Zexer Nerya, Elbaum Rivka
The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, The Hebrew University of Jerusalem, Rehovot, Israel.
J Exp Bot. 2020 Dec 2;71(21):6818-6829. doi: 10.1093/jxb/eraa127.
Silicon dioxide in the form of hydrated silica is a component of plant tissues that can constitute several percent by dry weight in certain taxa. Nonetheless, the mechanism of plant silica formation is mostly unknown. Silicon (Si) is taken up from the soil by roots in the form of monosilicic acid molecules. The silicic acid is carried in the xylem and subsequently polymerizes in target sites to silica. In roots of sorghum (Sorghum bicolor), silica aggregates form in an orderly pattern along the inner tangential cell walls of endodermis cells. Using Raman microspectroscopy, autofluorescence, and scanning electron microscopy, we investigated the structure and composition of developing aggregates in roots of sorghum seedlings. Putative silica aggregation loci were identified in roots grown under Si starvation. These micrometer-scale spots were constructed of tightly packed modified lignin, and nucleated trace concentrations of silicic acid. Substantial variation in cell wall autofluorescence between Si+ and Si- roots demonstrated the impact of Si on cell wall chemistry. We propose that in Si- roots, the modified lignin cross-linked into the cell wall and lost its ability to nucleate silica. In Si+ roots, silica polymerized on the modified lignin and altered its structure. Our work demonstrates a high degree of control over lignin and silica deposition in cell walls.
水合二氧化硅形式的二氧化硅是植物组织的一种成分，在某些分类群中按干重计算可占百分之几。尽管如此，植物硅形成的机制大多仍不为人知。硅（Si）以单硅酸分子的形式被根从土壤中吸收。硅酸在木质部中运输，随后在目标部位聚合成二氧化硅。在高粱（Sorghum bicolor）的根中，二氧化硅聚集体沿着内皮层细胞的内切向细胞壁以有序的模式形成。利用拉曼显微光谱、自发荧光和扫描电子显微镜，我们研究了高粱幼苗根中正在形成的聚集体的结构和组成。在硅饥饿条件下生长的根中鉴定出了假定的硅聚集体位点。这些微米级的斑点由紧密堆积的改性木质素构成，并使痕量浓度的硅酸成核。硅充足和硅缺乏的根之间细胞壁自发荧光的显著差异表明了硅对细胞壁化学的影响。我们提出，在硅缺乏的根中，改性木质素交联到细胞壁中并失去了使硅成核的能力。在硅充足的根中，二氧化硅在改性木质素上聚合并改变了其结构。我们的工作表明对细胞壁中木质素和硅的沉积有高度的控制。
