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Urea retranslocation from senescing Arabidopsis leaves is promoted by DUR 3‐mediated urea retrieval from leaf apoplast
Author(s) -
Bohner Anne,
Kojima Soichi,
Hajirezaei Mohammad,
Melzer Michael,
Wirén Nicolaus
Publication year - 2015
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.12740
Subject(s) - urea , senescence , apoplast , urease , ammonium , biochemistry , chemistry , arabidopsis , biology , botany , mutant , cell wall , microbiology and biotechnology , gene , organic chemistry
Summary 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 DUR 3 and of urea in N remobilization. During natural leaf senescence urea concentrations and DUR 3 transcript levels showed a parallel increase with senescence markers like ORE 1 in a plant age‐ and leaf age‐dependent manner. Deletion of DUR 3 decreased urea accumulation in leaves, whereas the fraction of urea lost to the leaf apoplast was enhanced. Under natural and N deficiency‐induced senescence DUR 3 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 DUR 3 reduced urea export from leaf petioles. These results indicate that urea can serve as an early metabolic marker for leaf senescence, and that DUR 3‐mediated urea retrieval contributes to the retranslocation of N from urea during leaf senescence.