Characterization of cadmium binding peptides from pepper (Capsicum annuum)

Pepper plants (Capsicum annuum), like many other plant species, respond when stressed with cadmium chloride by the synthesis of phytochelatins [(γGlu-Cys)(n)Gly] (PCs)and desglycyl phytochelatins [(γGlu-Cys)(n)], where n = 2-4. Higher molecular weight PCs with a chain length longer than four have also been detected; their synthesis is dependent upon the duration of the experiments and the concentrations of Cd used in the culture medium. The synthesis of PCs and related peptides in Cd-stressed pepper plants is also strongly suggested by the use of buthionine sulfoximine a specific inhibitor of the γ-glutamyl-cysteine synthetase (enzyme involved in the synthesis of glutathione, the precursor of PCs). Indeed no thiol-containing compounds were detected in crude extracts of Cd-treated pepper plants, when they were grown in the presence of BSO. In addition to the synthesis of PCs and PC derivatives, Cd treatment of pepper plants also leads to the synthesis of two 10-kDa proteins, which differ in their amino acid composition and are absent in untreated plants. The function and role of these two proteins is still unknown, but they might also be involved in defense mechanisms against heavy metals.