Improving sample preparation to investigate lignin intensity of xylem at the cellular level by confocal Raman microspectroscopy of Populus tomentosa

Confocal Raman microspectroscopy (CRM) is an important tool for analyzing the compositional distribution of cell walls in situ. In this study, we improved the sample preparation method using paraffin-embedded sections combined with hexane dewaxing to obtain high resolution Raman images. We determined that the cell wall components of fiber cells were different from those of ray cells and vessel cells in the xylem of Populus tomentosa . Acetyl bromide and CRM methods produced similar trends when the difference in lignin intensity in the xylem region was compared between transgenic PtrLac4 and wild-type P. tomentosa . However, CRM proved more useful to analyze the lignin distribution in each cell type and distinguished the detailed difference in lignin intensity at the cellular level. Thus, CRM proved to be a useful in situ method to rapidly analyze the spatial variation of lignin content in the xylem of woody plants.