Abstract: The effect of exogenous putrescine（8 mmol · L-1）on characteristics of PSⅡ photochemistry and ion distribution were investigated in cucumber （Cucumis sativus L.）‘Jingyou 4’seedlings subjected to salt stress（75 mmol · L-1 NaCl）. Chlorophyll a fluorescence parameters showed that exogenous putrescine increased the maximum quantum efficiency（Fv/Fm），actual efficiency of PSⅡ（ФPSⅡ）and regulated thermal energy dissipation（ΦNPQ）under salt stress, and significantly increased the maximum electron transport rate of PSⅡ and the light saturation coefficient（Ek），decreased photo damage（ΦNO） in the salt-stressed plants. Salt stress resulted in a significant accumulation of Na+ and Cl- in plants, but decreased levels of K+ and Mg2+. Exogenous putrescine inhibited the transportion of Na+ and Cl- from roots to leaves, decreased the accumulation of Na+，Cl- and increased K+，Mg2+ concentration in different tissues under salt stress. The above results indicated that exogenous putrescine regulated ion distribution in salt-stressed plants, especially，by preventing the accumulation of Na+ and Cl- in the leaves which was associated with an improvement in the actual PSⅡ efficiency.

Key words: cucumber, putrscine, salt stress, PSⅡphotochemistry, ion distribution