In herbaceous biomasses lignin and hydroxycinnamic acids (ferulic acid and cinnamic acid) content is an important influence on recalcitrance, which limits enzyme infiltration into cell walls. The confocal Raman microscopy was used to topochemically detect lignin and hydroxycinnamic acids in sclerenchymatous fiber (Sf), protoxylem vessel (Pxv), metaxylem vessel (Mxv) and parenchyma (Par) cell walls of untreated and sodium borohydride treated vascular bundles in Miscanthus sinensis. Raman images obtained by integration over the Raman band at 1604 cm-1 of both samples clearly showed that the secondary wall of Mxv had the highest level of lignification, followed by Sf and Pxv secondary wall and the lowest in the Par secondary wall. Within the individual cell wall of Sf, cell corner middle lamella (CCML) was more lignified than adjacent compound middle lamella (CML) and secondary wall with variation in lignification level from cell to cell. Model compounds analysis revealed that the Raman band at 1628 cm-1 and 1168 cm-1 were mainly derived from the hydroxycinnamic acids, which was further confirmed by reduction reaction with the sodium borohydride. Integrating over the band ranges from 1170-1160 cm-1 identified the pattern of hydroxycinnamic acids distribution with the highest concentration occurring in the CML and secondary wall of Sf and Par. However, in Pxv lower intensity was visualized in the secondary wall where there was the high lignin concentration. The information on topochemical distribution of lignin and hydroxycinnamic acids will deepen our understanding of the natural biomass recalcitrance.

Topochemical distribution of lignin and hydroxycinnamic acids in Miscanthus sinensis cell walls

245th National Meeting (2013)

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