Imaging Lignin-Downregulated Alfalfa Using Coherent Anti-Stokes Raman Scattering Microscopy

Targeted lignin modification in bioenergy crops could potentially improve conversion efficiency of lignocellulosic biomass to biofuels. To better assess the impact of lignin modification on overall cell wall structure, wild-type and lignin-downregulated alfalfa lines were imaged using coherent anti-Stokes Raman scattering (CARS) microscopy. The 1,600-cm ^-1 Raman mode was used in CARS imaging to specifically represent the lignin signal in the plant cell walls. The intensities of the CARS signal follow the general trend of lignin contents in cell walls from both wild-type and lignin-downregulated plants. In the downregulated lines, the overall reduction of lignin content agreed with the previously reported chemical composition. However, greater reduction of lignin content in cell corners was observed by CARS imaging, which could account for the enhanced susceptibility to chemical and enzymatic hydrolysis observed previously.