The regulation of nitrate and ammonium transport systems in plants

Inorganic nitrogen concentrations in soil solutions vary across several orders of magnitude among different soils and as a result of seasonal changes. In order to respond to this heterogeneity, plants have evolved mechanisms to regulate \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({\mathrm{NO}_{3}^{{-}}}\) \end{document} and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({\mathrm{NH}_{4}^{{+}}}\) \end{document} influx. In addition, efflux analysis using 13N has revealed that there is a co‐ordinated regulation of all component fluxes within the root, including biochemical fluxes. Physiological studies have demonstrated the presence of two high‐affinity transporter systems (HATS) for \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({\mathrm{NO}_{3}^{{-}}}\) \end{document} and one HATS for \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({\mathrm{NH}_{4}^{{+}}}\) \end{document} in roots of higher plants. By contrast, in Arabidopsis thaliana there exist seven members of the NRT2 family encoding putative HATS for \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({\mathrm{NO}_{3}^{{-}}}\) \end{document} and five members of the AMT1 family encoding putative HATS for \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({\mathrm{NH}_{4}^{{+}}}\) \end{document}. The induction of high‐affinity \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({\mathrm{NO}_{3}^{{-}}}\) \end{document} transport and Nrt2.1 and Nrt2.2 expression occur in response to the provision of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({\mathrm{NO}_{3}^{{-}}}\) \end{document}, while down‐regulation of these genes appear to be due