Urea retranslocation from senescing Arabidopsis leaves is promoted by DUR3-mediated urea retrieval from leaf apoplast
Urea retranslocation from senescing Arabidopsis leaves is promoted by DUR3-mediated urea retrieval from leaf apoplast
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DOI：
10.1111/tpj.12740
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发表时间：
2015-02-01
期刊：
影响因子：
7.2
通讯作者：
von Wiren, Nicolaus
中科院分区：
文献类型：
--
作者：
Bohner, Anne;Kojima, Soichi;von Wiren, Nicolaus
在植物中，尿素来自于根的吸收或蛋白质的降解。虽然在衰老过程中会释放大量的尿素，但尿素主要被视为一种短暂的氮(N)分解代谢产物，用于尿素酶介导的氨水解。在这里，我们研究了DUR3和尿素在氮素再动员中的作用。在自然叶片衰老过程中，尿素浓度和DUR3转录本水平与OR1等衰老标记呈平行增加，且与植株年龄和叶龄相关。DUR3基因的缺失降低了尿素在叶片中的积累，但增加了尿素流失到叶质外体的比例。在自然衰老和缺氮诱导下，DUR3启动子在维管系统中的活性最高，但在周围的束鞘和叶肉细胞中也有表达。对野生型叶片叶柄分泌物的分析表明，来自尿素的氮占氨基酸氮的13%，在缺乏尿素酶活性的ureG-2缺失突变体中，衰老叶片的尿素输出量进一步增加。在du3ureG双插入系中，DUR3的缺失降低了叶柄的尿素输出。这些结果表明，尿素可以作为叶片衰老的早期代谢标志，DUR3介导的尿素回收有助于叶片衰老过程中尿素中氮素的重新转运。
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 dur3ureG 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.