How do cell walls regulate plant growth?
The cell wall of growing plant tissues has frequently been interpreted in terms of inextensible cellulose microfibrils tethered by hemicellulose polymers attached to the microfibril surface by hydrogen bonds, with growth occurring when tethers are broken or peeled off the microfibril surface by expansins. This has sometimes been described as the sticky network model. In this paper, a number of theoretical difficulties with this model, and discrepancies between predicted behaviour and observations by a number of researchers, are noted. (i) Predictions of cell wall moduli, based upon the sticky network model, suggest that the cell wall should be much weaker than is observed. (ii) The maximum hydrogen bond energy between tethers and microfibrils is less than the work done in expansion and therefore breakage of such hydrogen bonds is unlikely to limit growth. (iii) Composites of bacterial cellulose with xyloglucan are weaker than pellicles of pure cellulose so that it seems unlikely that h
