Analysis of ferrous ion acquisition pathways in relation to cadmium tolerance and accumulation abilities of higher plants.

比较了日本200多种被子植物对主要二价金属元素（Fe、Cu、Zn和Cd）的耐性和富集能力。然后，从具有高/低镉耐性和积累能力的典型植物中分离了一些在二价金属从土壤向根系转运中起主要作用的基因，如铁转运蛋白（IRTs），并对它们的序列进行了比较。结果表明，在分子的特定单元的氨基酸序列之间的相关性可以看出，与镉的耐受性和积累能力的母体植物物种。同时，通过对多个水稻品种的生理试验和结果的统计分析，表明根、冠、叶二价金属的转运在区分水稻对镉的积累能力方面具有重要作用。此外，利用烟草进行的分子/生理实验表明，调控缺铁应答基因（如NtIRT 1和NtFRO 2）表达的信号是远距离和局部传递的混合物，信号正调控基因的表达，每个组织都能产生信号，并根据缺铁水平定量影响信号的强度。本研究所获得的植物体内金属平衡的相关知识将为开发植物修复和/或无污染种植的专用植物提供关键。

Tolerance and accumulation abilities for major divalent metals(i.e, Fe, Cu, Zn and Cd) were compared among more than 200 species/subspecies of herbal angiosperms in Japan. Then, some genes, which play a major role to transport divalent metals from the soil to roots, such as iron transporters (IRTs), were isolated from typical plants showing higher/lower cadmium tolerance and accumulation abilities, and the sequences were compared from each others. Results demonstrated that a level of correlation could be seen between the amino acid sequences at a specific unit of the molecule and the cadmium tolerance and accumulation abilities of the mother plant species. Also, physiological experiments using many rice cultivars and the statistical analyses of the results showed that root shoot divalent metal transports could play a very important role to differentiate the accumulation ability of cadmium. Furthermore, molecular/physiological experiments using tobacco indicated that, the signal regulating expression of iron-deficiency responsive genes (e.g. NtIRT1 and NtFRO2) was a mixture of long-distance- and local transmission, the signal positively regulated the gene expressions, every tissue could generate the signal and quantitatively affect the strength dependent on their level of iron deficiency. The knowledge related to metal homeostasis in plants cleared by this study would be a key to develop special plants for phytoremediation and/or contaminant-free cropping.