Centro de Estudios Fotosintéticos y Bioquímicos, CONICET, Suipacha 531, 2000 Rosario, Argentina.
J Inorg Biochem. 2012 Dec;117:306-15. doi: 10.1016/j.jinorgbio.2012.08.020. Epub 2012 Sep 7.
Cadmium is a highly toxic heavy metal for both plants and animals. The presence of Cd in agricultural soils is of major concern regarding its entry into the food chain, since Cd compounds are readily taken up by plants, and accumulated in edible parts due to their high solubility. In this study, we first demonstrate the high capacity for Cd concentration of soybean grains. Consequently, we considered the study and characterization of the molecular determinants of Cd accumulation -such as metallothioneins (MT)- to be of major practical importance. We report here the first characterization of the soybean MT system, with the identification of nine genes (one of which is a truncated pseudogene), belonging to the four plant MT types. The most highly expressed of each type was chosen for further function analysis. All of them are expressed at high levels in soybean tissues: GmMT1, GmMT2 and GmMT3 in roots, shoots and seeds, and GmMT4 only in seeds. The corresponding recombinant soybean MTs, synthesized in Escherichia coli cells cultured in metal supplemented media, exhibit greater cadmium than zinc binding capacity. These results suggest a definite role of GmMTs in Cd(II) accumulation as one of the main responses of soybean to an overload of this metal.
镉是一种对植物和动物都有高度毒性的重金属。农业土壤中存在的镉引起了人们的极大关注，因为镉化合物很容易被植物吸收，并由于其高溶解度而在可食用部分积累，从而进入食物链。在本研究中，我们首先证明了大豆籽粒对镉的高浓缩能力。因此，我们认为研究和表征镉积累的分子决定因素（如金属硫蛋白（MT））具有重要的实际意义。我们在这里报告了大豆 MT 系统的首次特征描述，鉴定了九个基因（其中一个是截短的假基因），属于四种植物 MT 类型。每种类型中表达量最高的基因被选择进行进一步的功能分析。它们在大豆组织中均高水平表达：根、茎和种子中的 GmMT1、GmMT2 和 GmMT3，以及仅在种子中的 GmMT4。在金属补充培养基中培养的大肠杆菌细胞中合成的相应重组大豆 MT 表现出比锌更高的镉结合能力。这些结果表明 GmMTs 在 Cd(II)积累中发挥了明确的作用，是大豆对这种金属超负荷的主要反应之一。
