Insight into the structural organization of the cell wall polymers in compression wood using synchrotron FTIR microspectroscopy

Compression wood (CW) serves as an ideal model for studying cell wall polymer assembly under mechanical stress, yet its spatial heterogeneity challenges detailed structural characterization. In this study, we employed polarized synchrotron Fourier-transform infrared (S-FTIR) microspectroscopy and high-resolution S-FTIR mapping (pixel size of 5 × 5 µm) to investigate the molecular orientation and distribution of cellulose, lignin, and hemicellulose subfractions in radial and tangential walls of Chinese fir CW. Polarized spectra revealed that cellulose C–O–C bonds are partially ordered in radial walls (molecular order parameter = 0.50 ± 0.04 at 1160 cm⁻¹), whereas lignin and hemicellulose show negligible orientation. The similar distributions of lignin (1508 cm⁻¹) and arabinose (1312 cm⁻¹) observed in S‑FTIR imaging results suggested that arabinose‑containing hemicellulose is probably directly linked to lignin via benzyl ether bonds in CW. The deconvolution and semi-quantitative analysis of peak‑area ratios (A polymer /A 1508 ) demonstrated that galacturonic acid monohydrate, galactomannan, and xylose‑containing hemicellulose are significantly more abundant in radial walls, whereas arabinose and mannose‑containing hemicellulose display comparable abundances in radial and tangential walls. These findings demonstrate the remarkable capabilities of high-resolution S-FTIR microspectroscopy for in situ analysis of the intricate architecture of plant cell walls and provide insights for understanding the biomechanics and biosynthesis of plants under external stimuli.