Effect of P availability on temporal dynamics of carbon allocation and glomus intraradices high-affinity P transporter gene induction in arbuscular mycorrhiza.
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.
Olsson
Pål Axel
PA
Department of Ecology, Ecology Building, Lund University, SE 223 62 Lund, Sweden. Pal_Axel.Olsson@ekol.lu.se
Hansson
Maria C
MC
Burleigh
Stephen H
SH
D018533:Biomass; D002244:Carbon / Q000378:metabolism; D007700:Kinetics; D008055:Lipids / Q000032:analysis; D038821:Mycorrhizae / Q000302:isolation & purification / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism; D010944:Plants / Q000382:microbiology*
D008055:Lipids; D010743:Phospholipids; D002244:Carbon