Abstract: In a hydroponic experiment with the seedlings of cucumber varieties “Changchun Mici" (salt-tolerant) and “Jingchun No. 2" (salt-sensitive), this paper studied the effects of exogenous spermidine (Spd) on the O₂^-. producing rate and protective enzyme activities in roots and leaves under NaCl stress. The results showed that exogenous Spd had no significant effects on the O₂^-. producing rate and the activities of superoxide dismutase (SOD),peroxidase (POD) and catalase (CAT) in the control, but further increased the activities of SOD, POD and CAT while decreased the O₂^-. producing rate under salt stress, indicating that exogenous Spd could alleviate the salt stress damage on cucumber seedlings. Comparing with “Jingchun No. 2", the cucumber variety “Changchun Mici" was less affected by saltstress, and the alleviation effect of exogenous Spd on salt stress damage was less in “Changchun Mici" than that “in Jinchun No. 2".

Key words: East China Sea, Mesocosm, Interspecific competition