Nitrogen depletion enhances endodermal suberization without restricting transporter-mediated root NO₃^- influx

Roots vary their permeability to aid radial transport of solutes towards xylem vessels in response to nutritional cues. Nitrogen (N) depletion was previously shown to induce early suberization of endodermal cell walls and reduce hydraulic conductivity of barley roots suggesting reduced apoplastic transport of ions (Armand et al., 2019). Suberization may also limit transcellular ion movement by blocking access to transporters (Barberon et al., 2016). The aim of this study was to confirm that N depletion induced suberization in the roots of barley and demonstrate that this was a specific effect in response to NO₃^- depletion. Furthermore, in roots with early and enhanced suberization, we assessed their ability for transporter-mediated NO₃^- influx. N depletion induced lateral root elongation and early and enhanced endodermal suberization of the seminal root of each genotype. Both root to shoot NO₃^- translocation and net N uptake was half that of plants supplied with steady-state NO₃^-. Genes with predicted functions in suberin synthesis (HvHORST) and NO₃^- transport (HvNRT2.2) were induced under N-deplete conditions. N-deplete roots had a higher capacity for high-affinity NO₃^- influx in early suberized roots than under optimal NO₃^-. In conclusion, NO₃^- depletion induced early and enhanced suberization in the roots of barley, however, suberization did not restrict transcellular NO₃^- transport.