Anatomía, Fisiología y Genética vegetal, ETSI Montes, Universidad Politécnica de Madrid, Spain.
J Exp Bot. 2014 May;65(8):1997-2008. doi: 10.1093/jxb/eru045. Epub 2014 Feb 20.
When tree stems are mechanically stimulated, a rapid long-distance signal is induced that slows down primary growth. An investigation was carried out to determine whether the signal might be borne by a mechanically induced pressure pulse in the xylem. Coupling xylem flow meters and pressure sensors with a mechanical testing device, the hydraulic effects of mechanical deformation of tree stem and branches were measured. Organs of several tree species were studied, including gymnosperms and angiosperms with different wood densities and anatomies. Bending had a negligible effect on xylem conductivity, even when deformations were sustained or were larger than would be encountered in nature. It was found that bending caused transient variation in the hydraulic pressure within the xylem of branch segments. This local transient increase in pressure in the xylem was rapidly propagated along the vascular system in planta to the upper and lower regions of the stem. It was shown that this hydraulic pulse originates from the apoplast. Water that was mobilized in the hydraulic pulses came from the saturated porous material of the conduits and their walls, suggesting that the poroelastic behaviour of xylem might be a key factor. Although likely to be a generic mechanical response, quantitative differences in the hydraulic pulse were found in different species, possibly related to differences in xylem anatomy. Importantly the hydraulic pulse was proportional to the strained volume, similar to known thigmomorphogenetic responses. It is hypothesized that the hydraulic pulse may be the signal that rapidly transmits mechanobiological information to leaves, roots, and apices.
当树干受到机械刺激时，会诱导出一种快速的长距离信号，从而减缓初生生长。本研究旨在确定该信号是否可能由木质部中的机械诱导压力脉冲承载。通过将木质部流量计和压力传感器与机械测试装置耦合，可以测量树干和树枝机械变形的水力效应。研究了几种树种的器官，包括具有不同木材密度和解剖结构的裸子植物和被子植物。弯曲对木质部导电性的影响可以忽略不计，即使变形是持续的或大于自然界中可能遇到的变形。研究发现，弯曲会导致树枝段木质部内的液压短暂变化。这种木质部内的局部瞬时压力增加会迅速沿植物体内的脉管系统传播到茎的上下区域。结果表明，这种液压脉冲起源于质外体。在液压脉冲中动员的水来自导管及其壁的饱和多孔材料，这表明木质部的多孔弹性行为可能是一个关键因素。尽管这可能是一种通用的机械响应，但不同物种之间发现了液压脉冲的定量差异，这可能与木质部解剖结构的差异有关。重要的是，液压脉冲与应变体积成正比，类似于已知的向触性形态发生响应。因此，液压脉冲可能是将机械生物学信息快速传递到叶片、根系和顶端的信号。
