Nutrient transfer in arbuscular mycorrhizas: how are fungal and plant processes integrated?

By Sarah E. Smith, S. Dickson, F. Andrew Smith. 2001

138 citations recorded by the source corpus.

This review brings together recent work on the coordination of transport processes between fungus and plant symbionts in arbuscular mycorrhizal (AM) symbioses, and focuses on new information on the diversity in structure and function of interfaces and their potential roles in transport processes. We consider the way that fungal activity is polarised to absorb mineral nutrients (especially phosphorus, P) in soil, transport them to the root and release them to the plant. Conversely, the fungal structures within the root appear to be specialised to absorb sugars, which the external mycelium cannot do. The external mycelium depends on a supply of lipid, transported from within the root. High affinity P transporters expressed in the root apices and root hairs of non-mycorrhizal roots, and most probably mycorrhizal roots, absorb P actively. This can result in the development of P depletion zones, so that a low concentration of P at the absorbing surfaces limits further uptake. The external hyphae of AM fungi extend well beyond the depletion zone, accessing supplies of P at a distance and in narrow soil pores, that is absorbed actively by a high affinity P transporter expressed in these small diameter hyphae. Translocation of P within the hyphae and transfer to the plant results in much higher rates of uptake (inflows) by mycorrhizal than non-mycorrhizal roots. The possible role of polyphosphate (polyP) in this process is discussed in the light of new data. Within the root, P is lost from the fungal structures to the interfacial apoplast by an unknown mechanism, and is absorbed by the root cortical cells. The expression of a high affinity P transporter and H + -ATPase in arbuscule-containing cells indicates that these are probably the sites of fungus/plant P transfer. The site of sugar transfer from plant to fungus has not yet been established. At the whole plant level, plant uptake systems located in the youngest regions of the root are positioned to absorb P from undepleted soil, into which the root apex has just grown. In older regions of the roots, colonised by mycorrhizal fungi, the external mycelium will take over the absorptive role and overcome the difficulties posed by the slow diffusion of P in soil.

Subfields: Plant Science

View Paper: https://www.semanticscholar.org/paper/d0210d453f1eef863d08593e7886052201be2b9e

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Citations in the corpus

Exploring structural definitions of mycorrhizas, with emphasis on nutrient-exchange interfaces (2004, background): “Currently there is considerable interest in characterizing transporters in both the periarbuscular membrane and the fungal membrane, since these would be involved in the active transport across this interface (Harrison 1999a, 1999b; Smith et al. 2001; Ferrol et al. 2002).”
Facilitated legume nodulation, phosphate uptake and nitrogen transfer by arbuscular inoculation in an upland rice and mung bean intercropping system (2009, background): “Transport of P into host plants and its release to root cells is an important function of AMF (Ryan et al. 2007; Smith et al. 2001).”
Nitrogen Transfer Within and Between Plants Through Common Mycorrhizal Networks (CMNs) (2003, background): “Their hyphal tips actively take up inorganic nutrients from soil, particularly phosphorus (P), which is then translocated to the plant partner (Smith and Smith, 1990, 2001; Smith et al., 1994; Frey et al., 2000; Kapulnik and Douds, 2000).”
Phloem loading and unloading of sugars and amino acids (2003, unknown): “HXTs also perform a similar function in filial tissues of tropical cereals (Thomas, Felker & Crawford 1992) and fungal partners of mycorrhizas (Smith et al. 2001).”
Use of 15N stable isotope to quantify nitrogen transfer between mycorrhizal plants (2009, background): “2004, 2005), P (Smith et al. 2001), arsenic (P analog), cesium and rubidium (K analogs) (Meding and Zasoski 2008), water (Egerton-Warburton et al.”
Phosphorus acquisition and use: critical adaptations by plants for securing a nonrenewable resource. (2003, background): “Localization of plant uptake systems in the youngest regions of roots and in the root hairs is most effective for recovery of nutrients from undepleted soil (Smith et al., 2001).”
The Role of PHT1 Family Transporters in the Acquisition and Redistribution of Phosphorus in Plants (2019, background): “AMF enhance Pi availability to plants by acting as the functional extensions of the plant root system in exchange for plant carbohydrates in LP soils (Smith et al., 2001).”
Phosphorus Acquisition Strategies within Arbuscular Mycorrhizal Fungal Community of a Single Field Site (2005, unknown): “E-mail jan.jansa@ipw.agrl.ethz.ch roots (Cooper and Tinker, 1978; Sanders and Tinker, 1971; Smith et al., 2001).”
Darkness visible: reflections on underground ecology (2005, unknown): “Almost certainly, phosphate ions move from fungus to plant across this membrane interface, while the fungus receives fixed carbon from the plant, either at this same interface or in the apoplasts where the fungal hyphae grow between the cortical cells (Smith et al. 2001).”
Plant Growth-Promoting Effects of Diazotrophs in the Rhizosphere (2003, background): “AM can improve plant growth through increased uptake of P and other mineral nutrients especially in soils of low fertility (Ning and Cumming, 2001; Rao and Tak, 2001; Smith et al., 2001).”
Arsenic uptake and toxicity in plants: integrating mycorrhizal influences (2010, background): “The conventional view has been that the AM and direct pathways of Pi uptake act additively to provide P to plants, and that colonisation by the fungi does not affect the amount of Pi absorbed via the direct pathway (Smith et al. 2001).”