Reduced Lignin Content and Altered Lignin Composition in Transgenic Tobacco Down-Regulated in Expression of L-Phenylalanine Ammonia-Lyase or Cinnamate 4-Hydroxylase.
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.
Sewalt
VJH.
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Plant Biology Division, Samuel Roberts Noble Foundation, P.O. Box 2180, Ardmore, Oklahoma 73402 (V.J.H.S., J.W.B., P.A.H., S.A.M., R.A.D.).
Ni
W.
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Blount
J. W.
JW
Jung
H. G.
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Masoud
S. A.
SA
Howles
P. A.
PA
Lamb
C.
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Dixon
R. A.
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