Kinetics of NO3(-) net fluxes in Pinus pinaster, Rhizopogon roseolus and their ectomycorrhizal association, as affected by the presence of NO3(-) and NH4+.
The impact of mineral N supply, N-free or NO3(-) with or without NH4+, on the subsequent uptake of NO3(-) by maritime pine seedlings associated with the ectomycorrhizal fungus Rhizopogon roseolus was studied using ion-selective microelectrodes. NO3(-) net fluxes into N-starved non-mycorrhizal short roots (NMSRs) were low and measurable only over the NO3(-) concentration range of 0-70 microM. The simple kinetics observed in those roots may reflect the dominant operation of a high-affinity NO3(-) transport system (HATS) which is constitutive. NO3(-) pretreatment increased the NO3(-) net fluxes and led to a complex kinetics that may reflect the operation of other HATS. A simple kinetics was observed in plants pre-incubated at high NH4+ concentration. In contrast, NO3(-) uptake kinetics presented only one saturation phase in the fungus, whether associated with the plant or not. NO3(-) uptake was greater after a pretreatment in N-free or NO3 (-) solution, but NH4+ pretreatment led to a threefold reduction in NO3 (-) uptake. These results suggest that the regulation of NO3(-) transport systems varies between the host and the fungal partner. This variation is likely to contribute to the positive effect of mycorrhizal association on N uptake in plants when the N supply is low and fluctuating.
Gobert
Anthony
A
UMR 1222 INRA/SupAgro, Rhizosphère & Symbiose, 2, Place Viala, 34060 Montpellier Cedex 01, France.
Plassard
Claude
C
D001487:Basidiomycota / Q000187:drug effects / Q000502:physiology*; D003470:Culture Media; D004875:Ergosterol / Q000378:metabolism; D007700:Kinetics; D025282:Mycelium / Q000187:drug effects; D038821:Mycorrhizae / Q000187:drug effects / Q000502:physiology*; D009566:Nitrates / Q000378:metabolism* / Q000494:pharmacology; D009584:Nitrogen / Q000378:metabolism; D028223:Pinus / Q000187:drug effects / Q000378:metabolism* / Q000382:microbiology*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism* / Q000494:pharmacology; D036226:Seedlings / Q000187:drug effects
D003470:Culture Media; D009566:Nitrates; D000644:Quaternary Ammonium Compounds; D009584:Nitrogen; D004875:Ergosterol