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Molecular and mechanical aspects of helicoid development in plant cell walls

The view is presented that extracellular architecture in plant cell walls results from an interplay between molecular self‐assembly and mechanical reorientation due to growth forces. A key initial self‐assembly step may involve hemicelluloses. It is suggested that hemicelluloses may self‐assemble into a helicoid via a cholesteric liquid crystalline phase; the detailed molecular structure of hemicelluloses (stiff backbone, bulky side chains, and the presence of asymmetric carbon atoms) is shown to be consistent with cholesteric requirements for such self‐assembly. Since hemicelluloses are hydrogen‐bonded to the periphery of cellulose microfibrils, the cellulose could then itself become helicoidally arranged. Such ‘universal plywood’ structure is found in the walls of a wide variety of plants, and in several types of cell (including wood). The permanent effects of growth stresses on patterns seen in sections of helicoids are displayed by computer graphics plots, and the expected changes in stiffness are calculated.