Abstract
In higher plant cells, cellulose microfibril and pectin are major components of primacy cell walls in plants, and their mechanical properties are important for cell morphogenesis and maintainance. Some reports had demonstrated that pectin could interact with cellulose microfibrils via arabinan-based pectin RG-I side chains, but the mechanism how arabinan polysaccharides bind to cellulose microfibrils is still unknown. Previously we had identified a novel inhibitor, cobtorin that perturbed the alignment of the cellulose microfibrils. When arabinan was added to medium, cobtorin-induced cell swelling was drastically suppressed. While 1,5-linked linear arabinan backbone had lower efficiency, branched arabinan with 1,2- and/or 1,3-linked arabinofuranosyl side residues strongly suppressed it. Also, treatment with arabinofuranosidase, which catalyzes 1,2- and/or 1,3-linked arabinan side chains, rescued the phenotype, although that with endo-1,5-arabinanase to cleavage 1,5-linked arabinan backbone did not. These results indicate that cobtorin affects branched arabinans in pectin RG-I side chains, and inhibits the interaction between pectin macromolecules and cellulose microfibrils.
