The
cell walls constitute the mechanical support of plants. Crystalline cellulose
building the walls forms rigid microfibrils that set the stiffness of the cell,
and its expansion directionality during growth. Therefore, the determination of
the microfibrils' directions is important in both mechanical and developmental
assays.We
adapted polarized light microscopy to estimate the cellulose microfibril orientations
in sub-cellular resolution. The optical information supplements X-ray
scattering data, Raman micro-spectroscopy, and electron microscopy. We
analyze an Araucaria excels R.
Br. branch in which we reveal lower cellulose density at regions where the cell
wall curvature becomes bigger, namely, the cell wall corners. We show that a wheat awn’s hygroscopically-active
region exhibits a gradient in the cellulose microfibril angles that spans across
four cell rows. Finally, we reveal that in a stork's bill’s (Erodium gruinum L.) coiling awn, the cellulose in the cell wall is organized in two orientations
seamed together, rather than in a continuous helix. The
unique spatial information is easily obtained from microscopic specimens and
further illuminates new aspects in mechanical tissues.
