Submitted to: International Symposium on Wood and Pulping Chemistry
Publication Type: Proceedings
Publication Acceptance Date: 12/9/1998
Publication Date: N/A
Technical Abstract: The lignins in a number of mutant and transgenic plants, deficient in monolignol biosynthetic enzymes 4CL, F5H, CCR, and CAD, have been examined by NMR and degradative methods. These plants provide significant insights into lignification processes. In some cases the lignin content and composition have been altered, while in others the lignin content, as measured by traditional means, has not appreciably declined but the lignin structure is changed, sometimes dramatically. Phenolic components not normally associated with lignification appear to be incorporated into the lignin polymer of some deficient plants. Although there remain some issues regarding the location and function of these components and their classification as lignins, in terms of plant utilization (e.g. by pulping), these phenolics contribute to the polymeric class generically referred to as "lignins" and must be processed accordingly. NMR provides rich structural detail but only on soluble components which represent a fractio of the total lignin. Methods to render the entire lignin suitable for NMR study, along with traditional and new degradative methods, are providing further evidence that the lignins in some mutants/transgenics are indeed significantly derived from components other than the traditional three monolignols. This metabolic plasticity means that attempts to down-regulate lignification by targeting pathway enzymes may not always be successful (because plants may make as much "lignin" from other phenolics), but provides significant opportunities to engineer the properties of lignins to allow more extensive "exploitation" of plant resources.