Boron-Mediated Inhibition of Cadmium Uptake in Crops: Mechanisms of Apoplastic Barrier Reinforcement and Transmembrane Transport Regulation

Soil cadmium (Cd) contamination pose a serious threat to global food safety. Boron (B) application effectively reduces Cd accumulation in crops via a dual defense mechanism. This review synthesizes the mechanisms of apoplastic barrier reinforcement and transmembrane transport regulation in plants. B promotes pectin biosynthesis, cross-linking and demethylation of the cell wall to immobilize more Cd²⁺. It also stimulates the deposition of lignin in the Casparian strip, physically blocking Cd²⁺ entry into the stele of rice, hot pepper and rape. Additionally, B acts as a transcriptional regulator to downregulate influx transporters (e.g., <i>NRAMP1</i>, <i>IRT1</i>) located at the plasma membrane. Consequently, the expression of vacuolar sequestration transporters (e.g., <i>HMA3</i>, <i>ABCC2</i>) is suppressed, reflecting an adaptive response to reduced cytosolic Cd. The concept of "external exclusion and influx inhibition" provides a theoretical basis for implementing B-based agronomic practices as a strategy to inhibit Cd uptake, ensuring safer food production in Cd-contaminated soils.