Using Viscoelastic Properties of the Woody Tissue from Tobacco Plants (Nicotiana tabacum) to Comment

Annals of Botany 81: 729–734, 1998Using Viscoelastic Properties of the Woody Tissue from Tobacco Plants(Nicotiana tabacum) to Comment on the Molecular Structure of Cell WallsD.G.HEPWORTH*, J.F.V.VINCENT* and W.SCHUCH‹*Centre for Biomimetics, Earley Gate, TOB1, Reading UniŠersity, Reading RG6 2AT and ‹ Zeneca Seeds,Jealott’s Hill Research Station, Bracknell RG12 6EYReceived: 13 October 1977 Returned for revision: 5 January 1988 Accepted: 17 February 1998Lignin in the cell walls of woody tissue has a much lower crosslink density in tobacco wood than in tree wood. Thiscauses tobacco wood to show very different viscoelastic behaviour. With the aid of genetically modified plants, it isshown that the lignin in tobacco plant cell walls behaves in much the same way as a polymer solution. It exhibits bothrate stiffening and rate thinning behaviour due to the entangled nature of the lignin networks. The hydrophobicportions of lignin have a very low polymer chain crosslink density, hence entanglements make a significantcontribution. # 1998 Annals of Botany CompanyKey words: Tobacco plants, lignin, polymer solution, shear thinning, stress relaxation.Birkinshaw et al. (1989) identified two tan d peaks inINTRODUCTIONtemperature scans ranging from fi150 to 150 °C. However,Plant cell walls are viscoelastic and the Young’s moduli are in all cases tan d never fell below 0–01, and above fi50 °Crate dependent (Preston, 1974; Wainwright et al., 1976; was always above 0–02. Thus ...