Effect of Sodium Metasilicate on Reduction of Oxidative Damages in Lettuce (Lactuca sativa cv. ‘siahoo’) under Manganese Toxicity Stress

Manganese is a microelement for plants and is not actually counted as a metal pollutant. Manganese toxicity in some agricultural soils due to its excessive regeneration leads to undesirable symptoms in plants. Silicon is well known as reducing stress and toxic effects of some elements. A hydroponic experiment was conducted to evaluate the effect of silicon and manganese on leave of lettuce (Lactuca sativa L. cv. Siahoo) in greenhouse of Agricultural Faculty of Maragheh, Iran in 2016. The experimental design was completely randomized factorial design with three replicates. The treatments were three level of manganese (0.5, 2.5 and 5 mg/l) from MnSO4 source and three level of silicon (0, 14 and 28 mg.L-1) from Sodium metasilicate source. The results showed that with increasing manganese concentration, the levels of malondialdehyde, catalase, ascorbate peroxidase and hydrogen peroxide increased and total protein and fresh weight and dry weight of plant decreased. The highest plant fresh and dry weight loss was observed in 5 mg.L-1 manganese. Sodium metasilicate significantly reduced the level of malondialdehyde and hydrogen peroxide and increased the activity of the enzyme catalase, ascorbate peroxidase, total protein, plant fresh and dry weight. In general, application of high concentrations of manganese in nutrient solution decreases the plant growth and yield, while silicon application reduce the toxic effects of manganese and enhances the plant yield.