Abstract text: Boron is essential for plant cell wall structure, primarily through its role in stabilizing the pectic network. Rhamnogalacturonan-II (RG-II) domain of pectin forms a borate ester cross-linked dimer crucial for proper cell wall formation. Boronic acids can also form reversible ester bonds with cis-diols, like borates, but previous studies have produced conflicting conclusions about whether they promote or inhibit RG-II dimer formation in plants.In this study, B-deficient suspension-cultured rose cells were used to investigate the role of boronic acids in RG-II dimerization. Cells grown in presence of boronic acids were able to form RG-II dimers in vivo. However, in vitro experiments showed that RG-II monomers did not form dimers when reacted with alkyl or aryl boronic acids. The discrepancy was explained by the discovery that hydrogen peroxide (H₂O₂) can oxidatively deboronate boronic acids, converting them into boric acid, which then enables RG-II dimer formation. NMR analysis and DFT calculations further clarified the mechanism and energetics of this oxidation process. Overall, results indicate that externally supplied boronic acids can act as indirect sources of boric acid in plants. However, the deboronation reaction also produces alcohol by-products that may undergo further modification in plants, potentially contributing to observed growth and developmental defects.