Around 10 years ago the coupling of Raman spectroscopy with Confocal microscopy evolved as a powerful imaging tool to get insights into cell wall chemistry and structure of the native wooden cell walls with submicron resolution1,2. Two-dimensional spectral maps can be acquired and chemical images calculated by integrating the intensity of characteristic spectral bands or by using multivariate data analysis methods3. The variability of cell wall composition is revealed, including changes in the orientation of the cellulose microfibrils4 as well as the spatial variation of lignin amount and composition in context with the cell structure5. Due to the multicomponent nature of plant cell walls the Raman spectra usually comprise overlapping bands from cellulose, hemicellulose, lignin and extractives. Therefore especially multivariate approaches aiming in unmixing the multicomponent spectra, like vertex component analysis (VCA) and non negative matrix factorization (NMF) have potential to reveal new insights6. VCA revealed that the lumen sided S3 layer as well as the pits, functioning as connection valves between the water contucting tracheids, have a different lignin composition than the main part of the secondary cell wall-layer (S2)5. During heartwood formation of pine an additional hydrophobisation has been observed by impregnation with stilbenes in a similar pattern with accumulations in the S3 and pits (Fig.1) The different lignin composition and extractive impregnation of the surface layers and connection pathways is of relevance for plant cell wall processing as well as resistance against abiotic and biotic stresses and decay.

Following in-situ hydrophobisation of plant cell walls by Raman imaging

253rd National Meeting (2017)

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