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. Furthermore, Chuanxiong roots achieved growth-stress resistance balance (exhibiting hormesis) via the carbon metabolism pathway (the material and energy basis), the sulfur metabolism (the core detoxification pathway), and the phenylpropanoid biosynthesis (structural and chemical defense). This study provides a theoretical basis for developing precise regulatory techniques to reduce heavy metals (HMs) accumulation in medicinal plants, and thus safeguard their quality and safety.