報告書番号

U02001

タイトル（和文）

植物による環境修復(2) -－遺伝子組換えタバコにおけるカドミウム蓄積量の増加－-

タイトル（英文）

Utilization of the apoplasmic space in tobacco for accumulation of cadmium

概要 （図表や脚注は「報告書全文」に掲載しております）

アポプラズマ領域は細胞膜と細胞壁の間に存在する、植物細胞に特有の空隙である。本実験ではこの領域への輸送に関与することが明らかにされているタバコインベルテースのトランジットペプチド（TP）部分の遺伝子配列を用いて、フェリチン、あるいはメタロチオネインをタバコのアポプラズマ領域に輸送した。その結果、アポプラズマにおけるフェリチンの発現により、地上部組織において非形質転換タバコの２倍強の鉄含有量を示すとともに、わずかながら高濃度の鉄（0.5mM）に対する耐性を示した。また、アポプラズマ領域におけるメタロチオネインの発現により、最大で非形質転換タバコの約２．５倍のカドミウム含有量を示すタバコの作出に成功した（培地のカドミウム濃度が10マイクロモルのとき、根部における値）。また、メタロチオネインを発現するタバコは、非形質転換タバコに比べ培地のカドミウム濃度が50マイクロモル以下のとき、生育量が大きかった。

概要 （英文）

Heavy metals are the harmful elements, which injure human at most frequent occasion. We can see many destructive damages by the heavy metal pollutions from mines or factories from ancient eras. However, it is not a past problem but is still a present one at such industrial sites. Rather, it is a new problem at the urban sites like sewage wastes landfill and heavy traffic roadside. On the other hand, a concept, called phytoremediation, is one of the solution to reduce the effects without additional energy and large costs. Many type of plants are identified as a hyper-accumulator to isolate heavy metals from soil, however, the ability is not enough. To breed new hyper-accumulator, genetically manipulation technique is helpful. Two strategies can be recognized for accumulation of metals in living plant cells; firstly, to directly increase the intake flow of the metal; and secondly, to increase the storage capacity of the metal. The first strategy is a way to increase the number of "tap" or to enlarge the diameter of "tap" as it were, which accelerates the stream of water into a prevalent "vessel". The second way is based on a hypothesis that the establishment of a new "vessel" stimulates the metabolism related to the metal intake within homeostatic mechanisms, and increases the potential for the metal accumulation in the "vessel". Our group recently demonstrated the effect of the second strategy on fortifying the iron content in crops by over-expressing a gene of the iron storage protein, "ferritin". However, these strategies may not work well to accumulate non-essential metals, because there are no "tap" to specifically uptake such metals into cell. A few molecule like metallothionein and phytochelatin just plays as a quencher of the harmful effect of metals but does not play a role as the "tap" or the "vessel" even in the case of over-expression. So, we tried to make a new system using apoplasmic space as the third way to accumulate metals in plant. That is, a metal-binding molecule in the apoplasmic space may trap metals without the specific "tap" and may supply an enough space to trap metals before it coming into cell. We used alpha domain of human metallothionein as the metal-binding molecule, which is expressed with the transit peptide of tobacco invertase-inhibitor to be in the apoplasmic space under the regulation of CaMV 35S promoter in tobacco. The T1 tobacco accumulated up to 2.5-times more cadmium than the non-transformant in the cadmium containing growing media.

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