Cell wall thickening in developing tension wood of artificially bent poplar trees

Abstract

Trees can control their shape and resist gravity thanks to their ability to produce wood under tensile stress. This stress is known to be produced during the maturation of wood fibres but the mechanism of its generation remains unclear. This study focuses on the formation of the secondary wall in tension wood produced in artificially tilted poplar saplings. Thickness of secondary wall layer (SL) and gelatinous layer (GL) were measured from cambium to mature wood in several trees sampled at different times after tilting. Measurements on wood fibres produced before tilting show the progressive increase of secondary wall thickness during the growing season. After the tilting date, SL thickness decreased markedly from normal wood to tension wood while the total thickness increased compared to normal wood, with the development of a thick GL. However, even after GL formation, SL thickness continues to increase during the growing season. GL thickening was observed to be faster than SL thickening. The development of the unlignified GL is proposed to be a low cost, efficient strategy for a fast generation of tensile stress in broadleaved trees.

Diversity in the organisation and lignification of tension wood fibre walls – A review

“…Finally, Araki et al (1983) also found the third type, but only in the transition zone between normal wood and tension wood. This is in agreement with the results of Abedini et al (2015) on poplar, in which the authors reported the establishment of a G-layer on an S 2 layer formed before the tilting of the tree. It could therefore be hypothesised that in the study by Araki et al (1983) the S 3 layer was formed just before tilting and the formation of a G-layer, thus explaining the presence of the organisation S 1 +S 2 +S 3 +G in the transition zone only.…”

Influence of force volume indentation parameters and processing method in wood cell walls nanomechanical studies

“…In tension wood, which is generated by angiosperms to reorient their axes through the generation of internal tensile stress during the maturation of new cells, sometimes a specific layer called “gelatinous” (G layer) (Fig. 1 b) replaces or is added to the S2 7 – 10 . This layer is composed of a higher amount of crystalline cellulose almost aligned with the direction of the fiber (MFA close to 0°) and of mostly hemicellulose for the matrix 7 , 8 , 10 , 11 .…”

Poplar woody taproot under bending stress: the asymmetric response of the convex and concave sides

“…The morphology, anatomy and ultrastructure of TW have been extensively studied (reviewed by Ruelle et al, 2014), and it is well known that TW is less lignified, has more longitudinally oriented cellulose microfibrils, and higher cellulose crystallinity and content than normal wood. Furthermore, the cell wall structure of TW exhibits the formation of a specialized gelatinous wall layer which has been proposed to be a low-cost, efficient strategy for the fast generation of tensile stress in broadleaved trees (Abedini et al, 2015). The wood produced on the side of a stem or branch opposite to the reaction wood is named opposite wood (OW) and is characterized by properties intermediate between normal and reaction wood (Timell, 1986).…”