Involvement of polyamines in adaptation of Potamogeton crispus L. to cadmium stress

The effects of increasing concentrations of cadmium (Cd) on the ultrastructure, Cd accumulation, generation of O-2(center dot-), contents of ascorbate (AsA), reduced glutathione (GSH) and polyamines (PAs), as well as the activities of polyamine oxidase (PAO) (EC 1.5.3.3) and diamine oxidase (DAO) (EC 1.4.3.6) were investigated in the leaves of Potamogeton crispus. Cd exposure resulted in significant damage in chloroplasts and mitochondria, suggesting that Cd hastened the senescence of the tested plants. The accumulation of Cd was found to increase in a concentration-dependent manner, accompanied by increased production of O-2(center dot-). AsA content increased progressively up to 70 mu M Cd, followed by a decline at higher concentration. GSH content slightly increased up to 70 mu M Cd and then declined. In addition, Cd treatment increased the putrescine (Put) content, while decreasing spermidine (Spd) and spermine (Spm) contents, which reduced the ratio of free (Spd + Spm)/Put in the leaves. PS-conjugated PAs changed in the same pattern as free PAs, while PIS-bound PAs was different. PIS-bound Put content enhanced with the increase of Cd concentration up to 50 mu M and then decreased, and PIS-bound Spd and Spm contents decreased to a lesser extent. Moreover, the activities of PAO and DAO increased significantly with the increase of the Cd concentrations, reaching the peak values at 70 mu M Cd. Our results suggested that certain PAs and PAs forms could play a significant role in the adaptation mechanism of P. crispus under Cd stress. (C) 2010 Elsevier B.V. All rights reserved.