重金属污染是全球面临的亟待解决的生态问题。利用植物对重金属的富集作用来清除环境重金属污染即植物修复已成为重要的环境生物技术之一。这一技术的长远发展有赖于在重金属富集或耐受中起关键作用的基因的克隆和应用。植物络合素是植物体内一类重要的对重金属起螯合作用的多肽, 其合成受植物络合素合酶的催化。该文取得了如下研究结果：1）通过原子吸收测定表明，在大蒜(Allium sativum)的根部可以积累3 000 mg·kg－１的重金属镉；2)将克隆的大蒜植物络合素合酶基因(AsPCS)置于酵母表达启动子之下，构建酵母表达载体，并将其分别转入了因CUP1和acr3基因缺失而对重金属镉和砷敏感的酵母突变体菌株后，发现来自大蒜的AsPCS基因的表达使酵母CUP1缺失菌株对镉的耐受性提高了4倍, acr3缺失菌株对砷的耐受性提高了两倍；3）表达AsPCS基因酵母的生长模式证实了AsPCS基因的表达是酵母对重金属耐受性提高的原因。这些结果暗示, 大蒜植物络合素合酶基因在大蒜对重金属的抗性及大蒜根部对镉的积累中起关键作用,可作为重要的基因元件应用到修复污染的植物基因工程中。
Remediation of soils contaminated by heavy metals is one of the most pressing environmental problems facing the biosphere. Phytoremediation is a new biotechnique to clean environmental pollutants by plants, including heavy metals. In the long term, major improvements in phytoremediation will rely on the isolation and application of the genes from various plant, bacteria, and animal sources that can enhance metal accumulation. Phytochelatin is a type of polypeptide that combines heavy metals in plants, and its synthesis is regulated by phytochelatin synthesase (PC synthase). In this study, we determined that the roots of garlic (Allium sativum) can accumulate up to 3 000 mg·kg－１ cadmium. A yeast-expressed plasmid with PC synthesase from garlic (AsPCS) was constructed and transferred into heavy metal sensitive yeast mutant cells. The results showed that the expression of AsPCS was improved by 4 folds in yeast cells with cadmium tolerance and a 2 folds increase was observed in arsenate tolerant cells as compared to the control cells. Further study about the growth patterns of AsPCS-expressed yeast indicated that the expression of AsPCS was critical for yeast heavy metal tolerance. As an important role in the garlic‘s response to heavy metal, AsPCS can work as a significant gene tool in the phytoremediation of heavy metal pollution.