title: Response to nitrate/ammonium nutrition of tomato (Solanum lycopersicum L.) plants overexpressing a prokaryotic NH4(+)-dependent asparagine synthetase.
abstract: Nitrogen availability is an important limiting factor for plant growth. Although NH4(+) assimilation is energetically more favorable than NO3(-), it is usually toxic for plants. In order to study if an improved ammonium assimilatory metabolism could increase the plant tolerance to ammonium nutrition, tomato (Solanum lycopersicum L. cv P-73) plants were transformed with an NH4(+)-dependent asparagine synthetase (AS-A) gene from Escherichia coli (asnA) under the control of a PCpea promoter (pea isolated constitutive promotor). Homozygous (Hom), azygous (Az) asnA and wild type (WT) plants were grown hydroponically for 6 weeks with normal Hoagland nutrition (NO3(-)/NH4(+)=6/0.5) and high ammonium nutrition (NO3(-)/NH4(+)=3.5/3). Under Hoagland's conditions, Hom plants produced 40-50% less biomass than WT and Az plants. However, under NO3(-)/NH4(+)=3.5/3 the biomass of Hom was not affected while it was reduced by 40-70% in WT and Az plants compared to Hoagland, respectively. The Hom plants accumulated 1.5-4 times more asparagine, glycine, serine and soluble proteins and registered higher glutamine synthetase (GS) and glutamate synthase (GOGAT) activities in the light-adapted leaves than the other genotypes, but had similar NH4(+) and NO3(-) levels in all conditions. In the dark-adapted leaves, a protein catabolism occurred in the Hom plants with a concomitant 25-40% increase in organic acid concentration, while asparagine accumulation registered the highest values. The aforementioned processes might be responsible for a positive energetic balance as regards the futile cycle of the transgenic protein synthesis and catabolism. This explains growth penalty under standard nutrition and growth stability under NO3(-)/NH4(+)=3.5/3, respectively.
authors: Departamento de Nutrición Vegetal, Centro de Edafología y Biología Aplicada del Segura (CEBAS), Consejo Superior de Investigaciones Científicas (CSIC), Campus Universitario de Espinardo, E-30100, Murcia, Spain. cmandujar@cebas.csic.es
authors: Cristina
authors: C
authors: Martínez-Andújar
authors: Michel Edmond
authors: ME
authors: Ghanem
authors: Alfonso
authors: A
authors: Albacete
authors: Francisco
authors: F
authors: Pérez-Alfocea
mesh_terms: D000596:Amino Acids / Q000032:analysis; D001216:Asparagine / Q000032:analysis; D001217:Aspartate-Ammonia Ligase / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D018533:Biomass; D002241:Carbohydrates / Q000032:analysis; D002264:Carboxylic Acids / Q000032:analysis; D019069:Cell Respiration; D002734:Chlorophyll / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D008027:Light; D018551:Solanum lycopersicum / Q000201:enzymology / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D009566:Nitrates / Q000378:metabolism*; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D018517:Plant Roots / Q000201:enzymology / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D018520:Plant Shoots / Q000201:enzymology / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D030821:Plants, Genetically Modified; D011188:Potassium / Q000032:analysis; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; D002241:Carbohydrates; D002264:Carboxylic Acids; D009566:Nitrates; D000644:Quaternary Ammonium Compounds; D002734:Chlorophyll; D001216:Asparagine; D001217:Aspartate-Ammonia Ligase; D011188:Potassium