Cellulose fibrils direct plant organ movements

Abstract

The secondary plant cell wall is a composite of cellulose and a water-swelling matrix containing hemicelluloses and lignin. Recent experiments showed that this swelling capacity helps generating growth stresses, e.g., in conifer branches or in the stem when subjected to side loads. A similar mechanism also provides motility to wheat seeds. Here we study a simple mechanical model for the cell wall which--in contrast to earlier models--considers extensible cellulose fibrils in an isotropically swelling matrix. Depending on the detailed architecture of the cellulose fibrils, the model predicts that swelling may lead either to significant compressive or tensile stresses or to large movements at low stresses. The model reproduces most of the experimental observations in the wood cells and in the awns of wheat dispersal units. It is also simple enough to provide general guidelines for designing the architecture of fibres in an isotropic swelling medium to generate movements and forces of various kinds and directions.

Self-shaping composites with programmable bioinspired microstructures

“…Shape-changing materials are not very prevalent in synthetic systems but are widespread in nature, particularly in plants [9][10][11][12][13][14][15][16][17][18] . Because of the limited chemical resources and processing conditions, plants have evolved mechanisms that rely on their internal heterogeneous architecture to achieve shape change upon external stimulus [9][10][11][12] .…”

“…Because of the limited chemical resources and processing conditions, plants have evolved mechanisms that rely on their internal heterogeneous architecture to achieve shape change upon external stimulus [9][10][11][12] . Hydration-triggered shape change in natural systems offers a passive, yet dramatic, response with only changes in surrounding humidity levels and is exhibited in diverse seed dispersal units, such as pinecones, wheat awn structures and orchid tree seedpods (Supplementary Movie 1).…”

Pressurized honeycombs as soft-actuators: a theoretical study

“…One explanation for the development of tensile stresses comes from the idea that lateral swelling from the G-layer puts the cell walls under pressure. Owing to the high microfibril angle, these walls translate the hoop stress into a longitudinal tensile stress [17].…”

Actuation systems in plants as prototypes for bioinspired devices

“…The generation of either tensile or compressive stresses depends on different cell geometries and cellulose fibril architecture. The dominating cellulose fibril orientation in normal wood cells and compression wood cells is indicated by inclined lines in the cell wall (after Burgert et al 2007 andFratzl et al 2008). compressive stresses are always generated. Accordingly, the generation of either tensile or compressive stresses is mainly controlled by a clever arrangement of cellulose fibrils in the cell walls .…”