Molecular and physiological mechanisms underlying cadmium tolerance and hormesis effect in roots of Ligusticum sinense cv. Chuanxiong

Ligusticum sinense cv. Chuanxiong (Chuanxiong) is threatened by excessive cadmium (Cd), affecting its safety and quality. This study aimed to characterize Cd distribution in Chuanxiong roots (subcellular level) and clarify its key response mechanisms to Cd stress, using ICP-MS, SEM-EDS, and transcriptome analysis. The results showed that Cd was mainly enriched in root cell walls; Cd stress significantly upregulated the activities of polyphenol oxidase (PPO, +11.50%), cinnamyl alcohol dehydrogenase (CAD, +31.05%), catechol O-methyltransferase (COMT, +28.28%), and isocitrate lyase (ICL, +121.93%) compared with the control; Cd-related genes ( NRAMP5 , CAX3 , YSL7 , etc.) and key transcription factors ( BHLH162 , ERF109 , etc.) were markedly upregulated. Further, Chuanxiong roots achieved growth-stress resistance balance (exhibiting hormesis) via carbon metabolism (material/energy basis), sulfur metabolism (core detoxification pathway), and phenylpropanoid biosynthesis (structural/chemical defense). This study provides a theoretical basis for developing precise regulation techniques to reduce heavy metals (HMs) content and ensure the quality of medicinal plants. • Cd is predominantly enriched in Chuanxiong root cell walls, clarifying its key sequestration site. • Interplay of key enzymes (phenylpropanoid, glyoxylate cycle, phenol oxidation) in Chuanxiong Cd stress response. • Chuanxiong shifts from passive Cd tolerance to active defense via coordinated metabolism, explaining its hormesis effect.