Salicylic Acid Enhances Cadmium Tolerance in Cornus alba L. Seedlings Through Leaf Transcriptional Regulation and Enhanced Root Heavy Metal Sequestration

Salicylic acid enhances cadmium tolerance in plants by modulating antioxidant defenses and promoting cadmium immobilization in cell walls. However, its potential to mitigate cadmium-induced growth inhibition and physiological disturbances in the woody species Cornus alba L. remains unexplored. Cornus alba L. seedlings were used in the pot experiment with four treatments: control (CK); 40 mg·kg−1 cadmium treatment (Cd); 100 µmol·L−1 salicylic acid treatment (SA); and both salicylic acid and cadmium treatment (SACd). The results showed that salicylic acid reduced lipid peroxidation in cell membranes by enhancing root cadmium sequestration and reconfiguring the antioxidant enzyme system, thus demonstrating a synergistic protective effect. By inhibiting cadmium transport to the shoots, it thereby mitigated the cadmium-induced inhibition of photosynthesis and reproductive development. Transcriptome analysis indicated that salicylic acid upregulates key genes in sucrose and starch metabolism pathways (e.g., TPS, GN1_2_3, otsB), leading to enhanced carbon assimilation and energy supply. Furthermore, it upregulates the key terpenoid biosynthesis genes (including HMGR and GGPS), leading to a coordinated modulation of primary and secondary metabolic flux and an increased output of the related pathways. The results reveal a potential mechanism by which salicylic acid alleviates cadmium stress in Cornus alba L., offering new insights into its role in plant heavy metal stress responses.