Inhomogeneity of Cellulose Microfibril Assembly in Plant Cell Walls Revealed with Sum Frequency Generation Microscopy

Area of Science:

• Biophysics
• Plant Biology
• Spectroscopy

Background:

• Sum frequency generation (SFG) vibrational spectroscopy analyzes noncentrosymmetric structures in amorphous matrices.
• Previous SFG studies focused on nanoscale and mesoscale cellulose assembly in plant cell walls.
• Averaged spectral data limits regiospecific and tissue-specific analysis in plants.

Purpose of the Study:

• To develop and demonstrate spatially resolved SFG analysis and imaging for plant cell walls.
• To overcome limitations of conventional SFG by achieving higher spatial resolution.
• To visualize the distribution of cellulose microfibrils within individual plant cells and tissues.

Main Methods:

• Combined broad-band SFG spectroscopy with optical microscopy.
• Designed a system to irradiate samples with 800 nm and tunable IR beams via a single reflective objective.
• Utilized a configuration with beams incident from opposite sides of the sample's surface normal.

Main Results:

• Achieved spatially resolved SFG analysis and imaging of plant cell walls.
• Revealed inhomogeneous distributions of cellulose microfibrils within single cell walls (e.g., cotton fibers, onion epidermis).
• Demonstrated tissue-specific variations in cellulose microfibril distribution in Arabidopsis and bamboo.

Conclusions:

• SFG microscopy provides regiospecific and tissue-specific vibrational spectroscopic imaging of plant cell walls.
• This technique offers a powerful complement to existing methods like FTIR and Raman microscopy.
• SFG microscopy has broad applicability for vibrational imaging in diverse biological systems.