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Article on the effects of coumarate 3-hydroxylase down-regulation on lignin structure.
Physical Description
11 p.
Notes
Abstract: Down-regulation of the gene encoding 4-coumarate 3-hydroxylase (C3H) in alfalfa massively but predictably increased the proportion of p-hydroxyphenyl (P) units relative to the normally dominant guaiacyl (G) and syringyl (S) units. Stem levels of up to ∼65% P (from wild-type levels of ∼1%) resulting from down-regulation of C3H were measured by traditional degradative analyses as well as two-dimensional13C-1H correlative NMR methods. Such levels put these transgenics well beyond the P:G:S compositional bounds of normal plants; p-hydroxyphenyl levels are reported to reach a maximum of 30% in gymnosperm severe compression wood zones but are limited to a few percent in dicots. NMR also revealed structural differences in the interunit linkage distribution that characterizes a lignin polymer. Lower levels of key β-aryl ether units were relatively augmented by higher levels of phenylcoumarans and resinols. The C3H-deficient alfalfa lignins were devoid of β-1 coupling products, highlighting the significant differences in the reaction course for p-coumaryl alcohol versus the two normally dominant monolignols, coniferyl and sinapyl alcohols. A larger range of dibenzodioxocin structures was evident in conjunction with an approximate doubling of their proportion. The nature of each of the structural units was revealed by long range13C-1H correlation experiments. For example, although β-ethers resulted from the coupling of all three monolignols with the growing polymer, phenylcoumarans were formed almost solely from coupling reactions involving p-coumaryl alcohol; they resulted from both coniferyl and sinapyl alcohol in the wild-type plants. Such structural differences form a basis for explaining differences in digestibility and pulping performance of C3H-deficient plants.
Publication Title:
Journal of Biological Chemistry
Volume:
281
Issue:
13
Page Start:
8843
Page End:
8853
Peer Reviewed:
Yes
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Ralph, John; Akiyama, Takuya; Kim, Hoon; Lu, Fachuang; Schatz, Paul F.; Marita, Jane M. et al.Effects of Coumarate 3-Hydroxylase Down-regulation on Lignin Structure,
article,
March 31, 2006;
[Rockville, Maryland].
(https://digital.library.unt.edu/ark:/67531/metadc488185/:
accessed March 19, 2024),
University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu;
crediting UNT College of Arts and Sciences.