Impact of Salicylic Acid on Reducing Drought Stress in Rice through the Modulation of Antioxidant Enzyme Activity, Stomatal Conductance and Anatomical Features

Abstract

Drought stress significantly challenges plant growth, development, and productivity. This study examined the role of salicylic acid (SA) in enhancing drought tolerance in rice (Oryza sativa L.), specifically the Giza 183 variety, under Egyptian conditions during the 2023 growing season. Salicylic acid at 0.5 and 1 mM foliar application effectively mitigated the adverse effects of extended irrigation intervals (12 days), boosting antioxidant enzyme activity, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). The highest enzyme activities were achieved with 0.5 mM SA, showing increases of 13.62% (SOD), 13.28% (CAT), and 35.98% (POD). SA treatments also significantly enhanced stomatal conductance (SC), transpiration rate (TR), and net photosynthesis (NP). The most pronounced improvements occurred with 0.5 mM SA, resulting in increases of 25.46% (SC), 8.83% (TR), and 35.20% (NP). Anatomical features were similarly improved, with thicker stem cortical fibers, wider metaxylem vessels, and larger vascular bundles observed. Additionally, 0.5 mM SA enhanced mesophyll tissue thickness and vascular bundle dimensions, offering better structural and functional support to the plants under drought stress. The study highlights that 0.5 mM SA was particularly effective in promoting resilience, as it resulted in the thickest cortical fibers, thickest mesophyll tissues, widest metaxylem vessels, and the largest vascular bundles. These findings demonstrate the significant potential of SA in alleviating the detrimental effects of extended irrigation intervals on the Giza 183 rice variety, fostering enhanced physiological, biochemical, and anatomical adaptations to drought stress under Egyptian conditions.