Abstract
Drought stress is a major abiotic factor limiting plant growth, development, and agricultural productivity worldwide. This study investigates the protective role of exogenous salicylic acid (SA) in modulating antioxidant enzyme activities and photosynthetic efficiency in Arabidopsis thaliana under drought conditions. Three-week-old A. thaliana (Col-0) plants were subjected to drought stress by withholding water for 10 days, with or without a prior foliar application of 0.5 mM SA. Our results demonstrate that drought stress significantly reduced chlorophyll content, stomatal conductance (gs), and the maximum quantum yield of photosystem II (Fv/Fm). However, exogenous SA pre-treatment mitigated these adverse effects, maintaining higher photosynthetic efficiency and relative water content (RWC). Furthermore, SA application significantly enhanced the activities of key antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and peroxidase (POD), while reducing malondialdehyde (MDA) accumulation and hydrogen peroxide (H2O2) levels. Gene expression analysis confirmed the up-regulation of AtSOD, AtCAT1, and AtAPX1 transcripts in SA-treated drought-stressed plants. These findings suggest that exogenous SA alleviates drought-induced oxidative stress in A. thaliana by enhancing the enzymatic antioxidant defense system and preserving photosynthetic machinery integrity, highlighting its potential for improving crop resilience under water-limiting environments.
