Cell wall charge gates iron availability in plant roots
Plants acquire essential mineral nutrients from the soil, yet these elements must first traverse the extracellular matrix of the root before reaching the cell surface. How the physical properties of this extracellular compartment influence nutrient distribution and availability remains poorly understood. In plants, this extracellular matrix is formed by the cell wall, which carries a dynamically regulated negative charge that can change during development and in response to environmental cues. Here we demonstrate that cell wall charge functions as a tunable electrostatic gate that determines how iron is partitioned between retention and bioavailability. This decoupling between iron abundance and availability reveals a fundamental tradeoff imposed by extracellular electrostatics. A mechanistic diffusion-binding model shows that increasing wall charge inherently enhances iron sequestration while limiting its mobility at the cell surface. Genetic perturbation of pectin de-methylesterification validates this principle in vivo. Moreover, iron limitation itself triggers active remodeling of cell wall charge, dynamically shifting the balance toward increased iron accessibility. Together, these findings identify the plant cell wall as an active regulator of nutrient homeostasis rather than a passive barrier. By dynamically modulating extracellular electrostatics, roots control iron partitioning and bioavailability, uncovering a new physical layer of regulation in plant mineral nutrition. One-Sentence SummaryThe plant cell wall operates as a tunable electrostatic gate that buffers and releases iron through spatially and environmentally regulated charge dynamics.