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Type: Journal article
Title: Kinetics of ammonium and nitrate uptake by eucalypt roots and associated proton fluxes measured using ion selective microelectrodes.
Author: Garnett, T.
Shabala, S.
Smethurst, P.
Newman, I.
Citation: Functional Plant Biology, 2003; 30(11):1165-1176
Publisher: C S I R O Publishing
Issue Date: 2003
ISSN: 1445-4408
Organisation: Australian Centre for Plant Functional Genomics (ACPFG)
Abstract: Ion-selective microelectrodes were used non-invasively to measure the concentration dependence of NH4+ and NO3– fluxes around the roots of intact solution-cultured Eucalyptus nitens (Deane & Maiden) Maiden. In addition, NH4+ and H+ fluxes were measured simultaneously at a range of NH4+ concentrations, and NO3– and H+ fluxes were measured simultaneously at a range of NO3– concentrations. Nitrogen concentrations ranged from 10–250 μM, i.e. in the range corresponding to the high affinity transport system (HATS). Both NH4+ and NO3– fluxes exhibited saturating Michaelis–Menten-style kinetics. The Km was 16 μM for NH4+ and 18 μM for NO3–. Values of V(max) were 53 nmol m–2 s–1 for NH4+ and 37 nmol m–2 s–1 for NO3–. Proton fluxes were highly correlated with NH4+ and NO3– fluxes, but the relationships were different. Proton efflux increased with increasing NH4+ concentration and mirrored the changing NH4+ fluxes. The ratio between NH4+ and H+ fluxes was 1 : –1.6. Proton influx was evident with initial exposure to NO3–, with the flux stoichiometry for NO3– : H+ being 1 : 1.4. Subsequent increases in NO3– concentration caused a gradual increase in H+ efflux such that the flux stoichiometry for NO3– : H+ became 1 : –0.8. The presence of 100 μM NH4+ greatly reduced NO3– fluxes and caused a large and constant H+ efflux. These results are evidence that E. nitens has a preference for NH4+ as a source of N, and that the fluxes of NH4+ and NO3– are quantitatively linked to H+ flux.
Keywords: ammonium; eucalyptus; ion fluxes; microelectrode; nitrate; proton
RMID: 0020081019
DOI: 10.1071/FP03087
Appears in Collections:Australian Centre for Plant Functional Genomics publications

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