Novel roles of hydrogen peroxide (H2O2) in regulating pectin synthesis and demethylesterification in the cell wall of rice (Oryza sativa) root tips

Hydrogen peroxide (H2O2) 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 H2O2 increases cell expansion and root diameter. Exogenous H2O2 and its scavenger 4-hydroxy-Tempo were applied to confirm the roles of H2O2. 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 H2O2 content. Exogenous H2O2 inhibited root elongation, but increased cell expansion and root diameter significantly. H2O2 not only increased the region of pectin synthesis and pectin content in roottips, but also increased PME activity and pectin demethylesterification. The scavenger 4-hydroxy-Tempo reduced root H2O2 content and recovered H2O2-induced increases in cell expansion and root diameter by inhibiting pectin synthesis, PME activity and pectin demethylesterification. H2O2 plays a novel role in the regulation of pectin synthesis, PME activity and pectin demethylesterification. H2O2 increases cell expansion and root diameter by increasing pectin content and demethylesterification.