Meeting Abstract
S4.2 Monday, Jan. 4 Plant Movement Mechanisms – Cell Wall Architectures Enable Actuation without Muscles BURGERT, I*; FRATZL, P; Max Planck Institute of Colloids and Interfaces, Potsdam, Germany; Max Planck Institute of Colloids and Interfaces, Potsdam, Germany ingo.burgert@mpikg.mpg.de
Plants are able to adjust the mechanical properties of their tissues to cope with external stresses, and they even generate internal stresses and actuate organ movements. Due to their hierarchical organization, it is mainly the specific cell wall assembly which affects the mechanical performance of the material. By arranging and adapting the orientation of cellulose microfibrils in the cell walls, plants are able to control and to adjust the mechanical properties of their tissues. Moreover the direction of cellulosic fibrils plays a crucial role for internal stress generation and organ movement. The movements of seed dispersal units upon humidity changes are controlled by the architecture of the stiff cellulose fibrils embedded in a swellable matrix. Some impressive examples are pine cones and wheat awns. The fibril design is also explaining the origin of growth stresses in reaction wood of softwoods. Indeed, the microfibril angle by which the cellulose fibrils spiral around the cell lumen controls the anisotropic swelling of the cell wall and, thus, the generation of directed strains and stresses leading to complex bending or torsional movements. Finally, we report on the crucial role of an additional cell wall layer, the so called G-layer, which can be found in leaning stems and branches, in tendrils and contractile roots of a large variety of species. This G-layer consists of almost pure axially oriented and swellable cellulose which enables the plant to generate much higher longitudinal tensile stresses in the G-fibers than in regular fibers. All these examples show the incredible versatility of a system, based on oriented cellulose fibrils in a matrix swelling or shrinking with (ambient) humidity, in constructing actuators providing motility or compensating for external loads.
