尿素广泛存在于自然界中, 是易于被许多生物(如植物)利用的生长氮源。该文通过概述尿素在不同生命系统中存在的基础生理意义及各类型尿素转运蛋白, 讨论了植物细胞中尿素合成与分解的各种途径及尿素在植物氮营养、代谢和运输中的生理作用。迄今为止, 在植物中已发现了2类转运尿素的膜蛋白, 即MIPs和DUR3, 它们分别在低亲和力、高亲和力尿素运输中发挥潜在作用。异源表达结果表明, MIPs介导了尿素的被动迁移; 而AtDUR3则参与拟南芥根系对尿素的吸收。对MIPs和DUR3转运尿素的酶学特征、亚细胞作用位点和表达调控状况等的研究表明: 它们的分子生物学功能与植物的氮营养及氮素再分配和利用相关。

Urea occurs in nature and serves as a rapidly available nitrogen (N) source for the growth of many organisms, including pl-ants. This review gives a brief overview of the fundamental physiological significance of urea occurrence and its permeable proteins in various living systems. Mechanisms for urea generation and degradation in plants are discussed, and physiolo-gical roles of urea in plant N nutrition, metabolism and transport are highlighted. Two types of plant membrane transporters, namely MIPs and DUR3, potentially play roles in low- and high-affinity urea transport, respectively. MIPs mediate passive urea movement and were primarily investigated in heterologous gene-expression systems; AtDUR3 was shown to particip-ate in urea uptake in Arabidopsis roots. Transport characteristics, transcriptional regulation, and the subcellular localization of MIPs and DUR3 suggest the relevance of urea transport through these transporters in N nutrition and redistribution in planta.