Excessive iron deposition in root apoplast is involved in growth arrest of roots in response to proton stress.

The rhizotoxicity of protons (H+) in acidic soils is a fundamental constraint that results in serious yield losses. However, the mechanisms underlying H+-mediated inhibition of root growth are poorly understood. In this study, we revealed that H+-induced root growth inhibition depends considerably on excessive iron deposition in root apoplasts. Reducing such aberrant iron deposition by decreasing the iron supply or disrupting the ferroxidases LOW PHOSPHATE ROOT 1 (LPR1) and LOW PHOSPHATE ROOT 2 (LPR2) attenuates the inhibitory effect of H+ on primary root growth efficiently. Further analysis showed that excessive iron deposition triggers a burst of highly reactive oxygen species, consequently impairing normal root development. Our study uncovered a valuable strategy for improving the ability of plants to tolerate H+ toxicity by manipulating iron availability.