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ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Research » Publications at this Location » Publication #97018
Title: DETECTION AND DETERMINATION OF P-COUMAROYLATED UNITS IN LIGNINS

Author
item LU, FACHUANG - UNIV OF WISCONSIN-MADISON
item Ralph, John

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: A major component in all terrestrial plants, lignin is a polymer that limits digestion of plants by animals and must be removed from wood to make paper. We recently developed a new analytical method, the "DFRC" method (for Derivatization Followed by Reductive Cleavage, but also identifying the Dairy Forage Research Center where it was developed) that cleanly degrades lignins to simple analyzable compounds that give insight into the structural details of the original lignin. Such methods provide scientists with enhanced research tools. All grasses have so-called p-coumarates in their lignins. Their function appears to range from being a facilitator in the production of the large lignin polymers to defense roles. Currently there is no simple way of finding out how the p-coumarates are attached to lignin and on what types of lignin units they occur. Since the DFRC method leaves these units essentially intact while breaking up the lignin structure around it, we can release for analysis lignin fragments with p- coumarate attached. Analysis of these fragments provides insight into the basic processes occurring during growth and development of grasses. These wide-ranging studies ultimately are aimed at improving agricultural sustainability and maximizing our plant resources.

Technical Abstract: The DFRC (Derivatization Followed by Reductive Cleavage) method cleaves alpha- and beta-ethers in lignins but leaves lignin gamma-esters intact. When applied to grasses, which contain p-coumarate esters on their lignins, esterified monolignol derivatives are released. Saturation of the p- coumarate double-bond occurs during DFRC, so the released products are 4- acetoxycinnamyl 4-acetoxyphenylpropionates. Synthesis of the esters allowe determination of response factors for the released products. Maize and bamboo lignins released 221 and 38 mmoles/g of p-coumarate-derived esters. The sinapyl ester was much more abundant than the coniferyl one. The bamboo and maize lignin S/G ratios in the conjugates were 12- and 38-times greater than those of the normal monomers released by DFRC, evidence of a strong selectivity for acylation of syringyl units. Of three possible biochemical mechanisms for incorporating p-coumarates into lignin, evidence is mounting gthat the process involves incorporation of pre-acylated monolignols into the normal lignification process.