Exogenous Spermidine and Spermine Enhance Cadmium Tolerance of Potamogeton malaianus

In order to investigate the effects of spermidine (Spd) and spermine (Spm) on cadmium stress, the content of chlorophyll, hydrogen peroxide (H2O2), malondialdehyde (MDA), soluble protein and proline, the rate of O-2(center dot-) generation, and activities of antioxidant enzymes (superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR)) in Potamogeton malaianus Miq. were measured. Exogenous application of Spd or Spm significantly enhanced the level of proline, retarded the loss of chlorophyll, enhanced photosynthesis, decreased the rate of O-2(center dot-) generation and H2O2 content, and prevented Cd-induced lipid peroxidation. Spd and Spm also effectively maintained the balance of antioxidant enzyme activities under Cd stress; however, GR activity was found to increase only slightly in response to polyamines (PAs). The antioxidant systems, which were modified by PAs, were able to moderate the radical-scavenging system and to lessen in this way the oxidative stress. These results suggest that both Spd and Spm can enhance Cd tolerance of P. malaianus.