Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/13/2008
Publication Date: 8/25/2008
Citation: Ralph, J., Kim, H., Lu, F., Grabber, J.H., Boerjan, W., Lapierre, C. 2008. Identification of the structure and origin of a thioacidolysis marker compound for ferulic acid incorporation into angiosperm lignins (and an indicator for cinnamoyl-CoA reductase deficiency). In: Ferulate 08 Abstracts, August 25-27, 2008, Minneapolis, Minnesota. p. 25.
Technical Abstract: A molecular marker compound, derived from lignin by the thioacidolysis degradative method, for structures produced when ferulic acid is incorporated into lignification in angiosperms (poplar, Arabidopsis, tobacco), has been structurally identified as 1,2,2-trithioethyl ethylguaiacol [1-(4-hydroxy-3-methoxyphenyl)-1,2,2-tris(ethylthio)ethane]. Its truncated sidechain and distinctive oxidation state suggest it derives from ferulic acid that has undergone bis-8–O–4-(cross-)coupling during lignification, as validated by model studies. A diagnostic contour for such structures is found in 2D 13C–1H correlated (HSQC) nuclear magnetic resonance (NMR) spectra of lignins isolated from poplar deficient in cinnamoyl-CoA reductase (CCR). As low levels of the marker are also released from normal (i.e. non-transgenic) plants in which ferulic acid may be present during lignification, notably in grasses, we term this only an indicator for CCR-deficiency in general, but a reliable marker in woody angiosperms such as poplar. Its derivation, along with evidence for 4-O-etherified ferulic acid, strongly implies that ferulic acid incorporates into angiosperm lignins. Its endwise radical coupling reactions suggest that ferulic acid should be considered an authentic lignin precursor. Moreover, ferulic acid incorporation provides a new mechanism for producing branch-points in the polymer. The findings sharply contradict those reported in a recent study on CCR-deficient Arabidopsis.