In plant cell walls, movement of cellulose synthase complex (CSC) regulates the cellulose microfibril deposition. By tagging CSCs with fluorescent tags and monitoring their movements with fluorescent microscopic imaging, previous studies have shown that the CSC movement is bidirectional in primary walls, while it can be biased toward unidirectional in induced secondary walls. This study explores the use of non-linear optical spectroscopy technique called sum frequency generation (SFG) to determine the net polarity of cellulose microfibrils in plant cell walls. Previously, DFT calculations suggested that SFG can distinguish parallel vs antiparallel packing of adjacent cellulose crystallites. The current study considers the effect of phase-mismatch between incoming and outgoing beams as well as the inter-crystallite separation. Theoretical calculations based on the nonlinear optics theory predicted how the SFG intensity will vary with the inter-crystallite distance for a given experimental geometry with a fixed coherence length of the SFG process. The theoretically-predicted trend was confirmed by measuring cellulose suspension solutions with varying concentrations. Then, the finding was applied to determine net polar order of uniaxially-aligned cellulose microfibrils along the fibril axis in a secondary xylem wall induced in the epidermis of Arabidopsis hypocotyl and cellulose fibers isolated from in vascular bundles of celery stem. To the best of our knowledge, these are the first spectroscopic evidence for biased directionality of cellulose microfibrils in certain types of plant cell walls.  <br/>

Meso-scale polarity of cellulose microfibrils in plant cell walls: Distinguishing bidirectional vs. unidirectional arrangement of fibers using sum frequency generation spectroscopy

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.