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https://hdl.handle.net/2440/44901
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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: an international journal of plant function, 2003; 30(11):1165-1176 |
Publisher: | C S I R O Publishing |
Issue Date: | 2003 |
ISSN: | 1445-4408 1445-4416 |
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 |
DOI: | 10.1071/FP03087 |
Published version: | http://dx.doi.org/10.1071/fp03087 |
Appears in Collections: | Aurora harvest 6 Australian Centre for Plant Functional Genomics publications |
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