高等植物Na+ 吸收、转运及细胞内Na+ 稳态平衡研究进展

盐胁迫是影响农业生产的重要环境因素之一。本文对植物Na+吸收的机制和途径、Na+在植物体内的长距离转运以及细胞内Na+稳态平衡的研究进展进行了概述。参与植物Na+吸收与转运的蛋白和通道可能包括HKT、LCT1、AKT和NSCC等。其中, HKT是植物体内普遍存在的一类转运蛋白, 能够介导Na+的吸收, 其结构中的带电氨基酸残基对于其离子选择性有着非常明显的影响。LCT1是从小麦中发现的一类能够介导低亲和性阳离子吸收的蛋白, 然而在典型的土壤Ca2+浓度下LCT1并不能发挥吸收Na+的功能。AKT家族的成员在高盐环境下可能也参与了Na+的吸收。目前虽然还没有克隆到编码NSCC蛋白的基因, 但是NSCC作为植物吸收Na+的主要途径的观点已被广泛接受。SOS1和HKT参与了Na+在根部与植株地上部的长距离转运过程, 它们在木质部和韧皮部的Na+装载和卸载中发挥重要作用, 从而影响植物的抗盐性。另外, 由质膜Na+/H+逆向转运蛋白SOS1、蛋白激酶SOS2以及Ca2+结合蛋白SOS3组成的SOS复合体对细胞的Na+稳态具有重要的调节作用, 单子叶和双子叶植物之间的这种调节机制在结构和功能上具有保守性。SOS复合体与其它位于质膜或液泡膜上的Na+/H+逆向转运蛋白以及H+泵一起调节着细胞的Na+稳态。

Advances in Study of Na+ Uptake and Transport in Higher Plants and Na+ Homeostasis in the Cell

Salt stress is one of the factors that influence agriculture productivity. In this paper, we review transporters and channels such as HKT, LCT1, AKT and NSCC possibly involved in plant Na+ uptake, as well as long-distance Na+ transport in plants and Na+ homeostasis in the cell. HKTs are ubiquitous transporters mediating Na+ uptake, whereby the charged amino acid residues play a pivotal role in cation selectivity. LCT1 is a novel transporter found in wheat that can mediate low-affinity cation uptake but does not function in Na+ uptake at typical soil Ca2+ concentrations. AKTs, another family of transporters, may also be involved in Na+ uptake under high salinity. Although no gene encoding NSCC has been cloned, NSCCs are considered the main pathway though which plants take up excessive Na+. SOS1 and HKT are involved in long-distance Na+ transport between roots and shoots and play important roles in Na+ loading and unloading in xylem and phloem, respectively, thus affecting plant salt tolerance. In addition, SOS1,an Na+/H+ antiporter located in the plasma membrane, together with protein kinase SOS2 and Ca2+ binding protein SOS3, forms a complex of SOS, which plays a critical role in Na+ homeostasis in cells. This regulatory mechanism is conserved among dicots and monocots both in structure and function. The SOS complex, together with other Na+/H+ antiporters and H+ pumps localizing in plasma membrane or tonoplast, controls cellular Na+ homeostasis.