title: The cell biology of lignification in higher plants.
abstract: BACKGROUND
  Lignin is a polyphenolic polymer that strengthens and waterproofs the cell wall of specialized plant cell types. Lignification is part of the normal differentiation programme and functioning of specific cell types, but can also be triggered as a response to various biotic and abiotic stresses in cells that would not otherwise be lignifying.
  
  
  METHODS
  Cell wall lignification exhibits specific characteristics depending on the cell type being considered. These characteristics include the timing of lignification during cell differentiation, the palette of associated enzymes and substrates, the sub-cellular deposition sites, the monomeric composition and the cellular autonomy for lignin monomer production. This review provides an overview of the current understanding of lignin biosynthesis and polymerization at the cell biology level.
  
  
  CONCLUSIONS
  The lignification process ranges from full autonomy to complete co-operation depending on the cell type. The different roles of lignin for the function of each specific plant cell type are clearly illustrated by the multiple phenotypic defects exhibited by knock-out mutants in lignin synthesis, which may explain why no general mechanism for lignification has yet been defined. The range of phenotypic effects observed include altered xylem sap transport, loss of mechanical support, reduced seed protection and dispersion, and/or increased pest and disease susceptibility.
authors: Umeå Plant Science Centre (UPSC), Department of Plant Physiology, Umeå University, 901 87 Umeå, Sweden.
authors: Jaime
authors: J
authors: Barros
authors: Umeå Plant Science Centre (UPSC), Department of Plant Physiology, Umeå University, 901 87 Umeå, Sweden.
authors: Henrik
authors: H
authors: Serk
authors: Umeå Plant Science Centre (UPSC), Department of Plant Physiology, Umeå University, 901 87 Umeå, Sweden.
authors: Irene
authors: I
authors: Granlund
authors: Umeå Plant Science Centre (UPSC), Department of Plant Physiology, Umeå University, 901 87 Umeå, Sweden Edouard.pesquet@umu.se.
authors: Edouard
authors: E
authors: Pesquet
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D002473:Cell Wall / Q000378:metabolism; D019669:Embryophyta / Q000235:genetics* / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D008031:Lignin / Q000378:metabolism*
chemical_list: D008031:Lignin
keywords: Arabidopsis thaliana; Lignin; laccases; lignification; monolignols; non-cell autonomous processes; peroxidases; plant cell wall