Urea is the most used nitrogenous fertilizer worldwide and an important nitrogen-containing plant metabolite. Despite its major use as fertilizer, its direct uptake is limited due to the ubiquitous presence of bacterial urease, which leads to the formation of ammonium. In this review, we will focus mainly on the more recent research about the high-affinity urea transporter function in nitrogen-deficient conditions. The effective use of nitrogenous compounds is essential for plants to be able to deal with nitrogen-deficient conditions. Leaf senescence, either induced by development and/or by nitrogen deficiency, plays an important role in the efficient use of already assimilated nitrogen. Proteinaceous nitrogen is set free through catabolic reactions: the released amino acids from protein catabilization are in turn catabolized leading to an accumulation of ammonium and urea. The concentration and conversion to transportable forms of nitrogen, e.g. amino acids like glutamine and asparagine, are coordinated around the vascular tissue. Urea itself can be translocated directly over the phloem by a mechanism that involves DUR3, or it is converted by urease to ammonium and assimilated again into amino acids. The details of the high-affinity transporter function in this physiological context and the implications for crop yield are explained. This article is protected by copyright. All rights reserved.

中文翻译：

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高亲和力尿素转运蛋白在缺氮条件下的功能

尿素是世界上使用最广泛的氮肥，也是一种重要的含氮植物代谢物。尽管它主要用作肥料，但由于细菌脲酶的普遍存在，它的直接吸收受到限制，这会导致铵的形成。在这篇综述中，我们将主要关注关于缺氮条件下高亲和力尿素转运蛋白功能的最新研究。有效利用含氮化合物对于植物能够应对缺氮条件至关重要。由发育和/或氮缺乏引起的叶片衰老在有效利用已经吸收的氮方面起着重要作用。蛋白质氮通过分解代谢反应释放：蛋白质分解释放的氨基酸依次被分解代谢，导致铵和尿素的积累。氮的浓度和转化为可运输形式的氮，例如像谷氨酰胺和天冬酰胺这样的氨基酸，在血管组织周围进行协调。尿素本身可以通过涉及 DUR3 的机制直接转移到韧皮部，或者它被尿素酶转化为铵并再次同化为氨基酸。解释了这种生理背景下高亲和力转运蛋白功能的细节以及对作物产量的影响。本文受版权保护。版权所有。尿素本身可以通过涉及 DUR3 的机制直接转移到韧皮部，或者它被尿素酶转化为铵并再次同化为氨基酸。解释了这种生理背景下高亲和力转运蛋白功能的细节以及对作物产量的影响。本文受版权保护。版权所有。尿素本身可以通过涉及 DUR3 的机制直接转移到韧皮部，或者它被尿素酶转化为铵并再次同化为氨基酸。解释了这种生理背景下高亲和力转运蛋白功能的细节以及对作物产量的影响。本文受版权保护。版权所有。