Detoxification of arsenic by phytochelatins in plants

As is a ubiquitous element present in the atmosphere as well as in the aqua tic and terrestrial environments. Arsenite and arsenate are the major forms of As intoxication, and these anions are readily taken up by plants. Both anions efficiently induce the biosynthesis of phytochelatins (PCs) ([gamma- glutamate-cysteine](n)-glycine) in vivo and in vitro. The rapid induction o f the metal-binding PCs has been observed in cell suspension cultures of Ra uvolfia serpentina, in seedlings of Arabidopsis, and in enzyme preparations of Silene vulgaris upon challenge to arsenicals. The rate of PC formation in enzyme preparations was lower compared with Cd-induced biosynthesis, but was accompanied by a prolonged induction phase that resulted finally in hi gher peptide levels. An approximately 3:1 ratio of the sulfhydryl groups fr om PCs to As is compatible with reported As-glutathione complexes. The iden tity of the As-induced PCs and of reconstituted metal-peptide complexes has unequivocally been demonstrated by electrospray ionization mass spectrosco py. Gel filtration experiments and inhibitor studies also indicate a comple xation and detoxification of As by the induced PCs.