植物的硫同化及其相关酶活性在镉胁迫下的调节

植物对土壤中硫的利用包括根系对硫酸盐的吸收、转运、同化、分配等过程，也是由一系列酶和蛋白质参与和调节的代谢过程。近年来的研究表明，在植物体内，硫同化与植物对镉等重金属元素的胁迫反应机制有着密切关系。镉胁迫能调节植物对硫酸盐的吸收、转运、同化，以及半胱氨酸、谷胱甘肽（glutathione，GSH）和植物螯合肽（Dhytochelatins，pc）的合成。植物在镉胁迫下通过多种调节机制，增强对硫酸盐的吸收和还原，迅速合成半胱氨酸和谷胱甘肽等代谢物，从而合成足够的PC，以满足植物生理的需要。

Plant Sulfate Assimilation and Regulation of the Activity of Related Enzymes under Cadmium Stress

The complexation and sequestration ofheavy metal ions (e.g. Cd) by the cysteine-richpolypeptides known as phytochelatins (PC) arethought to confer heavy metal hyperaccumulationand tolerance in some plant species. PC is synthe-sized enzymatically from glutathione. The tripep-tide glutathione is a product of primary sulfurmetabolism. A variety of enzymes or proteins areinvolved in sulfur assimilation including sulfatetransporters (STs), ATP sulfurylase (ATPS), APSreductase (APSR), sulfite reductase (SiR), glu-tathione synthetase (GS) and phytochelatin synthe-sis (PCS). These enzymes or proteins are upstream-regulated by Cd at either the metabolic or the ge-netic level under metal stress. Increasing evidenceshows that enhancement of sulfate uptake and re-duction occurs with the production of PC in plantsunder heavy metal stress. In this article, the keyaspects of our recent understanding of regulatorymechanisms involved in the relation between the sul-fate assimilation and phytochelatin synthesis aredescribed.