Cadmium (Cd) stress threatens crop productivity and food safety, and root-level immobilisation is a first-line defence that can limit Cd entry into the symplast and subsequent translocation. The root cell wall constitutes a major apoplastic interface for Cd retention, yet how stress signalling hormones quantitatively modulate cell-wall retention dynamics across genotypes remains poorly defined. Here, we compared two pepper ( Capsicum annuum L.) genotypes with contrasting Cd accumulation (LaYan201 and LaYan101) and examined Cd stress with or without exogenous abscisic acid (ABA). We quantified cell-wall Cd retention using equilibrium isotherms across multiple stress stages and multi-phase adsorption kinetics coupled with diffusion-diagnostic modelling, and integrated day-7 root transcriptomes using WGCNA, protein–protein interaction analysis, and RT–qPCR. Across genotypes, cell-wall Cd binding exhibited pronounced temporal dynamics. LaYan201 displayed slower adsorption but more persistent retention, whereas LaYan101 showed rapid early adsorption followed by earlier saturation. ABA effects were phase-dependent: ABA delayed short-term Cd diffusion/adsorption in kinetic assays, yet increased isotherm-estimated adsorption capacity at intermediate stages in a genotype-specific manner. Co-expression analysis identified a Cd-associated module enriched in metal-transport genes (e.g., HMA, ABCC, PCR, Nramp) and a PME-associated module enriched in cell-wall remodelling genes (e.g., PME/PMEI and GAUT), supporting coordinated regulation of apoplastic retention traits and Cd partitioning processes under stress signalling. Together, these results provide a quantitative, multi-scale framework linking ABA responses to dynamic cell-wall retention phenotypes and candidate regulatory modules in pepper roots under Cd stress, and generate testable hypotheses for how stress signalling integrates cell-wall remodelling and Cd allocation. Under Cd stress, exogenous abscisic acid is associated with coordinated changes in cell-wall remodelling and metal-transport regulation, thereby reshaping Cd retention in pepper roots. Co-expression evidence supports a working model in which PME/PMEI/GAUT -related pectin de-methylesterification and HMA/ABCC/PCR/Nramp -associated Cd distribution contribute to genotype-specific differences in adsorption capacity, kinetic behaviour, and root-to-shoot Cd translocation. • Isotherms, kinetics and WGCNA resolve Cd fixation in pepper roots. • ABA slows early Cd diffusion yet increases mid-stage adsorption capacity. • Contrasting genotypes show adsorption dynamics that explain Cd accumulation. • Coexpression modules link cell-wall remodeling (PME/PMEI/GAUT) and Cd transport. • Model integrates ABA, cell-wall modification and metal transport to limit Cd.
Tu et al. (Wed,) studied this question.