ABSTRACT
Effects of different exogenous spermidine concentrations on the activities of some enzymes (SOD, CAT, POD, APX), O(-)(2) generation rate, the MDA, chlorophyll, soluble protein and polyamine contents in leaves of Nymphoides peltatum without Hg(2+) stress or under Hg(2+) stress were studied. The results showed that: (1) The spermidine (Spd) and spermine (Spm) content dropped significantly under Hg(2+) (3 mg/L) stress 4 d, while that of putrescine (Put) was increased markedly. Exogenous Spd could increase the Spd and Spm content in leaves, while that of Put lowered at first and rose later. (2) Hg(2+) 3 mg/L decreased drastically the activities of SOD, CAT and APX, increased the O(-)(2) generation rate, led to the accumulation of a large amount of MDA and loss of chlorophyll and soluble protein. Exogenous Spd could enhance the activities of SOD, CAT and APX, decrease O(-)(2) generation rate and reduce the MDA content. In addition, Spd could also decrease the loss of chlorophyll and soluble protein content induced by Hg(2+) stress, enhance the ability of Nymphoides peltatum to resist Hg(2+) stress. The most suitable concentration of Spd was in the range 0.1-0.5 mmol/L.
