Atomic force microscopy of microfibrils in primary cell walls

Area of Science:

• Plant Biology
• Biophysics
• Materials Science

Background:

• Angiosperm primary cell walls comprise cellulose microfibrils embedded in non-cellulosic polysaccharides.
• Previous studies indicated cellulose crystallites of 2-3 nm, but microfibril dimensions remained debated.
• The number of crystallites per microfibril is unknown due to uncertainty in microfibril dimensions.

Purpose of the Study:

• To determine the precise dimensions of primary cell wall microfibrils in angiosperms.
• To investigate the relationship between microfibril dimensions and cellulose crystallite number.
• To clarify the structural organization of cellulose within plant cell walls.

Main Methods:

• Isolation and partial hydration of primary cell walls from *Allium cepa* (onion) and *Arabidopsis thaliana*.
• Atomic force microscopy (AFM) was employed to measure microfibril diameters.
• Chemical extraction of pectic polysaccharides from *A. thaliana* cell walls to assess their impact on microfibril width.

Main Results:

• Tightly interwoven microfibrils with uniform diameters were observed: 4.4±0.13 nm in onion and 5.8±0.17 nm in *A. thaliana*.
• Extraction of pectic polysaccharides reduced *A. thaliana* microfibril width to 3.2±0.13 nm.
• The measured microfibril widths align with models where each microfibril contains a single cellulose crystallite.

Conclusions:

• The study provides precise measurements of angiosperm primary cell wall microfibril dimensions.
• Results strongly support the hypothesis that individual microfibrils contain only one cellulose crystallite.
• This finding refines our understanding of cellulose organization and cell wall architecture.