| Synthesis of metal-binding molecules is one of the major mechanisms in metal detoxification in organisms. Phytochelatin (PC), (gamma-glu-cys) n-gly, has been demonstrated to be the major intracellular Cd chelator in both fresh water microalga C. reinhardtii and marine macroalga K. alvarezii. This study offered the first demonstration that algal species could produce two types of PC-Cd-complexes. The higher molecular weight (HMW) complex contained significantly higher level of acid-labile-sulfide than the lower molecular weight (LMW) complex. Genetic evidence has demonstrated that the increased Cd-tolerance in C. reinhardtii is correlated with the enhanced production of HMW complex. With regard to the plant growth-limiting elements of sulfur and nitrogen, as well as the energy required for their assimilation, the combination of inorganic sulfide with PC complex is advantageous in Cd sequestration. In C. reinhardtii, the sequential appearance, different turnover rate and the changing PC profile of HMW and LMW complexes were detected. The results support the transformation from LMW to HMW complex in C. reinhardtii. This study also demonstrated the correlation between the cellular glutathione (GSH) level and the length distribution of PC in C. reinhardtii. As the precursor of PC, GSH might be the limiting factor in Cd resistance. |
