Botany and Plant Science and Ryan Institute for Environmental, Marine and Energy Research, School of Natural Sciences, National University of Ireland, Galway, University Road, Galway, Ireland.
Planta. 2013 Jun;237(6):1453-64. doi: 10.1007/s00425-013-1856-6. Epub 2013 Feb 22.
Laminae of Adiantum raddianum Presl., a fern belonging to the family Pteridaceae, are characterised by the presence of epidermal fibre-like cells under the vascular bundles. These cells were thought to contain silica bodies, but their thickened walls leave no space for intracellular silica suggesting it may actually be deposited within their walls. Using advanced electron microscopy in conjunction with energy dispersive X-ray microanalysis we showed the presence of silica in the cell walls of the fibre-like idioblasts. However, it was specifically localised to the outer layers of the periclinal wall facing the leaf surface, with the thick secondary wall being devoid of silica. Immunocytochemical experiments were performed to ascertain the respective localisation of silica deposition and glycan polymers. Epitopes characteristic for pectic homogalacturonan and the hemicelluloses xyloglucan and mannan were detected in most epidermal walls, including the silica-rich cell wall layers. The monoclonal antibody, LM6, raised against pectic arabinan, labelled the silica-rich primary wall of the epidermal fibre-like cells and the guard cell walls, which were also shown to contain silica. We hypothesise that the silicified outer wall layers of the epidermal fibre-like cells support the lamina during cell expansion prior to secondary wall formation. This implies that silicification does not impede cell elongation. Although our results suggest that pectic arabinan may be implicated in silica deposition, further detailed analyses are needed to confirm this. The combinatorial approach presented here, which allows correlative screening and in situ localisation of silicon and cell wall polysaccharide distribution, shows great potential for future studies.
凤尾蕨科凤尾蕨属植物的叶片的维管束下有表皮纤维状细胞。这些细胞被认为含有硅体，但它们增厚的细胞壁没有为细胞内的硅留出空间，这表明硅可能实际上沉积在细胞壁内。我们使用先进的电子显微镜结合能量色散 X 射线微分析，证明了纤维状异形细胞的细胞壁中存在硅。然而，硅仅特异性地定位于面向叶表面的周壁的外层，次生壁较厚，没有硅。免疫细胞化学实验用于确定硅沉积和聚糖聚合物的各自定位。果胶同质半乳糖醛酸和半纤维素木葡聚糖和甘露聚糖的特征表位在大多数表皮壁中被检测到，包括富含硅的细胞壁层。针对果胶阿拉伯聚糖的单克隆抗体 LM6 标记了表皮纤维状细胞的富含硅的初生壁和保卫细胞壁，这些细胞壁也被证明含有硅。我们假设表皮纤维状细胞的硅化外壁层在次生壁形成之前支持叶片的细胞扩张。这意味着硅化不会阻碍细胞伸长。虽然我们的结果表明果胶阿拉伯聚糖可能参与硅沉积，但需要进一步的详细分析来证实这一点。这里提出的组合方法允许对硅和细胞壁多糖分布进行相关筛选和原位定位，为未来的研究展示了巨大的潜力。
