Microfibrils build architecture : a geometrical model

Several mechanisms for cellulose microfibril (CMF) orientation have been proposed, of which guidance by cortical microtubules is widely accepted for growing cells, but in many non-growing cells CMF orientations are not correlated to microtubule arrangement. We have formulated a theory for wall deposition consitent with present day experimental data on walls and cellular processes. It appeals to a very generic origin, geometrical constraints, as the underlying cause of cell wall architecture. This is a fully mathematical model, allowing for specific predictions of qualitative and quantitative nature. It was formulated on the basis of extensive observations on the helicoidal wall texture of Equisetum hyemale root hairs. The key point of the geometrical theory is the coupling of the CMF synthase, i.e. rosette, trajectories to the density of rosettes. This provides the cell with a route to manipulate the wall structure by creating controlled local variations of the number of active rosettes. We discuss how the model can describe known wall textures, underlining the flexibility of the proposed mechanism.