title: Ammonium formation and assimilation in P(SARK)∷IPT tobacco transgenic plants under low N.
abstract: Wild Type (WT) and transgenic tobacco plants expressing isopentenyltransferase (IPT), a gene encoding the enzyme regulating the rate-limiting step in cytokinins (CKs) synthesis, were grown under limited nitrogen (N) conditions. We analyzed nitrogen forms, nitrogen metabolism related-enzymes, amino acids and photorespiration related-enzymes in WT and P(SARK)∷IPT tobacco plants. Our results indicate that the WT plants subjected to N deficiency displayed reduced nitrate (NO₃⁻) assimilation. However, an increase in the production of ammonium (NH₄⁺), by the degradation of proteins and photorespiration led to an increase in the glutamine synthetase/glutamate synthase (GS/GOGAT) cycle in WT plants. In these plants, the amounts of amino acids decreased with N deficiency, although the relative amounts of glutamate and glutamine increased with N deficiency. Although the transgenic plants expressing P(SARK)∷IPT and growing under suboptimal N conditions displayed a significant decline in the N forms in the leaf, they maintained the GS/GOGAT cycle at control levels. Our results suggest that, under N deficiency, CKs prevented the generation and assimilation of NH₄⁺ by increasing such processes as photorespiration, protein degradation, the GS/GOGAT cycle, and the formation of glutamine.
authors.affiliation: Department of Plant Physiology, Faculty of Science, Universidad de Granada, 18071 Granada, Spain. mmrubio@ugr.es
authors.forename: María del Mar
authors.initials: Mdel M
authors.lastname: Rubio-Wilhelmi
authors.forename: Eva
authors.initials: E
authors.lastname: Sanchez-Rodriguez
authors.forename: Miguel Angel
authors.initials: MA
authors.lastname: Rosales
authors.forename: Begoña
authors.initials: B
authors.lastname: Blasco
authors.forename: Juan Jose
authors.initials: JJ
authors.lastname: Rios
authors.forename: Luis
authors.initials: L
authors.lastname: Romero
authors.forename: Eduardo
authors.initials: E
authors.lastname: Blumwald
authors.forename: Juan Manuel
authors.initials: JM
authors.lastname: Ruiz
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000235:genetics / Q000378:metabolism; D000594:Amino Acid Oxidoreductases / Q000378:metabolism; D000596:Amino Acids / Q000096:biosynthesis; D018506:Gene Expression Regulation, Plant; D014644:Genetic Variation; D005838:Genotype; D005970:Glutamate Synthase / Q000378:metabolism; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D050901:Nitrate Reductase / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D010788:Photosynthesis / Q000235:genetics; D010937:Plant Growth Regulators / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism*; D059748:Proteolysis; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D009566:Nitrates; D010937:Plant Growth Regulators; D000644:Quaternary Ammonium Compounds; D000594:Amino Acid Oxidoreductases; D005970:Glutamate Synthase; D050901:Nitrate Reductase; D019883:Alkyl and Aryl Transferases; C024274:adenylate isopentenyltransferase; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen