Plants have evolved a multitude of mechanisms to actuate organ movement. The osmotic influx and efflux of water in living cells can cause a rapid movement of organs in a predetermined direction. Even dead tissue can be actuated by a swelling or drying of the plant cell walls. The deformation of the organ is controlled at different levels of tissue hierarchy by geometrical constraints at the micrometre level (e.g. cell shape and size) and cell wall polymer composition at the nanoscale (e.g. cellulose fibril orientation). This paper reviews different mechanisms of organ movement in plants and highlights recent research in the field. Particular attention is paid to systems that are activated without any metabolism. The design principles of such systems may be particularly useful for a biomimetic translation into active technical composites and moving devices.

Actuation systems in plants as prototypes for bioinspired devices

The mechanical performance of wood and wood products is highly dependent on the structural arrangement and properties of the polymers within the fibre cell wall. To improve utilisation and manufact ...

Cell wall features with regard to mechanical performance. A review. : COST Action E35 2004-2008 : Wood machining - Micromechanics and fracture

Summary
• Fifteen poplar cDNA encoding fasciclin-like arabinogalactan proteins (PopFLAs) were finely characterized, whereas the presence of arabinogalactan proteins (AGPs) was globally assessed during wood formation.
• PopFLAs transcript accumulation was analysed through EST distribution in cDNA libraries, semi-quantitative RT-PCR, microarray experiment and Northern blot analysis. Similarly, AGPs contents were globally quantified by rocket electrophoresis. AGPs accumulation was further examined by Western blotting and immunocytolocalization.
• Ten PopFLAs were specifically expressed in tension wood (TW) and not expressed in the cambial zone. Rocket electrophoresis revealed important AGPs accumulation in TW xylem. An anti-AGPs specific antibody recognized two proteins preferentially present in the cell wall-bound fraction from TW. Immunocytochemistry revealed a strong labelling close to the inner part of the G-layer of TW fibres.
• PopFLAs are expressed in xylem and many are up-regulated in TW. It is suggested that some PopFLAs accumulating at the inner side of the G-layer may have a specific function in the building of this layer. PopFLAs expression may therefore be linked to the specific mechanical properties of TW.

Poplar genes encoding fasciclin‐like arabinogalactan proteins are highly expressed in tension wood

Gelatinous fibres are specialized fibres, distinguished by the presence of an inner, gelatinous cell-wall layer. In recent years, they have attracted increasing interest since their walls have a desirable chemical composition (low lignin, low pentosan, and high cellulose contents) for applications such as saccharification and biofuel production, and they have interesting mechanical properties, being capable of generating high tensional stress. However, the unique character of gelatinous layer has not yet been widely recognized. The first part of this review presents a model of gelatinous-fibre organization and stresses the unique character of the gelatinous layer as a separate type of cell-wall layer, different from either primary or secondary wall layers. The second part discusses major current models of tensional stress generation by these fibres and presents a novel unifying model based on recent advances in knowledge of gelatinous wall structure. Understanding this mechanism could potentially lead to novel biomimetic developments in material sciences.

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Tensional stress generation in gelatinous fibres: a review and possible mechanism based on cell-wall structure and composition

Lignification and tension wood

Afin de clarifier le role joue par les microfibrilles dans la genese des contraintes de croissance dans l'arbre, une analyse experimentale a ete realisee sur 7 essences feuillues des Appalaches produisant ou non des fibres gelatineuses dans la partie superieure des tiges inclinees. Dans le cas des essences produisant des fibres gelatineuses, des contraintes elevees sont observees au niveau des zones a forte proportion surfacique de couches gelatineuses en section transverse. Pour les essences ne produisant pas de fibres gelatineuses, la contrainte longitudinale de tension est d'autant plus grande que l'angle des microfibrilles est petit [...]

/pdf/growth-stresses-in-tension-wood-role-of-microfibrils-and-amkui4yo8j.pdf

RR Archer

Papers

Growth stresses in tension wood: role of microfibrils and lignification