[Confocal Raman microspectroscopy study on the distribution of cellulose and lignin in Daphne odora Thunb]

Confocal Raman microspectroscopy is well suited to investigating cellulose and lignin distribution in-situ in the native cell walls of woody tissue. In this study, transmission electron microscopy (TEM) was used to determine the ultrastructure of Daphne odora Thunb. In the TEM images, cell wall of Daphne odora Thunb. is typically divided into three layers: middle lamellar (ML), primary wall (P) and secondary wall (S1, S2 and S3). More detailed information about cellulose and lignin distribution in different cell wall layers was analyzed in situ by confocal Raman microspectroscopy. Raman spectra and images reveal that the distribution of cellulose and lignin in the cell wall layers is not uniform. Lignin concentration in different morphological areas follows the decreasing order: the cell corner (CC) > the middle lamellar (CML) > the secondary wall (S2). In contrast, cellulose distribution shows the opposite pattern-low concentration in CC and CML and high in S2 regions.