Exogenous spermidine enhances Hydrocharis dubia cadmium tolerance

The effects of exogenous spermidine (Spd) on arginine decarboxylase (ADC), ornithine decarboxylase (ODC), polyamine oxidase (PAO), and diamine oxidase (DAO) activities, the rate of superoxide radical (O (2) (center dot-) ) generation and polyamine (PA), malondialdehyde (MDA), and H2O2 contents in Hydrocharis dubia (Bl.) Backer leaves under cadmium (Cd) toxicity were studied after 6-day treatment. Cd stress increased putrescine (Put) level and lowered spermidine (Spd) and spermine (Spm) levels. In addition, the activities of ADC, DAO, and PAO were increased, while that of ODC was decreased. Exogenous application of Spd markedly reversed these Cd-induced effects. It also significantly reduced the generation of O (2) (center dot-) and H2O2 and prevented lipid peroxidation. These results suggest that exogenous Spd can enhance the tolerance of H. dubia to Cd. The maintenance of PA homeostasis was necessary for plant metal tolerance.