Reassessment of qualitative changes in lignification of transgenic tobaccoplants and their impact on cell wall assembly

In tobacco plants the effect of antisense down-regulation of various genes encoding enzymes of the monolignol biosynthetic pathway resulted in quantit ative and qualitative changes in lignin distribution and in diverse alterat ions of the secondary wall assembly of modified tobacco plants. Total ligni n content, composition in syringyl and guaiacyl units, and absolute proport ions of condensed and non-condensed substructures occurring in the cell wal ls, were differentially modified according to the repressed gene. Immunocyt ochemical characterisation and visualisation of the distribution of condens ed and non-condensed lignin substructure epitopes in transmission electron microscopy (TEM) revealed that some transformations entailed profound and s pecific alterations in the secondary wall biogenesis. Correlation between m icro-morphological cell wall alterations and semi-quantitative immunoanalys is of the topochemical distribution of lignin sub-units suggests that the m ode of polymerisation of monolignols into non-condensed units, favoured by the microfibril matrix of the secondary wall, plays an important part in th e lignified cell wall assembly. (C) 2001 Elsevier Science Ltd. All rights r eserved.