Under heavy metal stress,higher plants initiate a set of defense responses,among which biosynthesis of phytochelatins (PCs) is important. PCs are rich in cystein and biosynthesized by phytochelatin synthase. The chemical structure of PCs and their ability to form complexes with a large range of metal ions is clear. Up to now,these peptides are known to play an important role in both endogenous metal ion homeostasis and heavy metal ion detoxification. The mechanism of cadmium tolerance is illustrated in detail. A model of this mechanism suggested that the detoxification process of cadmium include such steps as PCs induction,transport of cadmium into the tonoplast,formation of the HMW-Cd-PCs complexes and sequestration in vacuole. At the same time,PCs also have other functions,such as detoxification of arsenic,protecting enzyme from metal ion inhibition and supplying metal ion as a cofactor to the enzyme potentially. However,a lot of questions about its biological function remain to be answered. In 1999,three independent labs isolated the genes encoding the PCs synthase. This breakthrough of plant heavy metal tolerance research gave us a chance to further study the heavy metal tolerance mechanism. All the results from the reserch of PCs have a great application potential in phytoremidation. Fig 1,Ref
