Silicon Supplementation Induces Physiological and Biochemical Changes That Assist Lettuce Salinity Tolerance

Little is known abou the effects of silicon on the physiological and biochemical characteristics of vegetables under salt stress. Our aim was to evaluate Silicon's role as attenuator of negative effects of saline stress in lettuce plants. The experiment was carried out in a completely randomized design with four replicates in a a 3 x 2 factorial arrangement, three salinity levels (1.65, 3.65, 7.65 dS m(-1)) with and without silicon (0 and 2 mM). Gas exchange, chlorophyll 'a' fluorescence, photosynthetic pigments, lipid peroxidation, hydrogen peroxide (H2O2) levels, enzymatic and non-enzymatic mechanisms and accumulation of inorganic ions were evaluated. Salinity increased the total chlorophyll and maintained a high Fv/Fm ratio (above 0.80). Silicon reduced gas exchange at severe salt stress. The activity of ascorbate peroxidase enzymes and guaiacol increased in high-salinity stress, which resulted in a lower content of H2O2 and lipid peroxidation. Si induced the reduction of antioxidant enzymes activity in severe stress. Na+ and Cl(-)ions increased with the saline water, while K(+)and the K+/Na(+)ratio decreased. The limited accumulation of silicon in lettuce leaf tissues has not been sufficient to induce physiological responses that lead to increased production under high-salinity conditions.