Atomic force microscopy of microfibrils in primary cell walls

Examination of angiosperm primary cell walls by transmission electron microscopy shows that they contain microfibrils that probably consist of cellulose microfibrils surrounded by associated non-cellulosic polysaccharides. Previous studies using solid-state C-13 NMR spectroscopy have shown that the cellulose is all crystalline with crystallites of cross-sectional dimensions of 2-3 nm. However, it is not known if each microfibril contains only one, or more than one crystallite because there is no agreement about the dimensions of the microfibrils. Partially hydrated primary cell walls isolated from onion (Allium cepa L.) and Arabidopsis thaliana (L.) Heynh. were examined by atomic force microscopy and the microfibril diameters determined. The cell walls of both species contained tightly interwoven microfibrils of uniform diameter: 4.4+/-0.13 nm in the onion and 5.8+/-0.17 nm in A. thaliana. The effect was also examined of extracting the A. thaliana cell walls to remove pectic polysaccharides. The microfibrils in the extracted cell walls of A. thaliana were significantly narrower (3.2+/-0.13 nm) than those in untreated walls. The results are consistent with the microfibrils containing only one cellulose crystallite.