Abstract: The biosynthesis pathway of phytochelatins (PC) and its function in heavy metal tolerance of higher plants were summarized in this paper. The toxic heavy metal accumulation in soil would deteriorates crop growth and yield components, and threaten the agro-products security. There were significantly differences in the accumulation and tolerance to heavy metals among plant species and genotypes. The formation of PCin response to the stress caused by heavy metals was one of the truly adaptive responses occurred commonly in higher plants. In the heavy metal tolerant genotypes, there was a much higher accumulation of PCthan the non-tolerant lines. Glutathione (GSH) was the substrate for the synthesis of PC, which chelated the metals. The inactive toxic metal ions of metal-PC chelatins were subsequently transported from cytosol to vacuole before they could poison the enzymes of life-supporting metabolic routes, and transiently stored in vacuole to reduce the heavy metal concentration in cytosol, thus, heavy metal detoxification was attained. The break through of genetic mechanism and bio-chemical pathway of PC synthesis induced by heavy metals would depend on the further study on molecular biology in this field. The isolation of Cd-sensitive cad1 and cad2 mutants of Arabidopsis thaliana, that was deficient in PC, demonstrted the importance of PCfor heavy metal tolerance. The effect of PC on food security and on phytoremediation of soil and water contaminated by heavy metals was also discussed in this paper.

Key words: Heavy metal, Phytochelatin, Molecular biology, Tolerance, spatial resolution, multispectral remote sensing, scale effect., tree species classification, texture information