Cysteine-Mediated Root Sequestration and Metabolic Reprogramming Alleviate Cadmium Toxicity in Chinese Cabbage

Cadmium (Cd) contamination poses a serious threat to crop productivity and food safety. Although cysteine (Cys) has been implicated in Cd detoxification, its regulatory role in Chinese cabbage remains poorly understood. Here, we demonstrate that exogenous Cys alleviates Cd toxicity by enhancing root Cd retention and coordinating multiple detoxification pathways. Cys restored biomass accumulation, root elongation, and photosynthetic performance while mitigating Cd-induced oxidative damage. Root vigour increased by 44.4%, accompanied by enhanced Cd sequestration in roots and restricted translocation to shoots. Cd concentrations in xylem sap decreased by 42.0%, and shoot Cd accumulation declined by 23.1%-44.6%. Although Cys increased Cd influx and root Cd accumulation, it inhibited long-distance Cd transport by repressing BraIRT1 and BraHMA2 expression. Cys further strengthened vacuolar immobilization by up-regulating BraABCC1/2 and BraPCS1, increasing GSH and PC2-PC4 contents, and improving the GSH/GSSG ratio, thereby supporting Cd chelation and redox homoeostasis. Time-resolved transcriptomics revealed attenuation of Cd-induced sulphate assimilation hyperactivation, enhanced GSH regeneration, and a metabolic shift from lignin biosynthesis toward glycosylated phenylpropanoid detoxification products, as validated by qRT-PCR. Together, these results identify Cys as a practical strategy to reduce shoot Cd accumulation in leafy vegetables by limiting Cd mobility at both cellular and whole-plant levels.