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The protective role of spermidine addition in media to Salix matsudana exposed to Pb was investigated by a hydroponic experiment in this study. The application of spermidine enhanced the biomass of S. matsudana exposed to Pb. Pb induced an increase in Pb levels in all organs of S. matsudana with the order of roots (maximum of 27616.0 mg/kg DW) > cuttings > twigs > leaves. Exogenous spermidine promoted the accumulation of Pb in the roots, but inhibited the Pb translocation to the shoots and thus the Pb content in the twigs and leaves. The Pb-induced decrease in the concentrations of spermidine, soluble protein, and nitric oxide was elevated by the application of spermidine in the leaves of S. matsudana . Exogenous spermidine could also effectively up-regulate the antioxidative capacity and reduced the accumulation of superoxide anion, hydrogen peroxide, malondialdehyde, and putrescine. The results suggested that S. matsudana could accumulate a high level of Pb in the roots, and exogenous spermidine could enhance S. matsudana tolerance to Pb by the synergistic promotion of Pb accumulation in the roots and the levels of spermidine, nitric oxide, and antioxidants in the leaves. [ABSTRACT FROM AUTHOR]