In plants high affinity transport proteins mediate the essential transport of ammonium across membranes. In Arabidopsis thaliana six of these AMmonium Transporters (AMTs) are encoded by the genome. All of them show a unique expression pattern. While most AMTs are highly expressed in the root, AtAMT1;4 expression is limited to the pollen grains and the pollen tube. Here, we addressed the transport characteristics of AtAMT1;4 in the heterologous Xenopus laevis oocytes system. The transport saturated and showed high affinity for ammonium with a Km value lower than 10 µM. Based on our electrophysiological analysis, we classified AtAMT1;4 as a high affinity ammonium transporter.
