Extraradical hyphae

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.

Hardie, K. (1985). The effect of removal of extraradical hyphae on water uptake by vesicular-arbuscular mycorrhizal plants. New Phytologist, 101, 677-84. 

Koide, R. T. Kabir, Z. (2000). Extraradical hyphae of the mycorrhizal fungus Glomus intraradices can hydrolyse organic phosphate. New Phytologist, 148, 511-17. 

AM fungi contribute to plant growth and plant nutrition as their extraradical hyphae increase the volume of the explored soil. These extraradical hyphae can extend up to more than 10 cm from the roots (Harley and Smith, 1983) and make up a hyphal density of 1-30 m g soil (Smith and Read, 1997). Therefore, AM roots can more easily access soil nutrients localized outside the root depletion zone, especially the nonmobile elements such as P and Zn. Mycorrhizas also improve plant water uptake, stress tolerance, and affect the microbial community structure (loner et al, 2001). In polluted soils, mycorrhizal plants also benefit from the presence of the AM fungi. 

Internal sequestration by extraradical hyphae (Berreck and Haselwandter,... 

Although information on U speciation in the mycorrhizosphere is lacking in the literature, it is obvious that the development of extraradical hyphae can influence U speciation through hyphal-induced pH changes. 

Numerous studies have shown that the effectiveness of the extraradical hyphae in taking up elements varied greatly between fungal species. The distinct... 

Indeed, the inflow rates of P in extraradical hyphae may range from 2 to 20 x 10 mol m s [96-99], while bidirectional protoplasmic flow rate, measured on the basis of cellular particles movement (presumably vacuoles, nuclei, fat droplets, organelles, granules), ranges from 2.98 to 4.27 pm s [100, 101]. However, it is important to underline that the most important factor affecting the transfer of nutrients from soil to root-based hyphae is represented by the flux of mineral nutrients through appressoria, which for P is 3.8 x 10 mol cm s [102]. 

Fundamental information on the transport of nraninm by mycelinm of arbuscular mycorrhizal (AM) fungi is reported and discnssed in this chapter. The monoxenic cultivation system was shown to be convenient to investigate the processes of nptake and translocation of U by AM fungi, as it was already reported for some other elements. The evidence that extraradical AM hyphae can take np U and translocate it towards the host roots was clearly shown. Further research to understand the mechanisms involved and future prospects were also suggested. 

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