Molecular and Physiological Insights into CAT- and SOD-Associated Redox Homeostasis Under Salt Stress in Artemisia argyi.

Soil salinity disrupts redox homeostasis and limits plant growth and development. Although catalase (CAT) and superoxide dismutase (SOD) are key enzymatic antioxidants, the CAT and SOD gene families have not been characterized in Artemisia argyi (A. argyi), a species of medicinal and ecological importance. While SOD and CAT serve as the primary enzymatic scavengers for reactive oxygen species (ROS) detoxification, their genomic architecture and stress-responsive regulatory networks in A. argyi have remained uncharacterized. In this study, we conducted the first comprehensive genome-wide analysis of these gene families in A. argyi, identifying 22 structurally conserved members (8 AarCATs and 14 AarSODs). Collinearity and synteny analyses revealed strict lineage-specific evolutionary conservation, while tertiary protein modeling and subcellular localization illustrated a highly organized multi-organelle defense compartmentalization. High salinity (up to 200 mM NaCl) reduced the stomatal conductance and net photosynthetic rate. Salt stress reduced growth and increased osmoprotectant and antioxidant accumulation in A. argyi. Furthermore, histochemical staining using nitroblue tetrazolium (NBT) and 3,3'-Diaminobenzidine (DAB) provided comprehensive evidence of significant accumulation of ROS in leaves, which indicates the intense oxidative stress triggered by ionic stress. Tissue-specific analysis revealed that AarCAT1, AarCSD1, and AarFSD2 were 3.9-, 7.9-, and 12.7-fold higher in leaves than in roots, respectively. Under stress, AarCAT6 and AarCSD1 were strongly repressed in leaves by ~50% and ~46-70%, respectively, whereas AarMSD2 and AarMSD3 were significantly induced in roots by ~2.2- and ~1.8-fold. These distinct expression patterns suggest their potential involvement in tissue-specific stress adaptation and ROS homeostasis. These findings uncover the evolutionary and physiological basis of salt tolerance in A. argyi, providing genetic targets for climate-resilient breeding.