To characterize the structures of intact lignin in plant cell walls, an effective method based on mild alkaline pretreatment and enzymatic hydrolysis was applied to isolate residual enzyme lignin (REL). The REL obtained was investigated as compared to the corresponding cellulolytic enzyme lignin (CEL). The yield of REL (95-98%) was significantly higher than that of corresponding CEL (19-23%). In addition, the associated carbohydrates were observed in REL (8.1-13.2%) and CEL (4.6-7.2%). The lignins obtained have been comparatively investigated by a combination of 2D-HSQC NMR, 31P-NMR, analytical pyrolysis, and GPC techniques. The major lignin substructures in these lignin samples, such as �-O-4, �-�, and �-5, can be assigned and the frequencies of the major lignin linkages were quantitatively obtained. Interestingly, the ?-acylated p-hydroxybenzoate (PB) esters were also detected and the PB levels (relative to total lignin G+S units) were significantly elevated in the C3H down-regulated transgenic poplars. The elevation of the PB was accompanied by relative depletion of G units, as revealed by the slightly increased S/G ratios. In particular, p-hydroxyphenyl (H) units were observed in REL rather than CEL. Considering the higher S/G ratio of CEL than corresponding REL, it was possible to conclude that H units are deposited at the earlier stages, which are difficult to be extracted with traditional methods (CEL), could be obtained by this method, while the lignin are enriched in syringyl (S) lignin during late lignifications, could be isolated as CEL. Inspiringly, the effective method gives us an integrated vision to understand the intrinsic structural features of lignin in plant cell wall.

Structural elucidation of native lignin from C<sub>3</sub>H down-regulated transgenic poplars based on preswollen and enzymatic hydrolysis

247th National Meeting (2014)

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Structural elucidation of native lignin from C3H down-regulated transgenic poplars based on preswollen and enzymatic hydrolysis

Structural elucidation of native lignin from C₃H down-regulated transgenic poplars based on preswollen and enzymatic hydrolysis