Effects of exogenous spermine on chlorophyll fluorescence, antioxidant system and ultrastructure of chloroplasts in Cucumis sativus L. under salt stress

► Salinity cause the overproduction of ROS in chloroplasts of cucumber seedlings. ► Salinity-induced oxidative damage to the structure of photosynthetic apparatus. ► Spm increased the photochemical efficiency of salt-stressed cucumber leaves. ► Spm regulated antioxidant systems in chloroplast of the salt-stressed plants.