Application of selenium in lowering damage of cadmium, nickel and lead stresses on germination and antioxidant activity of cucumber seedlings (Cucumis sativus L.)

Selenium (Se) is a beneficial element with anti-oxidant and anti-viral properties that strengthens the defense system and increases plant adaptability under environmental stress conditions. In present study we examined the effect of Se on alleviating adverse effect of Cd, Pb and Ni alone and in combination together in cucumber (Cucumis sativus cv. Super Dominus). The research was conducted using a completely randomized design with factorial arrangement in three replications for two germination tests. The first experiment was carried out to determine the optimal effectiveness of Se and heavy metal toxicity threshold levels, which contain levels of Se (0, 4, 6, 8, 10 mg.L -1 ), cadmium (0, 10, 15, 20, 25 µM), nickel (0, 50, 100, 150, 200 µM) e and lead (0, 20, 40, 60, 100 µM). The second experiment were consisted of two levels of Se (0 and 8 mgL-1) and toxicity threshold levels of heavy metals, including cadmium (0, 25 µM), nickel (0, 200 µM) and lead (0, 100 µM) treatments. The result showed that the germination percentage and germination rate significantly reduced at all heavy metal stress and Se has beneficial effect in alleviation of toxicity of heavy metal. Heavy metals stress increased electron leakage (EL) malondialdehyde (MDA) and Se supplementation enhance EL and MDA under heavy metal stress. Cd, Pb and Ni alone or in combination together significantly reduced enzyme activity such as catalase (CAT), glutathione peroxidase (GPX) and ascorbate peroxidases (APX) in cucumber leaves and Se increased enzyme activity in stress condition in comparison with non-Se application. In general, Se has beneficial effect in alleviation of heavy metals stress in cucumber during germination by preventing oxidative damages.