Cadmium sequestration in Chlamydomonas reinhardtii

We demonstrated that phytochelatin (PC) is the major intracellular cadmium (Cd) chelator in the microalga, Chlamydomonas reinharcitii. From Cd challenged algal cells, two types of PC-Cd complexes were purified and characterized; the high molecular weight (HMW) complex and the lower molecular weight (LMW) complex. These complexes differed in accumulation kinetics, PC profile, acid labile sulfide content. in vivo turnover rate, UV absorption spectra, and acid sensitivity in vitro. Although the HMW complex appeared first during Cd treatment, our detailed analysis suggested the quick conversion of LMW complex to HMW complex inside the algal cells and HMW complex contributed to stable Cd sequestration. The accumulation of LMW complex appeared to be an early sign of metal stress. In several Cd resistant mutants generated in this lab, the level of PC production was proportional to the capacity of Cd accumulation. Cd-resistant mutant could grow in elevated Cd concentration through different mechanisms. One type of mutant produced high levels of HMW complex with a distinct PC profile to facilitate Cd accumulation. In this mutant, we detected higher content of reduced glutathione and cystein than the wild type. This study suggested the involvement of assimilatory sulfate reduction pathway(s) in Cd sequestration. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved