Department of Mechanical Engineering, McGill University, 817 Sherbrooke Street West, Montréal, QC, H3A 0C3, Canada.
Theoretical and Applied Mechanics Program, School of Engineering and Applied Science, Northwestern University, 2145 Sheridan Rd., Evanston, IL, 60208-3109, USA.
Sci Rep. 2020 Jan 16;10(1):506. doi: 10.1038/s41598-019-57365-z.
As a physical response to water loss during drought, inner Selaginella lepidophylla stems curl into a spiral shape to prevent photoirradiation damage to their photosynthetic surfaces. Curling is reversible and involves hierarchical deformation, making S. lepidophylla an attractive model with which to study water-responsive actuation. Investigation at the organ and tissue level has led to the understanding that the direction and extent of stem curling can be partially attributed to stiffness gradients between adaxial and abaxial stem sides at the nanoscale. Here, we examine cell wall elasticity to understand how it contributes to the overall stem curling. We compare the measured elastic moduli along the stem length and between adaxial and abaxial stem sides using atomic force microscopy nano-indentation testing. We show that changes in cortex secondary cell wall development lead to cell wall stiffness gradients from stem tip to base, and also between adaxial and abaxial stem sides. Changes in cortical cell wall morphology and secondary cell wall composition are suggested to contribute to the observed stiffness gradients.
作为干旱期间水分流失的一种物理响应，内生卷柏茎卷曲成螺旋状，以防止光合面受到光照射损伤。卷曲是可逆的，涉及到层次变形，使卷柏成为研究水响应致动的有吸引力的模型。在器官和组织水平的研究导致人们理解到，茎卷曲的方向和程度部分归因于纳米尺度上茎的腹侧和背侧之间的硬度梯度。在这里，我们研究细胞壁弹性，以了解它如何促成整体茎卷曲。我们使用原子力显微镜纳米压痕测试比较了沿茎长以及腹侧和背侧茎侧的测量弹性模量。我们表明，皮层次生细胞壁发育的变化导致从茎尖到底部以及腹侧和背侧茎侧的细胞壁硬度梯度。皮层细胞壁形态和次生细胞壁组成的变化被认为导致了观察到的硬度梯度。
