Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139.
Department of Biology, Pennsylvania State University, University Park, Pennsylvania 16802.
Plant Physiol. 2017 Dec;175(4):1593-1607. doi: 10.1104/pp.17.01270. Epub 2017 Oct 30.
At early stages of Arabidopsis () flowering, the inflorescence stem undergoes rapid growth, with elongation occurring predominantly in the apical ∼4 cm of the stem. We measured the spatial gradients for elongation rate, osmotic pressure, cell wall thickness, and wall mechanical compliances and coupled these macroscopic measurements with molecular-level characterization of the polysaccharide composition, mobility, hydration, and intermolecular interactions of the inflorescence cell wall using solid-state nuclear magnetic resonance spectroscopy and small-angle neutron scattering. Force-extension curves revealed a gradient, from high to low, in the plastic and elastic compliances of cell walls along the elongation zone, but plots of growth rate versus wall compliances were strikingly nonlinear. Neutron-scattering curves showed only subtle changes in wall structure, including a slight increase in cellulose microfibril alignment along the growing stem. In contrast, solid-state nuclear magnetic resonance spectra showed substantial decreases in pectin amount, esterification, branching, hydration, and mobility in an apical-to-basal pattern, while the cellulose content increased modestly. These results suggest that pectin structural changes are connected with increases in pectin-cellulose interaction and reductions in wall compliances along the apical-to-basal gradient in growth rate. These pectin structural changes may lessen the ability of the cell wall to undergo stress relaxation and irreversible expansion (e.g. induced by expansins), thus contributing to the growth kinematics of the growing stem.
在拟南芥开花的早期阶段，花序茎经历快速生长，主要在茎的顶端约 4 厘米处伸长。我们测量了伸长率、渗透压、细胞壁厚度和细胞壁机械柔顺性的空间梯度，并将这些宏观测量结果与使用固态核磁共振波谱和小角中子散射对花序细胞壁的多糖组成、流动性、水合作用和分子间相互作用的分子水平表征相结合。力-伸长曲线显示，在伸长区，细胞壁的塑性和弹性柔顺性从高到低呈梯度分布，但生长速率与壁柔顺性的关系图非常呈非线性。中子散射曲线仅显示细胞壁结构的细微变化，包括纤维素微纤维取向沿生长茎略微增加。相比之下，固态核磁共振谱显示出果胶含量、酯化度、分支度、水合作用和流动性在顶端到基部呈显著减少的模式，而纤维素含量略有增加。这些结果表明，果胶结构的变化与细胞壁柔顺性的降低以及果胶-纤维素相互作用的增加有关，这与生长速率的顶端到基部梯度有关。这些果胶结构的变化可能会降低细胞壁进行应力松弛和不可逆膨胀（例如由膨胀素诱导）的能力，从而有助于生长中的茎的生长运动学。
