Influence of silicon on sunflower cultivars under drought stress, I: Growth, antioxidant mechanisms, and lipid peroxidation

Understanding plant responses to drought stress is essential, and there is a need to know possible physiological mechanisms of damage and drought avoidance for the genetic improvement of crops. Therefore, we investigated the effects of silicon (Si) on shoot and root growth, leaf relative water content (RWC), stomatal resistance (SR), lipid peroxidation (MDA), membrane permeability (MP), proline and hydrogen peroxide (H2O2) accumulation, nonenzymatic antioxidant activity, and the activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) of 12 sunflower cultivars grown under drought conditions. Silicon applied to the soil counteracted the deleterious effects of drought in 6 of the 12 sunflower cultivars. In general, SR and H2O2, proline, and MDA content were increased in all the cultivars under drought stress. However, application of Si decreased their levels and alleviated membrane damage (MP) significantly by increasing leaf RWC. The CAT activity was significantly decreased by drought stress, but supplemental Si increased it. In general, SOD and APX activities of the cultivars were increased by drought and decreased by application of Si. The nonenzymatic antioxidant activity of the cultivars was significantly increased by Si under drought stress. Based on the present work, it can be concluded that applied Si alleviates drought stress in sunflower cultivars by preventing membrane damage, although the cultivars showed genotypic variation in response to applied Si.