Azuki bean cells are hypersensitive to cadmium and do not synthesize phytochelatins

Suspension-cultured cells of azuki bean (Vigna angularis) as well as the or iginal root tissues were hypersensitive to Cd (<10 mu M). Repeated subcultu rings with a sublethal level of Cd (1-10 mu M) did not affect the subsequen t response of cells to inhibitory levels of Cd (10-100 mu M). The azuki bea n cells challenged to Cd did not contain phytochelatin (PC) peptides, unlik e tomato (Lycopersicon esculentum) cells that have a substantial tolerance to Cd (>100 mu M). Both of the cell suspensions contained a similar level o f reduced glutathione (GSH) when grown in the absence of Cd. Externally app lied GSH to azuki bean cells recovered neither Cd tolerance nor PC synthesi s of the cells. Furthermore, enzyme assays in vitro revealed that the prote in extracts of azuki bean cells had no activity converting GSH to PCs, unli ke tomato. These results suggest that azuki bean cells are lacking in the P C synthase activity per se, hence being Cd hypersensitive. We concluded tha t the PC synthase has an important role in Cd tolerance of suspension-cultu red cells.