Effects of Exogenous Spermidine on Antioxidant System Responses of Typha latifolia L. Under Cd2+ Stress

The effects of foliar spraying with spermidine (Spd), ranging in concentration from 0.25 to 0.50mmol/L, on the antioxidant system under Cd2 stress (range 0.1- 0.2 mmol/L Cd2 ) in Typha latifolia L.grown hydroponically were investigated in order to offer a referenced evidence for an understanding of the mechanism by which polyamines (PAs) relieve the damage to plants by heavy metal and improve the phytoremediation efficiency of heavy metal-contaminated water. The results showed that Cd2 stress inhydrogen peroxide (H2O2) and malondialdehyde (MDA) contents in both leaves and caudices. With theexception of superoxide dismutase (SOD) activity in the leaves, an increase in the activities of catalase (CAT), guaiacol peroxidase (GPX), and glutathione reductase (GR) was observed in both leaves and caudices,SOD activity was increased in caudices, and ascorbate peroxidase (APX) activity was increased in leaves following Cd2 treatment. The reduced glutathione (GSH) content in both leaves and caudices and the reductive ascorbate content in leaves was obviously increased, which were prompted by the application of exogenous Spd. Spraying with Spd increased the activity of GR and APX in both leaves and caudices,whereas the activity of SOD, CAT, and GPX was increased only in caudices following spraying with Spd.with Spd. The decrease in MDA was more obvious following the application of 0.25 than 0.50 mmol/L Spd.It is supposed that exogenous Spd elevated the tolerance of T. latifolia under Cd2 stress primarily by increasing GR activity and the GSH level.