Characterization of Arabidopsis AtAMT2, a High-Affinity Ammonium Transporter of the Plasma Membrane

• Published in: Plant physiology (Bethesda) Vol. 130; no. 4; pp. 1788 - 1796
• Main Authors: Christian Sohlenkamp, Craig C. Wood, Gerhard W. Roeb, Udvardi, Michael K.
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Biologists 01.12.2002; American Society of Plant Physiologists
• Subjects: Ammonium; Ammonium nitrate; Arabidopsis; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis thaliana; beta-glucuronidase; Biochemical Processes and Macromolecular Structures; Biological and medical sciences; Carrier Proteins; Carrier Proteins - genetics; Carrier Proteins - metabolism; Cation Transport Proteins; Cell Membrane; Cell Membrane - genetics; Cell Membrane - metabolism; Cell membranes; Cell physiology; chemical constituents of plants; drug effects; Epidermal cells; Fundamental and applied biological sciences. Psychology; gene expression; gene expression regulation; Gene Expression Regulation, Plant; Gene Expression Regulation, Plant - drug effects; genetics; Glucuronidase; Glucuronidase - genetics; Glucuronidase - metabolism; green fluorescent protein; Green Fluorescent Proteins; isotope labeling; Kinetics; Leaves; Luminescent Proteins; Luminescent Proteins - genetics; Luminescent Proteins - metabolism; membrane proteins; messenger RNA; metabolism; Nitrates; Nitrates - pharmacology; nitrogen; nutrient uptake; pharmacology; photorespiration; Plant growth; plant morphology; Plant physiology and development; plant proteins; Plant Proteins - genetics; Plant Proteins - metabolism; Plant roots; plant tissues; Plants; Plants, Genetically Modified; plasma membrane; Plasma membrane and permeation; potassium nitrate; promoter regions; Quaternary Ammonium Compounds; Quaternary Ammonium Compounds - metabolism; Quaternary Ammonium Compounds - pharmacology; radionuclides; Recombinant Fusion Proteins; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; reporter genes; RNA; Saccharomyces cerevisiae; small interfering RNA; transcription (genetics); Yeasts; Ammonium; Membrane protein; Nutrition; Cell permeability; Ionic channel; Gene expression; Arabidopsis thaliana; Characterization; Regulation(control); Absorption; Cruciferae; Dicotyledones; Angiospermae; Plasma membrane; Spermatophyta; Experimental plant; Catalyst activity; Carrier protein
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.008599

AtAMT2 is an ammonium transporter that is only distantly related to the five members of the AtAMT1 family of high-affinity ammonium transporters in Arabidopsis. The short-lived radioactive ion ^{13}\text{NH}{}_{4}^{+}$ was used to show that AtAMT2, expressed in yeast (Saccharomyces cerevisiae), is a high-affinity transporter with a Km for ammonium of about 20 μM. Changes in external pH between 5.0 and 7.5 had little effect on the Km for ammonium, indicating that NH4 +, not NH3, is the substrate for AtAMT2. The AtAMT2 gene was expressed in all organs of Arabidopsis and was subject to nitrogen (N) regulation, at least in roots where expression was partially repressed by high concentrations of ammonium nitrate and derepressed in the absence of external N. Although expression of AtAMT2 in shoots responded little to changes in root N status, transcript levels in leaves declined under high CO2 conditions. Transient expression of an AtAMT2-green fluorescent protein fusion protein in Arabidopsis leaf epidermal cells indicated a plasma membrane location for the AtAMT2 protein. Thus, AtAMT2 is likely to play a significant role in moving ammonium between the apoplast and symplast of cells throughout the plant. However, a dramatic reduction in the level of AtAMT2 transcript brought about by dsRNA interference with gene expression had no obvious effect on plant growth or development, under the conditions tested.