Polysaccharide Structures in the Outer Mucilage of Arabidopsis Seeds Visualised by AFM

Evidence is presented that the polysaccharide rhamnogalacturonan I (RGI) can be biosynthesised in remarkably organised branched configurations, in surprisingly long versions, and can self-assemble into a plethora of structures. AFM imaging has been applied to study the outer mucilage obtained from wild type (WT) and mutant (bxl1-3 and cesa5-1) Arabidopsis thaliana seeds. For WT mucilage, ordered, multi-chain structures of the polysaccharide RGI were observed, with a helical twist visible in favourable circumstances. Molecular dynamics (MD) simulations demonstrated the stability of several possible multi-chain complexes, and the possibility of twisted fibril formation. For bxl1-3 seeds the imaged polymers clearly showed the presence of sidechains. These were surprisingly regular and well organised with an average length of ~ 100 nm and a spacing of ~ 50 nm. The heights of the sidechains imaged were suggestive of single polysaccharide chains, while the backbone was on average four times this height and show...