Ectopic lignification in primary cellulose-deficient cell walls of maize cell suspension cultures

Abstract

Maize (Zea mays L.) suspension-cultured cells with up to 70% less celluloseQ1 were obtained by stepwise habituation to dichlobenil (DCB), a cellulose biosynthesis inhibitor. Cellulose deficiency was accompanied by marked changes in cell wall matrix polysaccharides and phenolics as revealed by Fourier transform infrared (FTIR) spectroscopy. Cell wall compositional analysis indicated that the cellulosedeficient cell walls showed an enhancement of highly branched and cross-linked arabinoxylans, as well as an increased content in ferulic acid, diferulates and pcoumaric acid, and the presence of a polymer that stained positive for phloroglucinol. In accordance with this, cellulosedeficient cell walls showed a fivefold increase in Klasontype lignin. Thioacidolysis/GC-MS analysis of cellulosedeficient cell walls indicated the presence of a ligninlike polymer with a Syringyl/Guaiacyl ratio of 1.45, which differed from the sensu stricto stress-related lignin that arose in response to short-term DCB-treatments. Gene expression analysis of these cells indicated an overexpression of genes specific for the biosynthesis of monolignol units of lignin. A study of stress signaling pathways revealed an overexpression of some of the jasmonate signaling pathway genes, which might trigger ectopic lignification in response to cell wall integrity disruptions. In summary, the structural plasticity of primary cell walls is proven, since a lignification process is possible in response to cellulose impoverishment