In situ imaging of lignin and related compounds by Raman, Fourier-transform infrared (FTIR) and fluorescence microscopy

Spectral imaging technologies simultaneously record spectral and spatial information about plant tissues in a noninvasive way. Differences in techniques result in different selection rules and spatial resolutions. This article introduces the basic principles of Raman, Fourier-transform Infrared (FTIR) and autofluorescence imaging and finally compares their strength and drawbacks. The methods result in spectral datasets as bases for image generation. Spectral preprocessing together with univariate and multivariate data analysis approaches are essential for informative lignin imaging and analysis and therefore also briefly illustrated and discussed. Examples of imaging lignin and other aromatic components in a broad range of plant tissues show the potential as well as the limitations of microspectroscopic imaging.