title: Urea retranslocation from senescing Arabidopsis leaves is promoted by DUR3-mediated urea retrieval from leaf apoplast.
abstract: In plants, urea derives either from root uptake or protein degradation. Although large quantities of urea are released during senescence, urea is mainly seen as a short-lived nitrogen (N) catabolite serving urease-mediated hydrolysis to ammonium. Here, we investigated the roles of DUR3 and of urea in N remobilization. During natural leaf senescence urea concentrations and DUR3 transcript levels showed a parallel increase with senescence markers like ORE1 in a plant age- and leaf age-dependent manner. Deletion of DUR3 decreased urea accumulation in leaves, whereas the fraction of urea lost to the leaf apoplast was enhanced. Under natural and N deficiency-induced senescence DUR3 promoter activity was highest in the vasculature, but was also found in surrounding bundle sheath and mesophyll cells. An analysis of petiole exudates from wild-type leaves revealed that N from urea accounted for >13% of amino acid N. Urea export from senescent leaves further increased in ureG-2 deletion mutants lacking urease activity. In the dur3 ureG double insertion line the absence of DUR3 reduced urea export from leaf petioles. These results indicate that urea can serve as an early metabolic marker for leaf senescence, and that DUR3-mediated urea retrieval contributes to the retranslocation of N from urea during leaf senescence.
authors.affiliation: Department of Physiology & Cell Biology, Leibniz-Institute of Plant Genetics and Crop Plant Research, Corrensstr 3, D-06466, Gatersleben, Germany.
authors.forename: Anne
authors.initials: A
authors.lastname: Bohner
authors.forename: Soichi
authors.initials: S
authors.lastname: Kojima
authors.forename: Mohammad
authors.initials: M
authors.lastname: Hajirezaei
authors.forename: Michael
authors.initials: M
authors.lastname: Melzer
authors.forename: Nicolaus
authors.initials: N
authors.lastname: von Wirén
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D001692:Biological Transport / Q000235:genetics; D016922:Cellular Senescence; D009584:Nitrogen / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism / Q000502:physiology; D027981:Symporters / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014508:Urea / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; C474639:DUR3 protein, Arabidopsis; D027981:Symporters; D014508:Urea; D009584:Nitrogen
keywords: leaf senescence; nitrogen efficiency; phloem transport; urea metabolism; urea uptake; urease