Submitted to: Journal of the Chemical Society Perkin Transactions 1
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2001
Publication Date: N/A
Citation: Interpretive Summary: Mutant and transgenic plants provide useful insights into the biochemical processes occurring in normal plants. It has recently been found that plants will change the makeup and structure of their lignin (the polymer that holds fibers together in woody and forage plants) if they are not able to produce lignins normally. When enzymes late in the lignin pathway (including COMT described here) are deficient, the plants use components that they can make by normal processes as novel precursors for their modified lignins. This study extends the preliminary finddings reported in a previous paper, detailing the structural changes in lignin that result from COMT-deficiency. It is also the first application of a 3-dimensional NMR technique to natural lignins that have not been isotopically labeled. It is becoming increasingly evident that plants are able to incorporate substantial amounts of components that are not normally considered to be precursors of lignins. This means that breeding or biogenetic engineering can be used to enhance these components if they are found to be of value. Such studies are at the heart of efforts to improve the utilization of valuable plant resources in processes ranging from digestion of forages by ruminants to industrial paper production by chemical pulping.
Technical Abstract: Perturbing the lignin biosynthetic pathway provides a tool for understanding the complex process of lignification. Caffeic acid O-methyltransferase (COMT) is required to produce syringyl units in lignins. Downregulating its gene in poplar dramatically affects the lignin composition. 2D and 3D NMR investigations detail structural differences between lignins from a control and COMT-deficient poplars obtained by mean of two independent transformation techniques. This first application of 3D NMR to natural abundance lignins reveals the full sidechain network and provides diagnostic evidence for the intimate incorporation of 5-hydroxyconiferyl alcohol into the lignins to form novel benzodioxanes as major structures. The flexibility of a plant to utilize novel monomers to produce functional lignins provides opportunities for engineering the structure and affecting the consequent properties of lignins.