Electrochemical monitoring of phytochelatin accumulation in Nicotiana tabacum cells exposed to sub-cytotoxic and cytotoxic levels of cadmium

Cadmium belongs to the most dangerous environmental pollutants among the toxic heavy metals seriously affecting vital functions in both animal and plant cells. It has been previously shown that cadmium ions at 50-100 mu M concentrations caused tobacco BY-2 (TBY-2) cells to enter apoptosis within several days of exposure. Phytochelatins (PCs), the "plant metallothioneins", are cysteine-rich peptides involved in detoxification of heavy metals in plants. The PCs are synthesized in response to the heavy metal exposure. In this paper, we utilized electrochemical analysis to monitor accumulation of PCs in the TBY-2 cells exposed to cadmium ions. Measurements of a characteristic PC signal at mercury electrode in the presence of cobalt ions made it possible to detect changes in the cellular PC levels during the time of cultivation, starting from 30 min after exposure. Upon TBY-2 cultivation in the presence of cytotoxic cadmium concentrations, the PC levels remarkably increased during the pre-apoptotic phase and reached a limiting value at cultivation times coinciding with apoptosis trigger. The PC level observed for a sub-cytotoxic cadmium concentration (10 mu M) was about three-times lower than that observed for the 50 or 100 mu M cadmium ions after 5 days of exposure. We show that using a simple electrochemical analysis, synthesis of PCs in plant cells can be easily followed in parallel with other tests of the cellular response to the toxic heavy metal stress. (c) 2005 Elsevier B.V. All rights reserved.