Application of silicon to irrigated and water deficit sorghum plants increases yield via the regulation of primary, antioxidant, and osmoregulatory metabolism

Silicon (Si) supplementation is related to the induction of different tolerance mechanisms, leading to higher farm crop yields. The objective of this study was to elucidate the Si action mechanisms as a beneficial element in primary, antioxidant, and osmoregulatory metabolism in sorghum plants cultivated in soil under two different water availability conditions. Plants of the sorghum BRS332 genotype, sensitive to drought, were cultivated in pots in greenhouse conditions until harvest. At the pre-flowering stage, the following treatments were applied: field capacity (irrigated plants), water deficit, field capacity with Si application, and water deficit with Si application. Water deficit was conducted over 12 days, after which water potential and photosynthetic rate analyses, and leaf and root harvesting for biochemical analyses were performed. After the water deficit treatment, all plants were returned to normal irrigation until harvest, when the yield components were analyzed. Si supply occurred via fertilization at a concentration of 2 mM applied to the soil in a volume of 250 mL per day over 17 days, which corresponded to a supply on the five days preceding the beginning of stress, plus a 12-day supply during the stress period. Si alleviated the water deficit in plants, resulting in higher water potential, photosynthetic rate, grain biomass, and harvest index. Si increased the antioxidant enzymatic activity, and increased non-enzymatic antioxidants such as ascorbate and osmoregulatory substances, including proline, soluble and reducing sugars, and sucrose. Plants treated with Si showed lower damage to cell membranes (lower lipid peroxidation). The beneficial effects of Si also extended to plants that were not subjected to the water deficit treatment. Si uses the peroxide pathway as a signal to regulate metabolic responses.