Heterogeneity of silica and glycan-epitope distribution in epidermal idioblast cell walls in Adiantum raddianum laminae
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ORIGINAL ARTICLE
Heterogeneity of silica and glycan-epitope distribution in epidermal idioblast cell walls in Adiantum raddianum laminae Olivier Leroux • Frederic Leroux • Alexandra Antunes Mastroberti • Fernanda Santos-Silva • Denis Van Loo • Agnieszka Bagniewska-Zadworna • Luc Van Hoorebeke • Sara Bals • Zoe¨ A. Popper • Jorge Ernesto de Araujo Mariath
Received: 29 November 2012 / Accepted: 1 February 2013 / Published online: 22 February 2013 Ó Springer-Verlag Berlin Heidelberg 2013
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.
O. Leroux Z. A. Popper Botany and Plant Science and the Ryan Institute for Environmental, Marine and Energy Research, School of Natural Sciences, National University of Ireland, Galway, University Road, Galway, Ireland
F. Santos-Silva Instituto de Pesquisas Jardim Botaˆnico do Rio de Janeiro, Rua Pacheco Lea˜o 2040, Rio de Janeiro 22460-030, Brazil
O. Leroux Pteridology, Department of Biology, Ghent University, K.L. Ledeganckstraat 35, B-9000 Ghent, Belgium F. Leroux S. Bals Department of Physics, EMAT, University of Antwerp, Groenenborgerlaan 171, BE-2020 Antwerpen, Belgium A. A. Mastroberti (&) F. Santos-Silva J. E. de Araujo Mariath Laboratory of Plant Anatomy, Department of Botany, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil e-mail: alexandra.mastroberti@u
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