Metallothioneins
Unlike phytochelatins, metallothioneins
(MTs) are found in animals as well as plants. They are gene-encoded polypeptides
(8-14kDa) (Robinson, et al. 1993) thought to be aggregates of phytochelatins
(Prasad, 1995). MTs behave similarly to PCs, and often metal complexation
duties are shared between MTs and PCs as seen in Datura and Zea maize (Rivai,
et al. 1990). MT have highest complexing affinity for Cu, and are
induced by exposure to it (Murphy, et al. 1997).
Introduction of mammalian
MT into B. campestris, B. nappus and N. tabacum has conferred
Cd tolerance by increasing complexation and minimizing translocation of
Cd to the shoots (Maiti, et al. 1989.). In the plant kingdom, MT-like proteins
have been found in tomato (Bartolf, et al. 1980) pea, soybean (Casterline
and Barnett, 1982) and maize.
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