Three Functional Transporters for Constitutive, Diurnally Regulated, and Starvation-Induced Uptake of Ammonium into Arabidopsis Roots
- 1 May 1999
- journal article
- Published by Oxford University Press (OUP) in Plant Cell
- Vol. 11 (5), 937-947
- https://doi.org/10.1105/tpc.11.5.937
Abstract
Ammonium and nitrate are the prevalent nitrogen sources for growth and development of higher plants. 15N-uptake studies demonstrated that ammonium is preferred up to 20-fold over nitrate by Arabidopsis plants. To study the regulation and complex kinetics of ammonium uptake, we isolated two new ammonium transporter (AMT) genes and showed that they functionally complemented an ammonium uptake-deficient yeast mutant. Uptake studies with 14C-methylammonium and inhibition by ammonium yielded distinct substrate affinities between </=0.5 and 40 microM. Correlation of gene expression with 15NH4+ uptake into plant roots showed that nitrogen supply and time of day differentially regulated the individual carriers. Transcript levels of AtAMT1;1, which possesses an affinity in the nanomolar range, steeply increased with ammonium uptake in roots when nitrogen nutrition became limiting, whereas those of AtAMT1;3 increased slightly, with AtAMT1;2 being more constitutively expressed. All three ammonium transporters showed diurnal variation in expression, but AtAMT1;3 transcript levels peaked with ammonium uptake at the end of the light period, suggesting that AtAMT1;3 provides a link between nitrogen assimilation and carbon provision in roots. Our results show that high-affinity ammonium uptake in roots is regulated in relation to the physiological status of the plant at the transcriptional level and by substrate affinities of individual members of the AMT1 gene family.Keywords
This publication has 23 references indexed in Scilit:
- A Role for the AKT1 Potassium Channel in Plant NutritionScience, 1998
- The MEP2 ammonium permease regulates pseudohyphal differentiation in Saccharomyces cerevisiaeThe EMBO Journal, 1998
- A hidden Markov model for predicting transmembrane helices in protein sequences.1998
- Two glucose transporters in Saccharomyces cerevisiae are glucose sensors that generate a signal for induction of gene expression.Proceedings of the National Academy of Sciences of the United States of America, 1996
- Preferential expression of an ammonium transporter and of two putative nitrate transporters in root hairs of tomato.Proceedings of the National Academy of Sciences of the United States of America, 1996
- The Permeation of Ammonium through a Voltage-independent K + Channel in the Plasma Membrane of Rye RootsThe Journal of Membrane Biology, 1996
- Cloning and expression of the MEP1 gene encoding an ammonium transporter in Saccharomyces cerevisiae.The EMBO Journal, 1994
- An efficient transformation procedure enabling long‐term storage of competent cells of various yeast generaYeast, 1991
- Barley Mutants Lacking Chloroplast Glutamine Synthetase—Biochemical and Genetic AnalysisPlant Physiology, 1987
- A simple method for displaying the hydropathic character of a proteinJournal of Molecular Biology, 1982