Cadmium distribution and tolerance mechanisms in Artemisia argyi under cadmium stress

The dried leaf is the medicinal organ of Artemisia argyi, but the relationships among Cd allocation, physiological defense, cellular injury, and transcriptional responses remain incompletely resolved. We evaluated these responses after 14 d of hydroponic exposure to 0–40 mg/L Cd. Growth was little affected at 1–10 mg/L but was markedly inhibited at 20–40 mg/L. POD activity and proline content increased, whereas CAT declined at high exposure and total flavonoids showed a biphasic response. Cd accumulated mainly in roots and in the operationally defined operational leaf cell-wall fraction, and the translocation factor decreased to 0.59 at 40 mg/L. Representative transmission electron micrographs showed progressive thylakoid disorganization despite relatively stable chlorophyll contents. RNA-seq of 11 libraries identified 8,434 DEGs in the control-versus-Cd40 comparison, with prominent responses in phenylpropanoid metabolism, pectin modification, transmembrane transport, photosynthesis, and flavonoid- and terpenoid-related pathways. These transcriptional patterns were directionally consistent with increased cell-wall Cd allocation, restricted high-dose translocation, chloroplast injury, and total-flavonoid changes. The results support a multi-level Cd-response model involving root retention, cell-wall sequestration, transport-related compartmentalization, and stress-responsive metabolic remodeling. The observed transition between 10 and 20 mg/L is specific to this acute hydroponic system and should not be interpreted as a field threshold. Targeted metabolite and residue analyses are required before drawing conclusions about medicinal quality or safe production.