Promoted functional enhancement of heavy metal tolerant plant and purification of heavy metal contaminated soil by it.

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We are tying to improve heavy-metal tolerance plants by introducing genes involved in heavy-metal tolerance to plants with high biomass. In this study, we overexpressed the yeast CUP1 gene to increase metallothionein synthesis in kenaf (Hibiscus cannabinus). Next, we constructed a transgenic plant that overexpressed CSase by introducing CSase gene CS3F into the kenaf, in order to confirm this correlation between CSase activity and resistance toward acidic soil. When the CSase activity of the transgenic kenaf was measured, it showed a value approximately 10 times that of the wild-type kenaf. The CSase activity of the wild-type kenaf increased 5-6 times, when sulfate ions were supplied. However, the CSase activity of the transgenic kenaf was not increased in the presence of sulfate ions. Therefore, the transgenic kenaf plant showed a CSase activity that was constantly high. The growth of the wild-type was greatly reduced in the low-pH soil (pH3.7m heavy metal rich), whereas that of the t … More ransgenic kenaf was almost the same as the growth in the control soil (pH6.1). Moreover, the chlorosis symptom was confirmed in the wild-type kenaf in the low-pH soil, but was not seen in the transgenic kenaf. the internal concentrations of heavy metals (Cu, Zn, Fe, Mn) also increased in both the wild-type and transgenic kenaf growing in the acidic soil. From this fact, we suppose that the chlorosis observed in the wild-type kenaf was due to the accumulated heavy metals and that cysteine or some derivatve of it made the excessive heavy metal harmless for some unknown reason. The influence of strengthened cystein-synthesizing ability on heavy-metal tolerance was also examined. The transgenic kenaf showed good growth compared with the wild-type kenaf when treated with 50 or 100 μM Cd. The fact that growth was not suppressed despite the high Cd concentration indicates that cysteine is able to detoxify Cd in the transgenic kenaf.In conclusion, these transgenic plants showed not only strengthened ability to synthesize cysteine but also increased tolerance toward Al, Cd, and acidic conditions. Thus, plants with increased cysteine-synthesizing ability should show resistance against various forms of stress. Less