Abstract
The study of ammonium (NH4 +) transport across plant cell membranes requires accurate measurement of NH4 + gradients across subcellular gradients. We have developed an ammonium-selective microelectrode based on the ionophore nonactin. This electrode can detect NH4 + activities (aNH4) in vivo in the millimolar range in the presence of cytosolic levels of potassium, the main interfering ion. The electrode was used to measure intracellular aNH4 in internodal cells of the giant alga Chara corallina. Results from cells incubated in media supplemented with 1 mM NH4 + produced two populations, with means of 7.3 and 30.8 mM, respectively. HPLC analysis of vacuolar sap suggests the higher population represents vacuolar impalements, and the lower population can thus be assumed to be cytosolic. These results suggest a four-fold accumulation of NH4 + in the vacuolar compartment of Chara.
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References
Henriksen G H, Bloom A J and Spanswick R M 1990 Measurement of net fluxes of ammonium and nitrate at the surface of barley roots using ion-selective microelectrodes. Plant Physiol. 93, 271–280.
IUPAC 1994 Recommendations for the nomenclature of ionselective electrodes (IUPAC recommendations 1994). Pure & Appl. Chem. 66, 2528–2536.
Kronzucker H J, Siddiqi MY and Glass A DM 1995 Compartmentation and flux characteristics of ammonium in spruce. Planta 196, 691–698.
Miller A J and Zhen R-G. 1991 Measurement of intracellular nitrate concentrations in Chara using nitrate-selective microelectrodes. Planta 184, 47–52.
Ryan P R and Walker N A 1994 The regulation of ammonia uptake in Chara australis. J Exp. Bot. 45, 1057–1067.
Scholer R P and Simon W1970 Antibiotika-Membranelektrode zur selektiven Erfassung von Ammoniumionenaktivitäten. Chimia 24, 372–374.
Tyerman S, Whitehead L F and Day D A 1995 A channel-like transporter for NH4 + on the symbiotic interface of N2-fixing plants. Nature 378, 629–632.
Walker D J, Smith S J and Miller A J 1995 Simultaneous measurement of intracellular pH and K+ or NO3 _ in barley root cells using triple-barreled, ion-selective microelectrodes. Plant Physiol. 108, 743–751.
Walker D J, Leigh R A and Miller A J 1996 Potassium homeostasis in vacuolate plant cells. Proc. Natl. Acad. Sci. USA 93, 10510–10514.
Wang M Y, Siddiqi M Y, Ruth T J and Glass A D M 1993 Ammonium uptake by rice roots. I. Fluxes and subcellular distribution of 13NH4 +. Plant Physiol. 103, 1249–1258.
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Wells, D.M., Miller, A.J. Intracellular measurement of ammonium in Chara corallina using ion-selective microelectrodes. Plant and Soil 221, 103–106 (2000). https://doi.org/10.1023/A:1004767518004
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DOI: https://doi.org/10.1023/A:1004767518004