HSP70 level in the leaves of Phaseolus vulgaris intoxicated with cadmium.

The heavy metal cadmium has been recognized as an extreme-ly hazardous environmental contaminant that can be highlyphytotoxic. Excessive amounts of cadmium in the environmentcan affect the performance of plants at various levels of biolog-ical organization, from the cellular up to the ecosystem level.Exposure to this harmful heavy metal can cause disturbance ofseveral essential physiological processes in plants, includingphotosynthesis, respiration and transpiration (SereginandIvanov, 2001; Ciscatoet al., 2002). At the cellular lev-el, toxic effects of cadmium may result from binding of the met-al to sulfhydryl groups of proteins, leading to disruption of pro-tein structure and function (Hall, 2002). Plants have a range of potential protective mechanisms atthe cellular level that are involved in detoxification and thus indevelopment of tolerance to heavy metal-induced stress. Thecellular stress response is a general defense mechanism com-monly seen in all organisms, from bacteria to higher organisms,including plants. This response is characterized by rapid andtransient synthesis of heat shock proteins (HSPs) (Nover,1991; Sanita di Toppiand Gabbrielli, 1999). Ap-pearance of damaged proteins in the cell after cadmium treat-ment serves as a signal that triggers the activation of HSPgenes, whose products (HSPs) prevent and repair protein dam-aged (Hightoweret al., 1994). As a member of the HSPfamily, HSP70 plays an important role under stressful condi-tions, serving to minimize injury and assist in cellular recovery(Pelham, 1984). Several different HSP70 isoforms havebeen described in plants; some of them are predominantly con-stitutively expressed, while others are inducible. There are onlya few reports indicating that cadmium intox ication provoked in-duction of HSP70 in kidney bean (Leitaet al., 1991,1993).The kidney bean (