Ultrastructure and composition of cell wall appositions in the roots of Asplenium (Polypodiales)

• Published in: Micron (Oxford, England : 1993) England : 1993), 2011-12, Vol.42 (8), p.863-870
• Main Authors: Leroux, O., Leroux, F., Bagniewska-Zadworna, A., Knox, J.P., Claeys, M., Bals, S., Viane, R.L.L.
• Format: Article
• Language: English
• Subjects: Apposition; Asplenium; callose; Cell Wall - chemistry; Cell Wall - ultrastructure; cell wall components; Cell walls; cellulose; Electron microscopy; Ferns; Ferns - chemistry; Ferns - microbiology; Ferns - ultrastructure; ferns and fern allies; Fluorescent Antibody Technique; fungi; Fungi - pathogenicity; Histology; Host-Pathogen Interactions; lignin; Microscopy; monoclonal antibodies; phenolic compounds; pigments; Plant Roots - chemistry; Plant Roots - microbiology; Plant Roots - ultrastructure; Plant–microbe-interaction; roots; Staining and Labeling - methods; transmission electron microscopy; ultrastructure; warts; xyloglucans
• ISSN: 0968-4328; 1878-4291
• DOI: 10.1016/j.micron.2011.06.002

► Cell wall appositions appear at the contact site with micro-organisms in fern roots. ► Infecting microbes are immobilized when attempting to penetrate intracellularly. ► Cell wall appositions are made of a non-lignified polysaccharide matrix. ► Callose and lignins are absent, yellow-brown phenolic compounds are present. ► They create a barrier protecting the root against infections. Cell wall appositions (CWAs), formed by the deposition of extra wall material at the contact site with microbial organisms, are an integral part of the response of plants to microbial challenge. Detailed histological studies of CWAs in fern roots do not exist. Using light and electron microscopy we examined the (ultra)structure of CWAs in the outer layers of roots of Asplenium species. All cell walls studded with CWAs were impregnated with yellow-brown pigments. CWAs had different shapes, ranging from warts to elongated branched structures, as observed with scanning and transmission electron microscopy. Ultrastructural study further showed that infecting fungi grow intramurally and that they are immobilized by CWAs when attempting to penetrate intracellularly. Immunolabelling experiments using monoclonal antibodies indicated pectic homogalacturonan, xyloglucan, mannan and cellulose in the CWAs, but tests for lignins and callose were negative. We conclude that these appositions are defense-related structures made of a non-lignified polysaccharide matrix on which phenolic compounds are deposited in order to create a barrier protecting the root against infections.