Abstract: This paper studied the effects of different concentration exogenous spermine (Spm) on the activities of antioxidant enzymes (SOD, CAT, POD, APX), generation rate of O^-·₂, and contents of MDA, free polyamines (PAs), chlorophyll and soluble protein inNymphoides peltatum leaves under 15 μmol·L^-1 Hg stress. The results showed that under the Hg stress, 0.05-0.5 mmol·L^-1 of exogenous Spm could significantly increase the contents of leaf spermidine (Spd), Spm, chlorophyll, and soluble protein, promote the activities of SOD, CAT, and APX, and decrease the generation rate of O^-·₂ and the accumulation of MDA. It was suggested that 0.05-0.5 mmol·L^-1 of exogenous Spm could enhance the resistance of N. peltatum to oxidant stress, and mitigate the toxic effects of Hg. The optimum dose of exogenous Spm was 0.05-0.1 mmol·L^-1, while 5 mmol·L^-1 of Spm could aggravate the toxic effects of Hg.

Key words: CO₂, Greenhouse, Lily, Allelochemical