Department of Life Sciences, Ben-Gurion University of the Negev, Beer Sheva, Israel.
Ann Bot. 2014 Apr;113(5):789-97. doi: 10.1093/aob/mcu002. Epub 2014 Feb 15.
Cables composed of long, non-lignified fibre cells enclosed in a cover of much shorter thin-walled, crystal-containing cells traverse the air chambers (lacunae) in leaves of the taller species of Typha. The non-lignified fibre cables are anchored in diaphragms composed of stellate cells of aerenchyma tissue that segment the long air chambers into smaller compartments. Although the fibre cables are easily observed and can be pulled free from the porous-to-air diaphragms, their structure and function have been ignored or misinterpreted.
Leaves of various species of Typha were dissected and fibre cables were pulled free and observed with a microscope using bright-field and polarizing optics. Maximal tensile strength of freshly removed cables was measured by hanging weights from fibre cables, and Instron analysis was used to produce curves of load versus extension until cables broke.
Polarized light microscopy revealed that the cellulose microfibrils that make up the walls of the cable fibres are oriented parallel to the long axis of the fibres. This orientation ensures that the fibre cables are mechanically stiff and strong under tension. Accordingly, the measured stiffness and tensile strength of the fibre cables were in the gigapascal range. In combination with the dorsal and ventral leaf surfaces and partitions that contain lignified fibre bundles and vascular strands that are strong in compression, the very fine fibre cables that are strong under tension form a tensegrity structure. The tensegrity structure creates multiple load paths through which stresses are redistributed throughout the 1-3 m tall upright leaves of Typha angustifolia, T. latifolia, T. × glauca, T. domingensis and T. shuttleworthii. The length of the fibre cables relative to the length of the leaf blades is reduced in the last-formed leaves of flowering individuals. Fibre cables are absent in the shorter leaves of Typha minima and, if present, only extend for a few centimetres from the sheath into the leaf blade of Typha laxmannii. The advantage of the structure of the Typha leaf blade, which enables stiffness to give way to flexibility under windy conditions, is discussed for both vegetative and flowering plants.
由长的非木质化纤维细胞组成的缆索，被包裹在一层短得多的薄壁、含晶体细胞中，穿过叶片中的空气腔（腔隙）。非木质化纤维缆索锚定在由通气组织的星状细胞组成的隔膜中，这些隔膜将长的空气腔分隔成更小的隔室。尽管纤维缆索很容易被观察到，并且可以从多孔的空气隔膜中拉出来，但它们的结构和功能一直被忽视或误解。
解剖各种种类的香蒲叶，将纤维缆索拉出来，用显微镜在明场和偏光下观察。通过悬挂重物从纤维缆索上测量新鲜取出的缆索的最大拉伸强度，并使用 Instron 分析产生负载与延伸的曲线，直到缆索断裂。
偏光显微镜显示，构成缆索纤维壁的纤维素微纤维沿纤维的长轴平行排列。这种取向确保纤维缆索在张力下具有机械刚性和强度。因此，纤维缆索的测量刚度和拉伸强度在千兆帕斯卡范围内。与含有木质化纤维束和在压缩下坚固的维管束的背侧和腹侧叶片表面以及分隔物相结合，在张力下坚固的非常细的纤维缆索形成了一种张拉整体结构。张拉整体结构创建了多个载荷路径，通过这些路径，应力在 1-3 米高的直立香蒲叶中重新分布，包括狭叶香蒲、长苞香蒲、杂交香蒲、多穗香蒲和香蒲。在开花个体的最后形成的叶片中，纤维缆索的长度相对于叶片长度缩短。在矮小香蒲的较短叶片中不存在纤维缆索，如果存在，也只是从鞘延伸几厘米到叶片中。讨论了香蒲叶片结构的优势，该结构在有风的条件下能够使刚度向柔韧性转变，这对营养植物和开花植物都有好处。
