Heterogeneity of silica and glycan-epitope distribution in epidermal idioblast cell walls in Adiantum raddianum laminae

Abstract

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.

A possible mechanism of biological silicification in plants

“…By way of an example, the differentiation of stomata is a complex process in which callose is involved in almost every step. Apostolakos et al (2009 , 2010 ) have detailed these stages in fern ( Asplenium nidus L.), a known silica accumulator ( Leroux et al, 2013 ) and we have shown that silica deposition exactly mimics callose deposition in horsetail ( Law and Exley, 2011 ) and in fern ( Figure 2 ). These observations not only support a specific role for callose in silica deposition they demonstrate that the deposition of silica in plants is not simply a one-way process but must involve the modeling, dissolution, and remodeling of silica structures.…”

“…There are structures which appear more heavily silicified than others and their propensities for silicification are probably determined by the respective densities of the molecular structures acting as templates of the precipitation process. We have identified the hemicellulose callose as one such molecular template for biological silicification ( Law and Exley, 2011 ) and others will probably include precursors to and components of plant cell walls ( Fleck et al, 2011 ; Fernández Honaine and Osterrieth, 2012 ; Yamanaka et al, 2012 ; Fernández Honaine et al, 2013 ; Leroux et al, 2013 ; Zhang et al, 2013 ).…”

Silica distinctively affects cell wall features and lignocellulosic saccharification with large enhancement on biomass production in rice

“…Silica is the final and most prevailing form of silicon deposit in plants [24][25][26][27], and is an important factor on wall-network formation in plant cell walls [28][29][30]. In addition, high silica content in rice straw has been considered as a negative factor on biomass digestibility http://dx.doi.org/10.1016/j.plantsci.2015.07.014 0168-9452/© 2015 Elsevier Ireland Ltd. All rights reserved.…”

<I>Adiantum alan-smithii</I> (Pteridaceae), a New Maidenhair Fern from Chiapas, Mexico

“…Adiantoids comprise Adiantum and their sister group, the vittarioid ferns (Prado et al 2007;Schuettpelz et al 2007). The sister relationship of these two groups is further supported by the shared morphological features of reddish young leaves (Sundue 2011) and silicified, epidermal, fiberlike cells, often referred to as venuloid idioblasts or silica bodies (Sundue 2009;Leroux et al 2013).…”

“…Sundue (2009) demonstrated that they are probably present in all Adiantum, but inconspicuous except in cases when they occur between veins, such as in the A. tetraphyllum group. Kao et al (2008) and Sundue (2009) determined these cells were silicified using x-ray scanning electron microscopy (SEM) and wet-ashing, respectively, and referred to them as silica bodies; however, Leroux et al (2013) demonstrated that the silica was confined to the cell wall and not the lumen, and so suggested the name 'silicified fiber-like cells', which we adopt here.…”