title: Nitric oxide controls nitrate and ammonium assimilation in Chlamydomonas reinhardtii.
abstract: Nitrate and ammonium are major inorganic nitrogen sources for plants and algae. These compounds are assimilated by means of finely regulated processes at transcriptional and post-translational levels. In Chlamydomonas, the expression of several genes involved in high-affinity ammonium (AMT1.1, AMT1.2) and nitrate transport (NRT2.1) as well as nitrate reduction (NIA1) are downregulated by ammonium through a nitric oxide (NO)-dependent mechanism. At the post-translational level, nitrate/nitrite uptake and nitrate reductase (NR) are also inhibited by ammonium, but the mechanisms implicated in this regulation are scarcely known. In this work, the effect of NO on nitrate assimilation and the high-affinity ammonium uptake was addressed. NO inhibited the high-affinity uptake of ammonium and nitrate/nitrite, as well as the NR activity, in a reversible form. In contrast, nitrite reductase and glutamine synthetase activities were not affected. The in vivo and in vitro studies suggested that NR enzyme is inhibited by NO in a mediated process that requires the cell integrity. These data highlight a role of NO in inorganic nitrogen assimilation and suggest that this signalling molecule is an important regulator for the first steps of the pathway.
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Universidad de Córdoba, Campus de Excelencia Agroalimentario CeiA3, Campus de Rabanales, Edificio Severo Ochoa, Córdoba 14071, Spain.
authors.forename: Emanuel
authors.initials: E
authors.lastname: Sanz-Luque
authors.forename: Francisco
authors.initials: F
authors.lastname: Ocaña-Calahorro
authors.forename: Angel
authors.initials: A
authors.lastname: Llamas
authors.forename: Aurora
authors.initials: A
authors.lastname: Galvan
authors.forename: Emilio
authors.initials: E
authors.lastname: Fernandez
mesh_terms: D016825:Chlamydomonas reinhardtii / Q000187:drug effects* / Q000378:metabolism*; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism*; D009569:Nitric Oxide / Q000494:pharmacology*; D009572:Nitrite Reductases / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*
chemical_list: D009566:Nitrates; D009573:Nitrites; D000644:Quaternary Ammonium Compounds; D009569:Nitric Oxide; D009572:Nitrite Reductases; D005974:Glutamate-Ammonia Ligase
keywords: Ammonium uptake; Chlamydomonas; glutamine synthetase; nitrate and nitrite uptake; nitrate reductase; nitric oxide; nitrite reductase; post-translational regulation.