Confocal Raman microscopy was used to illustrate changes of molecular composition in secondary plant cell wall tissues of poplar (Populus nigra × Populus deltoids) wood. Two-dimensional spectral maps were acquired and chemical images calculated by integrating the intensity of characteristic spectral bands. This enabled direct visualization of the spatial variation of the lignin content without any chemical treatment or staining of the cell wall. A small (0.5 μm) lignified border toward the lumen was observed in the gelatinous layer of poplar tension wood. The variable orientation of the cellulose was also characterized, leading to visualization of the S1 layer with dimensions smaller than 0.5 μm. Scanning Raman microscopy was thus shown to be a powerful, nondestructive tool for imaging changes in molecular cell wall organization with high spatial resolution.
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