Abscisic acid modulates genotype-specific root cell-wall cadmium retention in pepper: evidence from adsorption...

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.