Université Clermont Auvergne, INRA, PIAF, Clermont-Ferrand, France.
UMR LERFoB, AgroParisTech, INRA, Nancy, France.
Ann Bot. 2018 May 11;121(6):1151-1161. doi: 10.1093/aob/mcx211.
Trees constantly experience wind, perceive resulting mechanical cues, and modify their growth and development accordingly. Previous studies have demonstrated that multiple bending treatments trigger ovalization of the stem and the formation of flexure wood in gymnosperms, but ovalization and flexure wood have rarely been studied in angiosperms, and none of the experiments conducted so far has used multidirectional bending treatments at controlled intensities. Assuming that bending involves tensile and compressive strain, we hypothesized that different local strains may generate specific growth and wood differentiation responses.
Basal parts of young poplar stems were subjected to multiple transient controlled unidirectional bending treatments during 8 weeks, which enabled a distinction to be made between the wood formed under tensile or compressive flexural strains. This set-up enabled a local analysis of poplar stem responses to multiple stem bending treatments at growth, anatomical, biochemical and molecular levels.
In response to multiple unidirectional bending treatments, poplar stems developed significant cross-sectional ovalization. At the tissue level, some aspects of wood differentiation were similarly modulated in the compressed and stretched zones (vessel frequency and diameter of fibres without a G-layer), whereas other anatomical traits (vessel diameter, G-layer formation, diameter of fibres with a G-layer and microfibril angle) and the expression of fasciclin-encoding genes were differentially modulated in the two zones.
This work leads us to propose new terminologies to distinguish the 'flexure wood' produced in response to multiple bidirectional bending treatments from wood produced under transient tensile strain (tensile flexure wood; TFW) or under transient compressive strain (compressive flexure wood; CFW). By highlighting similarities and differences between tension wood and TFW and by demonstrating that plants could have the ability to discriminate positive strains from negative strains, this work provides new insight into the mechanisms of mechanosensitivity in plants.
树木不断受到风的作用，感知由此产生的机械线索，并相应地改变其生长和发育。先前的研究表明，在裸子植物中，多次弯曲处理会触发茎的椭圆形化和弯曲木的形成，但在被子植物中，椭圆形化和弯曲木很少被研究，迄今为止进行的所有实验都没有使用受控强度的多向弯曲处理。假设弯曲涉及拉伸和压缩应变，我们假设不同的局部应变可能会产生特定的生长和木质部分化反应。
在 8 周的时间里，对幼杨树茎的基部进行多次瞬时受控单向弯曲处理，从而可以区分在拉伸或压缩弯曲应变下形成的木材。这种设置使我们能够在生长、解剖学、生物化学和分子水平上对杨树茎对多次茎弯曲处理的局部响应进行分析。
对多次单向弯曲处理的响应，杨树茎形成了显著的横截面椭圆形化。在组织水平上，木质部分化的某些方面在压缩区和拉伸区得到了类似的调节（导管频率和无 G 层纤维的直径），而其他解剖特征（导管直径、G 层形成、有 G 层纤维的直径和微纤丝角）和 fasciclin 编码基因的表达在两个区中则有差异调节。
这项工作使我们提出了新的术语来区分响应多向弯曲处理产生的“弯曲木”与响应瞬时拉伸应变（拉伸弯曲木；TFW）或瞬时压缩应变（压缩弯曲木；CFW）产生的木材。通过突出张力木和 TFW 之间的相似性和差异，并证明植物能够区分正应变和负应变，这项工作为植物的机械敏感性机制提供了新的见解。
