Direct visualization of straw cell walls by AFM.

The structural relationship of cellulose, hemicellulose, and lignin in plant cell walls is still a mystery needing to be explored. By using atomic force microscopy (AFM) the surface of straw at different layers was directly observed, and the structural characteristics were analyzed by topographic analysis and FT-IR spectra. It was found that a compact layer of wax covered the outside of the straw, which protects the straw from insects and microorganisms. At the boundary of the primary and second wall there appears a network structure of cellulose and hemicellulose, with some lignin localised on the surface of the network. It is consistent with the model of a cell wall suggested by Vincent. Inside the second cell wall, there is a layer mainly composed of a cellulose crystalline region. High-resolution AFM observation reveals that the crystalline structure consists of both triclinic and monoclinic unit cells. An AFM phase image showing the structural relation between cellulose microfibrils, hemicellulose, and lignin in the straw cell wall.