MODELING THE MECHANICAL-PROPERTIES OF XYLEM TISSUE FROM TOBACCO PLANTS (NICOTIANA-TABACUM SAMSUN) BY CONSIDERING THE IMPORTANCE OF MOLECULAR AND MICROMECHANISMS

Tobacco plants (Nicotiana tabacum 'Samsun') have xylem cell walls whic h are more sensitive to changes in the properties of the matrix than w as predicted using current cell wall mechanical models. A model is pro posed which can account for the importance of the cell wall matrix in determining the modulus of the material. This model is based on a heli cal spring system, with micromechanisms operating at the molecular sca le. Xylem tissue fibre cells can behave as helical springs when the cr osslink density of lignin is low, or they can behave like a composite sheet with fibres at an angle to the applied load when the crosslink d ensity is high. This highlights the importance of molecular modelling when the properties of complex biological materials are being investig ated. (C) 1998 Annals of Botany Company.