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. 1997 Sep;115(1):41–50. doi: 10.1104/pp.115.1.41

Reduced Lignin Content and Altered Lignin Composition in Transgenic Tobacco Down-Regulated in Expression of L-Phenylalanine Ammonia-Lyase or Cinnamate 4-Hydroxylase.

VJH Sewalt 1, W Ni 1, J W Blount 1, H G Jung 1, S A Masoud 1, P A Howles 1, C Lamb 1, R A Dixon 1
PMCID: PMC158458  PMID: 12223790

Abstract

We analyzed lignin content and composition in transgenic tobacco (Nicotiana tabacum) lines altered in the expression of the early phenylpropanoid biosynthetic enzymes L-phenylalanine ammonia-lyase and cinnamate 4-hydroxylase (C4H). The reduction of C4H activity by antisense expression or sense suppression resulted in reduced levels of Klason lignin, accompanied by a decreased syringyl/guaiacyl monomer ratio as determined by pyrolysis gas chromatography/mass spectrometry Similar reduction of lignin levels by down -regulation of L-phenylalanine ammonia-lyase, the enzyme preceding C4H in the central phenylpropanoid pathway, did not result in a decreased syringyl/guaiacyl ratio. Rather, analysis of lignin methoxyl content and pyrolysis suggested an increased syringyl/guaiacyl ratio. One possible explanation of these results is that monolignol biosynthesis from L-phenylalanine might occur by more than one route, even at the early stages of the core phenylpropanoid pathway, prior to the formation of specific monolignol precursors.

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Selected References

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