Plant cell wall is a complex, multi-polymeric system that consists of primarily carbohydrates and lignin. Cellulose strands come together to form microfibrils while the amorphous polymers, hemicellulose and lignin form a network structure and fill the interstitial space. Small-angle neutron scattering is ideally suited to visualize complex hierarchical structures like biomass. However, neutron sensitivity of the different plant biopolymers are similar making structural association non-trivial and ambiguous. A promising approach is partial deuteration which is designed to increase the difference in the neutron sensitivity between amorphous carbohydrate and lignin. Here, we will present the results from multiple partially deuterated plants- Switchgrass, Brassica Oleracea (Kale), and Eucalyptus. Partially deuterated switchgrass plants were cultivated in hydroponic media containing 50% D2O to produce tiller biomass with 34% deuterium incorporation determined by NMR and contrast variation small-angle neutron scattering (CV-SANS). The chemical and physical properties were found to be similar to the same cultivar grown hydroponically in H2O, but with slightly increased lignin content and changed lignin deposition patterns (by TEM) and less recalcitrance to enzymatic hydrolysis. Partially deuterated Kale was cultivated in 31% deuterated media under hydroponic conditions. Fourier-transform infrared spectroscopy (FTIR) results indicated that D/H substitution for carbohydrate is higher than for lignin and by combining CV-SANS and FTIR, it was determined that 50% of covalently bonded hydrogens were replaced with deuterium atoms in cellulose while only 10% for lignin. Similar results were observed for partially deuterated Eucalyptus plants too. These results open new avenues to deconvolute structural features of amorphous plant polymers in the plant cell wall simultaneously from those of the well-organized cellulose microfibrils.

Deuterium labelled plants enable deconvolution of plant cell wall biopolymer component structures using neutron scattering

ACS Spring Meeting 2021

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