AtAMT1 gene expression and NH4+ uptake in roots of Arabidopsis thaliana: evidence for regulation by root glutamine levels

• Published in: The Plant journal : for cell and molecular biology 1999-07, Vol.19 (2), p.143-152
• Main Authors: Rawat, S.R, Silim, S.N, Kronzucker, H.J, Siddiqi, M.Y, Glass, A.D.M
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; ammonium compounds; ammonium nitrate; Arabidopsis - drug effects; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis thaliana; Biological and medical sciences; Biological Transport - drug effects; Carrier Proteins - genetics; Cation Transport Proteins; Cell Membrane - metabolism; chemical constituents of plants; cytoplasm; Cytoplasm - metabolism; Economic plant physiology; Fundamental and applied biological sciences. Psychology; gene expression; Gene Expression Regulation, Plant; genes; genetic regulation; glutamine; Glutamine - metabolism; messenger RNA; Metabolism; Nitrates - pharmacology; Nitrogen metabolism; Nitrogen metabolism and other ones (excepting carbon metabolism); nutrient availability; nutrient deficiencies; nutrient uptake; Nutrition. Photosynthesis. Respiration. Metabolism; Plant physiology and development; Plant Proteins; Plant Roots - metabolism; Quaternary Ammonium Compounds - metabolism; Quaternary Ammonium Compounds - pharmacokinetics; RNA, Messenger - drug effects; RNA, Messenger - metabolism; roots; Time Factors; Transcription, Genetic
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1046/j.1365-313X.1999.00505.x

The mechanisms involved in regulating high-affinity ammonium (NH(4)+) uptake and the expression of the AtAMT1 gene encoding a putative high-affinity NH(4)+ transporter were investigated in the roots of Arabidopsis thaliana. Under conditions of steady-state nitrogen (N) supply, transcript levels of the AtAMT1 gene and V(max) values for high-affinity (13)NH(4)+ influx were inversely correlated with levels of N provision. Following resupply of NH(4)NO(3) to N-starved plants, AtAMT1 mRNA levels and (13)NH(4)+ influx declined rapidly but remained high when the conversion of NH(4)+ to glutamine (Gln) was blocked with methionine sulfoximine (MSX). This result demonstrates that end products of NH(4)+ assimilation, rather than NH(4)+ itself, are responsible for regulating AtAMT1 gene expression. Consistent with this hypothesis, AtAMT1 gene expression and NH(4)+ influx were suppressed by provision of Gln alone, or together with NH(4)NO(3) plus MSX. Furthermore, AtAMT1 transcript levels and (13)NH(4)+ influx were negatively correlated with root Gln concentrations, following resupply of N to N-starved plants. In addition to this level of control, the data suggest that high cytoplasmic [NH(4)+] may inhibit NH(4)+ influx.