No abstract

Most plants use nitrate (NO3-) as their major nitrogen (N) source. The NO3- uptake capacity of a plant is determined by three interdependent factors that are sensitive to NO3- availability: (i) the functional properties of the transporters in roots that contribute to the acquisition of NO3- from the external medium, (ii) the density of functional transporters at the plasma membrane of root cells, and (iii) the surface and architecture of the root system. The identification of factors that regulate the NO3--sensing systems is important for both fundamental and applied science, because these factors control the capacity of plants to use the available NO3-, a process known as the “nitrate use efficiency.” The molecular component of the transporters involved in uptake and sensing mechanism in Arabidopsis roots are presented and their relative contribution discussed.

N-fixing nodules are new organs formed on legume roots as a result of the beneficial interaction with soil bacteria, rhizobia. The nodule functioning is still a poorly characterized step of the symbiotic interaction, as only a few of the genes induced in N-fixing nodules have been functionally characterized. We present here the characterization of a member of the nitrate transporter1/peptide transporter family, The phenotypic characterization carried out in independent LORE1 insertion lines indicates a positive role of LjNPF8.6 on nodule functioning, as knockout mutants display N-fixation deficiency (25%) and increased nodular superoxide content. The partially compromised nodule functioning induces two striking phenotypes: anthocyanin accumulation already displayed 4 weeks after inoculation and shoot biomass deficiency, which is detected by long-term phenotyping. LjNPF8.6 achieves nitrate uptake in oocytes at both 0.5 and 30 mm external concentrations, and a possible role as a nitrate transporter in the control of N-fixing nodule activity is discussed.