Polyphosphate has a central role in the rapid and massive accumulation of phosphorus in extraradical mycelium of an arbuscular mycorrhizal fungus

Abstract

The dynamics of polyphosphate with respect to toal phosphorus and orthophosphate levels in an arbuscular mycorrhizal association were investigated to clarify the role of polyphosphate in the symbiotic phospharus-translocation.Lotus japonicus was inoculated with Glomus sp. HR1 and grown in a two- compartment culture system in which hyphal and mycorrhizal compartments were separated by nylon mesh bags. Extraradical hyphae and mycorrhizal roots were collected from the hyphal and mycorrhizal compartments, respectively, at one h interval after phosphate application to the hyphal compartment, and polyphosphate, total phosphorus and orthophosphate levels were determined. Total phosphorus and polyphosphate levels in hyphae in the hyphal compartment increased and decreased synchronously after phosphate application, while orthophosphate levels remained constant at lower levels. The level of polyphosphate reached 64% of total phosphorus 5 h after phosphate application. Decreases in polyphosphate in hyphae in the hyphal compartment were concurrent with increases in polyphosphate in the mycorrhizal roots + hyphae in the mycorrhizal compartment. The present study demonstrated that the potential capacity of arbuscular mycorrhizal fungal cell for polyphosphate accumulation was much larger than those reported previously and suggested that polyphosphate plays a central role in the mediation of long-distance phosphorus-translocation through hyphae

Suppression of Arbuscule Degeneration in Medicago truncatula phosphate transporter4 Mutants Is Dependent on the Ammonium Transporter 2 Family Protein AMT2;3

“…The current models suggest that Pi and N move as polyphosphate (polyP) and arginine, respectively, and that translocation through the hyphae occurs in vacuoles (Cox et al, 1980;Govindarajulu et al, 2005;Cruz et al, 2007;Hijikata et al, 2010). In yeast, polyP and arginine are physically associated and a similar suggestion has been made for AM fungi (Durr et al, 1979;Govindarajulu et al, 2005).…”

The expression of GintPT, the phosphate transporter of Rhizophagus irregularis, depends on the symbiotic status and phosphate availability

“…After hydrolysis, Pi is exported from the AM fungus to the periarbuscular space, where it is taken up by plant cortical cells (Javot et al 2007). Poly-Pi is the largest P storage and a mediator of long distance P translocation in AM fungi (Hijikata et al 2010). It remains uncertain whether P is translocated as poly-Pi without turning over, or whether it is translocated as Pi through a dynamic regulation of poly-Pi synthesis/hydrolysis (Ezawa et al 2001).…”

The Role of the Mycorrhizal Symbiosis in Nutrient Uptake of Plants and the Regulatory Mechanisms Underlying These Transport Processes

“…The average length of short chained polyP in AM fungi has been estimated as 11-20 Pi [78,79], and of long chained polyP as 190 to 300 Pi residues [80,81]. Mycorrhizal fungi can rapidly store a significant proportion (more than 60%) of their cellular P as polyP [69,82,83]. In the mycorrhizal symbiosis, polyP are involved in:…”

“…The exploration of large soil volumes by the ERM in which orthophosphate (Pi) is scavenged and delivered to plant cortical cells, bypassing the plant pathway for P uptake [66,67] (Figure 4);  The small hyphal diameter that allows the fungus to penetrate into small soil cores in search for P, and higher P influx rates per surface unit [66,68];  The capability of mycorrhizal fungi to store P in form of polyphosphates, which allows the fungus to keep the internal Pi concentration relatively low, and allows an efficient transfer of P from the ERM to the IRM [69]; and  The production and secretion of acid phosphatases and organic acids that facilitate the release of P from organic complexes [70,71].…”