The effects of silicon nutrition on salinity-induced and cadmium toxicity oxidative damages and antioxidative response of cucumber was investigated in a greenhouse experiment. Two cucumber cultivars ( Cucumis sativus L. cvs. Negin and Super Dominus) were exposed to two levels of salinity (0 and 50 mM NaCl) and two levels of cadmium (0 and 5 µm CdCl 2 ) and were supplied or non-supplied with Si. Salinity and cadmium stress resulted in significant shoot growth reduction of both cucumber cultivars although the magnitude of this decrease was greater for ‘Super Dominus’. Silicon nutrition had stimulating effect on shoot growth of both cultivars particularly under salt stress conditions. The effect of salinity and cadmium stress on the leaf MDA content was dependent on the cucumber cultivar. Salinity and cadmium stress increased leaf MDA content in ‘Super Duminus’ while had no effect on the MDA content in ‘Negin’. Shoot MDA contents in the leaves of cucumber plants grown at the 50 mM NaCl treatment was reduced by Si nutrition. Salinity increased while Si decreased K/Na ratio in the shoots of cucumber plants. The effect of salinity on leaf activity of CAT and APX was dependent on the enzyme type and plant cultivar. Activity of GPX in the leaves of both cucumber cultivars was similarly affected by salinity. On the other hand, Si nutrition significantly reduced shoot concentrations of MDA. The K/Na ratio and Ca concentration was greater in the leaves of cucumber plants supplemented with Si than those did not supplement with Si. Activity of CAT, APX, and GPX in the leaves of both cucumber cultivars was increased in the presence of Si although this increase was cultivar-dependent. According to the results, Si could alleviate impaired root integrity of cucumber plants exposed to salinity and cadmium stress via increasing activity of antioxidant enzymes. Higher activity of CAT, APX, and GPX in ‘Negin’ compared with ‘Super Dominus’ might be associated with greater tolerance of ‘Negin’ to salinity. Keywords: Environmental stre Cucumis sativus L.; Beneficial elements; oxidative stre CAT; APX; GPX.
