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Plant Cell Physiol. 2013 Sep;54(9):1515-24. doi: 10.1093/pcp/pct099. Epub 2013 Jul 5.

Characterization of AMT-mediated high-affinity ammonium uptake in roots of maize (Zea mays L.).

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  • 1Department of Plant Nutrition, Key Laboratory of Plant-Soil Interactions, MOE, Center for Resources, Environment and Food Security, China Agricultural University, Beijing 100193, China.

Abstract

High-affinity ammonium uptake in plant roots is mainly mediated by AMT1-type ammonium transporters, and their regulation varies depending on the plant species. In this study we aimed at characterizing AMT-mediated ammonium transport in maize, for which ammonium-based fertilizer is an important nitrogen (N) source. Two ammonium transporter genes, ZmAMT1;1a and ZmAMT1;3, were isolated from a maize root-specific cDNA library by functional complementation of an ammonium uptake-defective yeast mutant. Ectopic expression of both genes in an ammonium uptake-defective Arabidopsis mutant conferred high-affinity ammonium uptake capacities in roots with substrate affinities of 48 and 33 μM for ZmAMT1;1a and ZmAMT1;3, respectively. In situ hybridization revealed co-localization of both ZmAMT genes on the rhizodermis, suggesting an involvement in capturing ammonium from the rhizosphere. In N-deficient maize roots, influx increased significantly while ZmAMT expression did not. Ammonium resupply to N-deficient or nitrate-pre-cultured roots, however, rapidly enhanced both influx and ZmAMT transcript levels, revealing a substrate-inducible regulation of ammonium uptake. In conclusion, the two rhizodermis-localized transporters ZmAMT1;1a and ZmAMT1;3 are most probably the major components in the high-affinity transport system in maize roots. A particular regulatory feature is their persistent induction by ammonium rather than an up-regulation under N deficiency.

KEYWORDS:

AMT; High-affinity ammonium uptake; Maize roots; Membrane transport; Nitrogen nutrition; Transcriptional regulation

PMID:
23832511
[PubMed - indexed for MEDLINE]
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