Mechanics of plant epidermal cell wall: effect of anisotropic alignment of cellulose microfibrils in the junction region

In plants, cellulose microfibrils (CMFs) play a major role in cell wall mechanics. Plant epidermal peels have been widely used as a model system to study the relationship between the CMF arrangement and the mechanical properties of the cell wall. Recently, vibrational sum frequency generation (SFG) spectroscopy imaging has discovered that CMFs in the cell–cell junction regions (i.e., edges of each cell) in the periclinal wall are preferentially aligned (anisotropic) perpendicular to the anticlinal plane, while those in the face regions have the crossed-polylamellate (isotropic) structure possessing all possible orientations. Here, we studied the effect of these regiospecific CMF orientations on the tensile properties of peeled plant epidermal cell walls using finite element analysis (FEA). The FEA simulation showed that the anisotropic fibers in the junction region of the elongated hexagonal cells amplified the anisotropy in the mechanical behavior of the wall under tensile stretching and exhibited a strain-dependent Poisson’s ratio with nonlinear mechanical behavior. The SFG analysis suggested that, in the junction region, there are alterations in cellulose chain conformation within CMFs and/or in CMF-CMF bundling upon tensile stretch.