Laboratoire de Mécanique et Génie Civil, CNRS, Université Montpellier 2, 34095 Montpellier, France.
Plant Physiol. 2010 Mar;152(3):1650-8. doi: 10.1104/pp.109.149542. Epub 2010 Jan 13.
Tension wood is widespread in the organs of woody plants. During its formation, it generates a large tensile mechanical stress, called maturation stress. Maturation stress performs essential biomechanical functions such as optimizing the mechanical resistance of the stem, performing adaptive movements, and ensuring long-term stability of growing plants. Although various hypotheses have recently been proposed, the mechanism generating maturation stress is not yet fully understood. In order to discriminate between these hypotheses, we investigated structural changes in cellulose microfibrils along sequences of xylem cell differentiation in tension and normal wood of poplar (Populus deltoides x Populus trichocarpa 'I45-51'). Synchrotron radiation microdiffraction was used to measure the evolution of the angle and lattice spacing of crystalline cellulose associated with the deposition of successive cell wall layers. Profiles of normal and tension wood were very similar in early development stages corresponding to the formation of the S1 and the outer part of the S2 layer. The microfibril angle in the S2 layer was found to be lower in its inner part than in its outer part, especially in tension wood. In tension wood only, this decrease occurred together with an increase in cellulose lattice spacing, and this happened before the G-layer was visible. The relative increase in lattice spacing was found close to the usual value of maturation strains, strongly suggesting that microfibrils of this layer are put into tension and contribute to the generation of maturation stress.
张力木广泛存在于木本植物的器官中。在其形成过程中，它会产生很大的拉伸机械应力，称为成熟应力。成熟应力具有优化茎的机械阻力、执行适应性运动以及确保生长植物的长期稳定性等重要的生物力学功能。尽管最近提出了各种假设，但产生成熟应力的机制尚未完全理解。为了对这些假设进行区分，我们研究了在杨树（Populus deltoides x Populus trichocarpa 'I45-51'）的张力木和正常木中，木质部细胞分化序列中纤维素微纤丝的结构变化。同步辐射微衍射用于测量与连续细胞壁层沉积相关的结晶纤维素的角度和晶格间距的演变。在早期发育阶段，正常木材和张力木材的轮廓非常相似，对应于 S1 和 S2 层的外层形成。在 S2 层中，其内层的微纤角比外层低，特别是在张力木中。只有在张力木中，这种减小伴随着纤维素晶格间距的增加，并且在 G 层可见之前就发生了这种情况。发现晶格间距的相对增加接近成熟应变的常用值，强烈表明该层的微纤丝处于拉伸状态，并有助于产生成熟应力。
