemical mineralization, i.e., mineralization by extracellular enzymes, which does not provide energy to organisms and depends on the amount of enzymes present. This is controlled by the need for P. Thus, organic P input into the soil only influences the size of the total pool, while plants, microbes, and mycorrhiza can make P available by releasing phosphatases and phosphohydrolases into the soil. Phosphatase excretion has been used as an indicator of the P status of plants (Johnson et al. 1999 Phoenix et al. 2004). 

Fig. 6.3 Conceptual drawing of the distribution of different groups of herbaceous plants in relation to major plant nutrients. Cycles represent the distribution of grasses, herbs, and legumes. Species with mycorrhiza are able to exploit sites low in both nitrogen (N) and phosphorus (P). Highly productive species, such as ruderal plants, need conditions abundant in N and P. 

Decreased soil phosphatase activity and total P in aboveground plant biomass Increased microbial P mineralization (approx. 0.8 mg P kg-1 day1) and immobilization (approx. 6 mg P kg-1 day1) with higher moisture content No effect on soil phosphatase activities, plant P concentrations, or N/P ratios No effect on colonization of roots with mycorrhizae... 

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