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Appl Environ Microbiol. 2006 Jun;72(6):4115-20.

Effect of P availability on temporal dynamics of carbon allocation and glomus intraradices high-affinity P transporter gene induction in arbuscular mycorrhiza.

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1
Department of Ecology, Ecology Building, Lund University, SE 223 62 Lund, Sweden. Pal_Axel.Olsson@ekol.lu.se

Abstract

Arbuscular mycorrhizal (AM) fungi depend on a C supply from the plant host and simultaneously provide phosphorus to the colonized plant. We therefore evaluated the influence of external P on C allocation in monoxenic Daucus carota-Glomus intraradices cultures in an AM symbiosis. Fungal hyphae proliferated from a solid minimal medium containing colonized roots into a C-free liquid minimal medium with high or low P availability. Roots and hyphae were harvested periodically, and the flow of C from roots to fungus was measured by isotope labeling. We also measured induction of a G. intraradices high-affinity P transporter to estimate fungal P demand. The prevailing hypothesis is that high P availability reduces mycorrhizal fungal growth, but we found that C flow to the fungus was initially highest at the high P level. Only at later harvests, after 100 days of in vitro culture, were C flow and fungal growth limited at high P availability. Thus, AM fungi can benefit initially from P-enriched environments in terms of plant C allocation. As expected, the P transporter induction was significantly greater at low P availability and greatest in very young mycelia. We found no direct link between C flow to the fungus and the P transporter transcription level, which indicates that a good C supply is not essential for induction of the high-affinity P transporter. We describe a mechanism by which P regulates symbiotic C allocation, and we discuss how this mechanism may have evolved in a competitive environment.

PMID:
16751522
PMCID:
PMC1489668
DOI:
10.1128/AEM.02154-05
[Indexed for MEDLINE]
Free PMC Article
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