Silicon alleviates drought stress by up-regulating physiological and biochemical responses in two contrasting bread wheat cultivars

Abstract Drought stress (DS) substantially reduces plant growth and productivity in a rainfed cropping environment. Silicon (Si) has been recognized for its potential to alleviate the detrimental effects of various environmental stresses. However, its precise mechanisms in mitigating early growth DS and its impact on related physiological and biochemical attributes remain less understood. The present study, conducted in a glasshouse using a complete randomized design with four replications, was aimed to explore the role of pre-sowing Si treatment on two contrasting wheat cultivars (RAC875, drought-tolerant; Kukri, drought-susceptible) in mitigating the physiological and biochemical disruptions induced by early growth DS (14 days at 38 ± 3% pot field capacity). The results showed that Si treatment significantly increased the number of productive tillers and fresh weight in both cultivars under DS. Compared to the control (DS without Si treatment), Si treatment significantly enhanced chlorophyll content (RAC875, 8.7%; Kukri, 12.7%), relative water content (RAC875, 10.8%; Kukri, 18.1%), and chlorophyll fluorescence (RAC875, 10.1%; Kukri, 22.3%) under DS conditions. Additionally, Si treatment increased total soluble sugars, fructose content, and free amino acids while reducing proline content and lipid peroxidation concentrations in both cultivars under DS. Moreover, Si treatment significantly boosted cellular antioxidant activities, including ascorbate peroxidase (RAC875, 11.3%; Kukri, 9.2%), catalase (RAC875, 22.2%; Kukri, 25.5%), and peroxidase (RAC875, 19%; Kukri, 15.8%) under DS. Overall, these results show that Si effectively alleviates early growth DS by up-regulating antioxidants, osmoprotectants, and the photochemical process, thereby improving plant growth and productivity through enhanced photosynthesis.