Document Detail

Respective roles of the glutamine synthetase/glutamate synthase cycle and glutamate dehydrogenase in ammonium and amino acid metabolism during germination and post-germinative growth in the model legume Medicago truncatula.
MedLine Citation:
PMID:  14991406     Owner:  NLM     Status:  MEDLINE    
Our objective was to determine the respective roles of the couple glutamine synthetase/glutamate synthase (GS/GOGAT) and glutamate dehydrogenase (GDH) in ammonium and amino acid metabolism during germination and post-germinative growth in the model legume Medicago truncatula Gaertn. For this aim, amino acids were analyzed by HPLC and changes in gene expression of several enzymes involved in N and C metabolism were studied by real-time quantitative reverse transcription-polymerase chain reaction. Among the enzymes studied, GDH showed the highest increase in gene expression (80-fold), specifically in the embryo axis and concomitant with the increase in ammonium content during post-germinative growth. In cotyledons, GDH gene expression was very low. Although in vitro GDH aminating activity was several times higher than its deaminating activity, in vivo 15NH4 incorporation into amino acids was completely inhibited by methionine sulfoximine, a GS inhibitor, indicating that GDH is not involved in ammonium assimilation/detoxification. Changes in the expressions of GS and GOGAT isoforms revealed that GS1b (EC in concert with NADH-dependent GOGAT (EC constitute the major route of assimilation of ammonium derived from reserve mobilization and glutamic acid/glutamine synthesis in germinating M. truncatula seeds. However, during post-germinative growth, although germination was held in darkness, expression of GS2 and Fd-GOGAT (EC increased and expression of GS1b decreased in cotyledons but not in the embryo axis. 2-Oxoglutarate, the substrate of the transamination reaction, was provided by the cytosolic isoform of isocitrate dehydrogenase (EC We suggest that GDH during post-germinative growth, specifically in the developing embryo axis, contributes to ammonium delivery to GS for glutamine synthesis in the absence of primary NO3- assimilation. Interestingly, this reaction also produces reducing power (NADH) in organs deprived of photosynthesis.
Gaëlle Glevarec; Sophie Bouton; Emmanuel Jaspard; Marie-Thérèse Riou; Jean-Bernard Cliquet; Akira Suzuki; Anis M Limami
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Publication Detail:
Type:  Journal Article     Date:  2004-02-26
Journal Detail:
Title:  Planta     Volume:  219     ISSN:  0032-0935     ISO Abbreviation:  Planta     Publication Date:  2004 Jun 
Date Detail:
Created Date:  2004-06-01     Completed Date:  2004-08-31     Revised Date:  2005-11-17    
Medline Journal Info:
Nlm Unique ID:  1250576     Medline TA:  Planta     Country:  Germany    
Other Details:
Languages:  eng     Pagination:  286-97     Citation Subset:  IM    
Copyright Information:
Copyright 2004 Springer-Verlag
UMR INRA 1191, Physiologie Moléculaire des semences, University of Angers, 2 Bd Lavoisier, 49045 Angers cedex 01, France.
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MeSH Terms
Carbon / metabolism
Cotyledon / chemistry,  enzymology,  metabolism
Culture Media
Gene Expression
Glutamate Dehydrogenase / physiology*
Glutamate Synthase / physiology*
Glutamate-Ammonia Ligase / physiology*
Medicago / enzymology,  growth & development*,  metabolism
Nitrogen / metabolism
Quaternary Ammonium Compounds / metabolism*
Reverse Transcriptase Polymerase Chain Reaction
Seeds / enzymology,  growth & development
Time Factors
Reg. No./Substance:
0/Culture Media; 0/Quaternary Ammonium Compounds; 7440-44-0/Carbon; 7727-37-9/Nitrogen; EC Synthase; EC Dehydrogenase; EC Ligase

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