Abstract
"Thlaspi japonicum" is the first Ni-hyperaccumulator found in Japan, and its concentrations of each element change widely corresponding to its soil condition. Especially, the plant grown at ultramafic soil area showed characteristic element contents, such as high Ni (1,553 mg (kg dry wt.)^<-1>) and extremely low Ca (2,000 mg (kg dry wt.)^<-1>). The comparative analysis of T.japonicum grown in andesitic and ultramafic rock area was performed, and Ni accumulation form in this plant was also investigated by dimethylglyoxim staining. The results obtained are summarized below. 1) Ca content of T. japonicum grown in the ultramafic soil area was about a fifth of that grown in the andesitic rock area. This plant contained high Zn and Cu ; especially, the Zn content of T. japonicum grown in andesitic rock was 10 times greater than that of the common plants. 2) The Ni compound in T. japonicum was observed as rod-shaped crystal, mainly in the epidermis of the leaves and inside the stem vessels. Many rod-form crystals gathering in fan-shapes were observed around the stomata. 3) Ni compound crystals were also observed in the plant dried at room temperature, but were destructed by heating at 70-80℃. It was considered that the latter transformation was caused by the dehydration of crystal water. 4) No crystal of Ni compound was observed in the T. japonicum grown in andesitic rock area, which contained high Ca of 10,000 mg (kg dry wt.)^<-1>. 5) The nickel content of this plant was lowered to 255 mg (kg dry wt.)^<-1> with an increasing of calcium content to 10,000 mg (kg dry wt.)^<-1> after transplanting from ultramafic soil to a mixed soil of ultramafic and calcium-rich andesitic rock. Ni compound crystals in the leaves were also observed, but they decreased dramatically. 6) Some high nickel accumulating plants (100-400 mg (kg dry wt.)^<-1>) were investigated about the existence of Ni compound crystals, but no sample containing the same crystal was gained. 7) In conclusion, the main purpose of this crystallization is thought to be Ni detoxycation ; however, it was also suggested that T. japonicum may use Ni as the proxy for Ca to remove the harmful metabolites in the low-Ca ultramafic soil.
