Morphophysiological Reconfiguration and Antioxidant Networking Underpin Selenium-Mediated Drought Adaptation in Nicotiana tabacum

Drought stress severely limits plant growth and productivity, prompting the need for suitable mitigation strategies. This study investigates the role of selenium in improving drought tolerance in Nicotiana tabacum (tobacco) through morphophysiological adjustments and a strengthened antioxidant defense system. Therefore, a pot experiment was conducted to investigate the effects of varying levels of sodium selenite (0, 5, 10, 15, 20 mg L^-1) on morphophysiological growth, oxidative stress indicators, antioxidant enzyme activities, and quality attributes of tobacco exposed to different drought conditions, imposed by maintaining soil moisture at 80% (D₀: no stress), 50% (D₁: moderate stress), and 30% (D₂: severe stress) of field capacity. Results revealed that drought stress significantly reduced the growth of tobacco; however, the use of sodium selenite at 15 mg L^-1 showed the highest increase in agronomic traits and biomass production of tobacco plants exposed to D₀, D₁, and D₂. After the 6 days and 20 days of drought stress, the highest decrease in malondialdehyde (MDA) content was achieved at 15 mg L^-1 sodium selenite under D₀ (47.2% and 40%); however, the maximum decrease in hydrogen peroxide (H₂O₂) (44.4% and 25%) and superoxide (O₂ ^-) contents (28% and 17.5%) was recorded at 15 mg L^-1 sodium selenite under D₂. The highest increase in antioxidant enzyme activities such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) in tobacco plants was observed with sodium selenite at 15 mg L^-1 under D₀, D₁, and D₂. Electrolyte permeability in tobacco plants was also decreased by 21.5%, 29.1%, and 37.0% with 15 mg L^-1 sodium selenite under D₀, D₁, and D₂, respectively. Meanwhile, nicotine contents were increased by 4.59%, 6.91%, and 1.01% at 20 mg L^-1 sodium selenite under D₀, D₁, and D₂, respectively. Use of sodium selenite at 15 mg L^-1 showed the maximum increase in sugar contents (13.91%, 12.13%, 16.72%) and reducing sugar contents (15.03%, 15.09%, 5.46%) in tobacco plants exposed to D₀, D₁, and D₂, respectively, as compared to the control. Present findings reveal that sodium selenite at 15 mg L^-1 significantly enhances drought resilience in tobacco by modulating growth, antioxidant defense, and physiological responses.