Uniform elementary fibrils in diverse plant cell walls

Area of Science:

• Plant Biology
• Biophysics
• Materials Science

Background:

• Plant cell walls are primarily composed of cellulose microfibrils, hemicelluloses, and lignin.
• Cellulose microfibrils form a dense, skeletal network crucial for plant cell structure.
• Previous research indicated structural diversity in plant microfibrils across different species.

Purpose of the Study:

• To investigate the morphology and crystallinity of individually dispersed microfibrils from wood, cotton, and ramie.
• To compare microfibril structures across these distinct plant sources.
• To evaluate the consistency of microfibril dimensions and crystallinity.

Main Methods:

• Isolation and dispersion of microfibrils from wood, cotton, and ramie.
• Structural analysis using atomic force microscopy (AFM).
• Crystallinity assessment via wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS).
• Solid-state 13C NMR spectroscopy.
• All-atom molecular dynamics (MD) simulations.

Main Results:

• Dispersed microfibrils exhibited uniform cross-sectional dimensions (approx. 2-3 nm width) regardless of plant origin.
• Crystallite size (approx. 2 nm) and crystallinity degree (approx. 20%) were consistent across samples.
• Molecular dynamics simulations supported these findings, modeling microfibrils with 18 cellulose molecules.
• Bundling of 2-3 microfibrils was observed, stabilized by crystallite fusion.

Conclusions:

• Plant cellulose microfibrils display remarkable uniformity in dimensions and crystallinity, challenging previous notions of diversity.
• The findings support the biophysical hypothesis of cellulose biosynthesis involving a terminal complex (TC) of 18 synthases.
• Microfibril bundling is a common phenomenon, stabilized by crystallite fusion.