Molecular physiology of zinc transport in the Zn hyperaccumulator Thlaspi caerulescens
Molecular physiology of zinc transport in the Zn hyperaccumulator Thlaspi caerulescens
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DOI：
10.1093/jexbot/51.342.71
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发表时间：
2000-01-01
影响因子：
6.9
通讯作者：
Kochian, LV
中科院分区：
文献类型：
--
作者：
Lasat, MM;Pence, NS;Kochian, LV
本文综述了本实验室对超积累植物紫云英(Tlaspi Caerulescens)中重金属(Zn)运输的生理和分子方面的最新研究，旨在阐明超积累植物Tlaspi caerulescens地上部(高达3%的锌干重)积累超高水平锌的过程。没有任何相关的中毒症状。生理学研究主要集中在利用放射性示踪通量技术(65)锌在根中的运输和区划，以及与相关的非累积物T，arvense在地上部分的转移和积累上进行比较。这些研究表明，在T，caerulescens的一些部位，锌的运输被刺激，这是造成超积累特性的原因。被刺激的运输过程包括锌进入根和叶细胞，以及锌进入木质部，锌进入根的4~5倍的刺激可能是由于根细胞中锌转运蛋白的丰富。此外，隔室分析(放射性示踪剂洗出或外排技术)表明，在这种非积累植物中，锌被隔离在根细胞的液泡中，从而延缓了锌向地上部的运输。分子研究主要集中在锌运输基因的克隆和鉴定上。将酵母锌转运缺陷突变体与T，caerulescens cDNA文库进行互补，获得了编码锌转运蛋白的基因ZNT1，序列分析表明ZNT1是最近发现的一个微量营养素转运蛋白基因家族的成员，该家族包括拟南芥铁转运蛋白IRT1和ZIP锌转运蛋白。ZNT1在酵母中的表达为该转运蛋白的生理特性研究奠定了基础。ZNT1基因编码一种高亲和力的锌转运蛋白，也可以介导低亲和力的Cd转运。ZNT1及其同源物在这两个种中的Northern分析表明，ZNT1基因在根和地上部的结构性高表达导致了ZNT1基因在蓝藻中的增强转运。在T，Arvense中，ZNT1的表达水平要低得多，这种表达是由缺锌刺激的。
In this manuscript, recent research from this laboratory into physiological and molecular aspects of heavy metal (Zn) transport in the hyperaccumulating plant species, Thlaspi caerulescens is reviewed, This research is aimed at elucidating the processes that underlie the accumulation of extraordinarily high levels of Zn in the T. caerulescens shoot (up to 3% Zn dry wt.) without any associated toxicity symptom. Physiological studies focused on the use of radiotracer flux techniques ((65)Zn(2+)) to characterize zinc transport and compartmentation in the root, and translocation and accumulation in the shoot of T. caerulescens in comparison with a related non-accumulator, T, arvense. These studies indicated that Zn transport was stimulated at a number of sites in T, caerulescens, contributing to the hyperaccumulation trait. The transport processes that were stimulated included Zn influx into both root and leaf cells, and Zn loading into the xylem, The 4- to 5-fold stimulation of Zn influx into the root was hypothesized to be due to an increased abundance of Zn transporters in T, caerulescens root cells. Additionally, compartmental analysis (radiotracer wash out or efflux techniques) was used to show that Zn was sequestered in the vacuoles of T, arvense root cells which retarded Zn translocation to the shoot in this non-accumulator species, Molecular studies have focused on the cloning and characterization of Zn transport genes in T, caerulescens. Complementation of a yeast Zn transport-defective mutant with a T, caerulescens cDNA library resulted in the recovery of a cDNA, ZNT1, that encodes a Zn transporter, Sequence analysis of ZNT1 indicated it is a member of a recently discovered micronutrient transport gene family which includes the Arabidopsis Fe transporter, IRT1, and the ZIP Zn transporters. Expression of ZNT1 in yeast allowed for a physiological characterization of this transporter. It was shown to encode a high affinity Zn transporter which can also mediate low affinity Cd transport, Northern analysis of ZNT1 and its homologue in the two Thlaspi species indicated that enhanced Zn transport in T. caerulescens results from a constitutively high expression of the ZNT1 gene in roots and shoots. In T, arvense, ZNT1 is expressed at far lower levels and this expression is stimulated by imposition of Zn deficiency.