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Abstract

The arbuscular mycorrhizal symbiosis is mutualistic, based on reciprocal transfer of P from the fungus to the plant and carbon from the plant to the fungus. Thus P is a most important 'currency' in the symbiosis. After absorbing P from the soil solution, the fungi first incorporate it into the cytosolic pool, and the excess P is transferred to the vacuoles. The vacuolar P pool probably plays a central role in P supply to the plant. The main forms of inorganic P in fungal vacuoles are orthophosphate and polyphosphate, but organic P molecules may also be present. Long distance translocation of P from the site of uptake in the external mycelium to the site of transfer to the plant is probably achieved via transfer of vacuolar components. This transport would be mediated either by protoplasmic streaming or the motile tubular vacuole-like system. The site of release of P into the interfacial apoplast and thence to the plant is most probably the fungal arbuscules. The biochemical and biophysical processes involved in P metabolism and transfer between cellular compartments in the symbiosis are currently not well understood. Some recent investigations of substrate specificities of phosphatase-type enzymes in AM fungi and other eukaryotic microorganisms, however, have shed new light on earlier results and permit the construction of a 1 hypothetical scheme of P-flow, including possible regulatory factors. Steps in this scheme are experimentally testable and should stimulate future research.

Arbuscular Mycorrhiza Augments Arsenic Tolerance in Wheat (Triticum aestivum L.) by Strengthening Antioxidant Defense System and Thiol Metabolism

“…This pathway overcomes severe diffusion limitation, bypasses the sharp depletion zones close to roots and delivers Pi direct to root cortical cells (Smith and Read, 2008). In addition, fungal translocation of P is extremely rapid, and involves movement of polyphosphate from sites of Pi absorption to sites of breakdown and transfer to plant cells (Ezawa et al, 2002). Since polyarsenate is not formed (due to low stability), As(V) cannot be translocated in the same way.…”

Effectiveness of native arbuscular mycorrhiza on the growth of four tree forest species from the Santa Marta Mountain, Veracruz (Mexico)

“…There is little specific information about the effects of AMF in Cojoba arborea (L.) Britton & Rose. However, most members of the Fabaceae family are nitrogen-fixing trees that establish AMF symbiosis which favor both P-uptake and rhizobial nodulation in roots (GuzmanPlazola & Ferrera-Cerrato, 1990;Ezawa et al, 2002). Wang & Qiu (2006) mentioned that 296 out of 315 species for the Fabaceae family, showed mycorrhizal symbiosis, 255 of them had arbuscular mycorrhiza (mainly associated with Glomus), and 41 had other types of mycorrhizal association.…”

Isolation and Characterization of Phosphate-Solubilizing Bacteria from Rhizosphere Soil

“…This reaction, manifested as a halo or a clear zone on the plate, is used for assessing the P-solubilizing activity of these bacteria. However, the reliability of this technique is questionable when it is the only one used in the detection of potential PSB (11,30).…”