title: Analysis of amino acid metabolism in the ear of maize mutants deficient in two cytosolic glutamine synthetase isoenzymes highlights the importance of asparagine for nitrogen translocation within sink organs.
abstract: Nitrogen (N) metabolism was characterized in the developing ear of glutamine synthetase deficient mutants (gln1-3, gln1-4 and gln1-3/gln1-4) of maize exhibiting a reduction in kernel yield. During the grain-filling period, the metabolite contents, enzyme activities and steady-state levels of transcripts for marker genes of amino acid synthesis and interconversion were monitored in the cob and kernels. The ear of gln1-3 and gln1-3/gln1-4 had a higher free amino acid content and a lower C/N ratio, when compared to the wild type. The free ammonium concentrations were also much higher in gln1-3/gln1-4, and Asn accumulation was higher in gln1-3 and gln1-3/gln1-4. The level of transcripts of ZmAS3 and ZmAS4, two genes encoding asparagine synthetase, increased in the 'aborted kernels' of gln1-3 and gln1-3/gln1-4. The results show that N metabolism is clearly different in developing and 'aborted kernels'. The data support the hypothesis that N accumulated in 'aborted kernels' is remobilized via the cob to developing kernels using Asn as a transport molecule. The two genes ZmAS3 and ZmAS4 are likely to play an important role during this process.
authors.affiliation: Unité de Nutrition Azotée des Plantes, Unité de Recherche 511, Institut Jean-Pierre Bourgin, Institut National de la Recherche Agronomique, Centre de Versailles-Grignon, Versailles Cedex, France.
authors.forename: Rafael A
authors.initials: RA
authors.lastname: Cañas
authors.forename: Isabelle
authors.initials: I
authors.lastname: Quilleré
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Lea
authors.forename: Bertrand
authors.initials: B
authors.lastname: Hirel
mesh_terms: D001216:Asparagine / Q000378:metabolism*; D001692:Biological Transport / Q000235:genetics / Q000502:physiology; D003600:Cytosol / Q000201:enzymology* / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000502:physiology; D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism*; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D003313:Zea mays / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism*
chemical_list: D007527:Isoenzymes; D010940:Plant Proteins; D001216:Asparagine; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen