title: Characterization of a developmental root response caused by external ammonium supply in Lotus japonicus.
abstract: Plants respond to changes of nutrient availability in the soil by modulating their root system developmental plan. This response is mediated by systemic changes of the nutritional status and/or by local perception of specific signals. The effect of nitrate on Arabidopsis (Arabidopsis thaliana) root development represents a paradigm of these responses, and nitrate transporters are involved both in local and systemic control. Ammonium (NH(4)(+)) represents an important nitrogen (N) source for plants, although toxicity symptoms are often associated with high NH(4)(+) concentration when this is present as the only N source. The reason for these effects is still controversial, and mechanisms associating ammonium supply and plant developmental programs are completely unknown. We determined in Lotus japonicus the range of ammonium concentration that significantly inhibits the elongation of primary and lateral roots without affecting the biomass of the shoot. The comparison of the growth phenotypes in different N conditions indicated the specificity of the ammonium effect, suggesting that this was not mediated by assimilatory negative feedback mechanisms. In the range of inhibitory NH(4)(+) conditions, only the LjAMT1;3 gene, among the members of the LjAMT1 family, showed a strong increased transcription that was reflected by an enlarged topology of expression. Remarkably, the short-root phenotype was phenocopied in transgenic lines by LjAMT1;3 overexpression independently of ammonium supply, and the same phenotype was not induced by another AMT1 member. These data describe a new plant mechanism to cope with environmental changes, giving preliminary information on putative actors involved in this specific ammonium-induced response.
authors.affiliation: Institute of Genetics and Biophysics, Naples, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Rogato
authors.forename: Enrica
authors.initials: E
authors.lastname: D'Apuzzo
authors.forename: Ani
authors.initials: A
authors.lastname: Barbulova
authors.forename: Selim
authors.initials: S
authors.lastname: Omrane
authors.forename: Aurora
authors.initials: A
authors.lastname: Parlati
authors.forename: Simona
authors.initials: S
authors.lastname: Carfagna
authors.forename: Alex
authors.initials: A
authors.lastname: Costa
authors.forename: Fiorella
authors.initials: F
authors.lastname: Lo Schiavo
authors.forename: Sergio
authors.initials: S
authors.lastname: Esposito
authors.forename: Maurizio
authors.initials: M
authors.lastname: Chiurazzi
mesh_terms: D000596:Amino Acids / Q000032:analysis; D018533:Biomass; D018506:Gene Expression Regulation, Plant; D000070116:Lotus / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D010641:Phenotype; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D018520:Plant Shoots / Q000254:growth & development; D030821:Plants, Genetically Modified / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D014158:Transcription, Genetic
chemical_list: D000596:Amino Acids; D000644:Quaternary Ammonium Compounds