CHARACTERIZATION OF CADMIUM-BINDING PEPTIDES FROM PEPPER (CAPSICUM-ANNUUM)

Pepper plants (Cupsicum annuum), like many other plant species, respon d when stressed with cadmium chloride by the synthesis of phytochelati ns [(gamma Glu-Cys)(n)Gly] (PCs) and desglycyl phytochelatins [(gamma Glu-Cys)(n)], where it = 2-4. Higher molecular weight PCs with a chain length longer than four have also been detected; their synthesis is d ependent upon the duration of the experiments and the concentrations o f Cd used in the culture medium. The synthesis of PCs and related pept ides in Cd-stressed pepper plants is also strongly suggested by the us e of buthionine sulfoximine a specific inhibitor of the gamma-glutamyl -cysteine synthetase (enzyme involved in the synthesis of glutathione, the precursor of PCs). Indeed no thiol-containing compounds were dete cted in crude extracts of Cd-treated pepper plants, when they were gro wn 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. (C) 1998 Elsevier Science Ireland Lt d. All rights reserved.