Nanoscale FTIR and Mechanical Mapping of Plant Cell Walls for Understanding Biomass Deconstruction

Nano-FTIR and PeakForce quantitative nanomechanical mapping (PF QNM) are new AFM-based techniques that can be applied to plant tissues to get high-resolution spatial distribution of features that are unavailable from bulk characterization. This can be useful for finding changes to plant cell walls by processing technologies, mutations, or the environment. Three poplar hardwoods of varying recalcitrance and composition (high lignin, low lignin, and mutant) were investigated by nano-FTIR and PF QNM. Bulk characterization was carried out by conventional FTIR and NMR of isolated cellulose, hemicelluloses, and lignin. We found that in nano-FTIR spectra of secondary cell walls (SCW) and compound middle lamella (CML), 1162 and 1269 cm(-1) could distinctly identify polysaccharides and lignin, respectively. Spatial variability in the content of polysaccharides and lignin was significantly larger in CML than SCW for all three poplars. Cellulose has a disordered structure in CML in comparison to SCW. PF QNM showed that SCW had a higher modulus of elasticity than CML due to the presence of crystalline cellulose in SCW. Differences in the physicochemical properties between the SCW and CML of plants can be probed at nanoscale by these techniques.