Phytochelatins in Cadmium-treated Seedlings of Canavalia lineata

Nonprotein thiol production in Canavalia lineata was stimulated most effectively by Cd. The levels of total nonprotein thiol of leaves and roots were increased even at 1 μM Cd. At 50 μM Cd, total nonprotein thiol contents increased continuously during 5 days up to 4fold in leaves and 18-fold of the control in roots nonprotein thiol content declined at 100 μM Cd. Glutathione declined very rapidly in leaves and roots exposed to Cd. On the other hand, cysteine and γ-glutamylcysteine increased after Cd exposure in roots as well as in leaves, and the increase of both thiols was proportional to Cd concentration. At 50 μM Cd, the activities of γ-glutamylcysteine synthetase and glutathione synthetase increased significantly. The phytochelatin-Cd complexes of leaves and roots exposed to 50 μM Cd for 5 days were separated by Sephadex G-50 column chromatography. The molecular weights of the complexes were 8.7 kDa and 13.8 kDa and the SH:Cd ratios were 2:1 and 1:1 in leaves and roots, respectively. It is noteworthy that different ratios of phytochelatin-Cd complexes could be formed within a species.