Micromechanics of plant tissues beyond the linear-elastic range

Abstract

We investigated the relation between cell wall structure and the resulting mechanical characteristics of different plant tissues. Special attention was paid to the mechanical behaviour beyond the linear-elastic range, the underlying micromechanical processes and the fracture characteristics. The previously proposed model of reorientation and slippage of the cellulose microfibrils in the cell wall [H.-CH. Spatz et al. (1999) J Exp Biol 202:3269-3272) was supported and is here refined, using measurements of the changes in microfibrillar angle during straining. Our model explains the widespread phenomenon of stress-strain curves with two linear portions of different slope and sheds light on the micromechanical processes involved in viscoelasticity and plastic yield. We also analysed the velocity dependence of viscoelasticity under the perspective of the Kelvin model, resolving the measured viscoelasticity into functions of a velocity-dependent and a velocity-independent friction. The influence of lignin on the above-mentioned mechanical properties was examined by chemical lignin extraction from tissues of Aristolochia macrophylla Lam. and by the use of transgenic plants of Arabidopsis thaliana (L.) Heynh. with reduced lignin content. Additionally, the influence of extraction of hemicelluloses on the mechanical properties was investigated as well as a cell wall mutant of Arabidopsis with an altered configuration of the cellulose microfibrils.

Mechanical Function of Lignin and Hemicelluloses in Wood Cell Wall Revealed with Microtension of Single Wood Fiber

“…As shown previously (Beismann et al 2000;Köhler and Spatz 2002), the character of the fracture surface is an indication of the micromechanical processes. We investigated the fracture characteristics of dry mechanically isolated fibers and different chemical treated isolated fibers, as shown in Fig.…”

Micromechanical properties of common yew (Taxus baccata) and Norway spruce (Picea abies) transition wood fibers subjected to longitudinal tension

“…9 Furthermore, a biphasic stress-strain curve, as found for yew fi bers, is a common phenomenon among plant tissues with high microfi bril angles in the S2 layer. [10][11][12][13] It indicates an extraordinary longitudinal toughness of yew fi bers because plastic deformation considerably contributes to their high strain to fracture. The larger MFA of yew fi bers might also cause their slightly lower ultimate tensile stress.…”

Within Tree Variation of Lignin, Extractives, and Microfibril Angle Coupled With the Theoretical and Near Infrared Modeling of Microfibril Angle

“…A high microfibril angle and lignin content is needed to resist gravity and wind loads for young trees Reiterer et al 1999). Also, a high microfibril angle incorporates extensibility needed during wind loading while increased lignin adds stiffness resistance to compression forces (Hepworth & Vincent 1998; 2000, Kohler & Spatz 2002).…”