Vibrational fingerprint mapping reveals spatial distribution of functional groups of lignin in plant cell wall.

Highly lignified vascular plant cell walls represent the majority of cellulosic biomass. Complete release of the biomass to deliver renewable energy by physical, chemical, and biological pretreatments is challenging due to the "protection" provided by polymerized lignin, and as such, additional tools to monitor lignin deposition and removal during plant growth and biomass deconstruction would be of great value. We developed a hyperspectral stimulated Raman scattering microscope with 9 cm(-1) spectral resolution and submicrometer spatial resolution. Using this platform, we mapped the aromatic ring of lignin, aldehyde, and alcohol groups in lignified plant cell walls. By multivariate curve resolution of the hyperspectral images, we uncovered a spatially distinct distribution of aldehyde and alcohol groups in the thickened secondary cell wall. These results collectively contribute to a deeper understanding of lignin chemical composition in the plant cell wall.