Phytochelatins occur in all the organisms tested that produce glutathione. These range from the smallest algae (Ahner and Morel 1995, Gekeler et al. 1988) through the non-vascular plants to mono- and dicotyledonous plants (Gekeler et al. 1989). Amongst 43 species in the Family Fabaceae (=Leguminosae) 7 produced only phytochelatins, 13 only homophytoche-latins and 23 made both types of yGluCys peptides (Grill et al. 1986a). The type of peptide found depended on the monothiol produced by individual species; whether only glutathione, only homoglutathione or both. The fission yeast Schizosaccharomyces pombe produces (yGluCys)„Gly and (yGluCys)n in response to Cd and Cu (Mehra and Winge 1988) yet Candida glabrata produces the peptides with Cd and class II metallothionein with Cu
(Mehra et al. 1988). Other fungi known to contain class II metallothionein, Saccharomyces cerevisiae and Neurospora crassa, are able to produce phy-tochelatins when challenged with Cd (Kneer et al. 1992). These authors list other yeasts and Basidiomycetes containing phytochelatins. The (yGluCys)nSer peptides have been found in six members of the Poaceae along with phytochelatins and (Klapheck et al. 1994). Maize is the only plant so far that has peptides accompany phytoche-
latins and (yGluCys)n (Meuwly et al. 1995), horseradish is the only plant so far that has (yGluCys)„Gln peptides accompanying phytochelatins (Kubota et al. 2000).
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