ABSTRACT
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Lignin is a chemically recalcitrant polymer of phenylpropanoid units linked together in a complex and irregular pattern which varies from species to species, tissue to tissue, and cell to cell. Vascular plants use lignin to line their conductive vascular tissues as a barrier to water loss; thus, lignin has been instrumental in the spread of these plants throughout the terrestrial landscape. Plants have subsequently harnessed lignin to bind cells together, rigidify their lamellate cell walls into fantastically strong microcomposites, and provide a physical barrier to invading microorganisms. Because lignin plays such a variety of critical roles in plant biology, numerous techniques have been developed for its quantitation and qualitative analysis. However, any researcher embarking on a study of lignin should understand from the outset that there are as yet no absolutes in lignin analysis. Each of the techniques discussed in the following sections has significant limitations, and as a consequence, this chapter has been prepared so as to highlight potential sources of error and artifact. This being said, rapid advances in spectroscopic analysis, particularly techniques that may be applied to lignocellulosic materials in situ, promise to make the quantitation and characterization of lignin both rapid and routine, as well as more accurate. Such techniques are becoming increasingly critical as our ability to use biochemistry, molecular biology, and computer modeling to probe lignin structure and biosynthesis outstrips the capacity of older lignin analysis techniques to provide detailed information about this important biopolymer.
