Novel roles of hydrogen peroxide (H 2 O 2 ) in regulating pectin synthesis and demethylesterification in the cell wall of rice ( Oryza sativa ) root tips

Summary Hydrogen peroxide (H 2 O 2 ) has been reported to increase lignin formation, enhance cell wall rigidification, restrict cell expansion and inhibit root elongation. However, our results showed that it not only inhibited rice ( Oryza sativa ) root elongation, but also increased root diameter. No study has reported how and why H 2 O 2 increases cell expansion and root diameter. Exogenous H 2 O 2 and its scavenger 4‐hydroxy‐Tempo were applied to confirm the roles of H 2 O 2 . Immunofluorescence, fluorescence probe, ruthenium red staining, histological section and spectrophotometry were used to monitor changes in the degree of pectin methylesterification, pectin content, pectin methylesterase ( PME ) activity and H 2 O 2 content. Exogenous H 2 O 2 inhibited root elongation, but increased cell expansion and root diameter significantly. H 2 O 2 not only increased the region of pectin synthesis and pectin content in root tips, but also increased PME activity and pectin demethylesterification. The scavenger 4‐hydroxy‐Tempo reduced root H 2 O 2 content and recovered H 2 O 2 ‐induced increases in cell expansion and root diameter by inhibiting pectin synthesis, PME activity and pectin demethylesterification. H 2 O 2 plays a novel role in the regulation of pectin synthesis, PME activity and pectin demethylesterification. H 2 O 2 increases cell expansion and root diameter by increasing pectin content and demethylesterification.