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

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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.