Isotope Delivery in Lignin: Not an Easy Path

Scientists attempt to overcome challenge of limited deuterium uptake by lignin for studies of biomass breakdown pathways.

The Science

Isotopic labeling of biological molecules has long been used to investigate complex chemical and structural interactions. In a previous study, deuterium (D) was successfully incorporated into a 50% solution of deuterated water (D2O) in three grass species and Lemna duckweed. However, while isotopic labeling with deuterium using 50% D2O in higher plants is promising for understanding plant cell wall structure, it has exhibited low deuterium uptake in lignin while higher D2O concentrations inhibit growth. In this study, the objective was to determine if deuterium isotopic labeling can be targeted to lignin through the absorption of deuterated phenylalanine by roots of growing whole plants.

The Impact

Lignin plays key roles in biomass recalcitrance, pyrolysis, biochar, manufacture of carbon fiber and other products, therefore imaging of lignin in biomass is an important research tool. By enabling deuteration of natural lignocellulosic plant biomass, unique insights can be found using nuclear magnetic resonance (NMR) and small-angle neutron scattering (SANS) and a host of other bioimaging techniques.

Summary

Researchers at Oak Ridge National Laboratory (ORNL) examined the effects of phenylalanine and deuterated phenylalanine in four species of monocotyledonous plants: two annual grasses, one perennial grass, and duckweed. Switchgrass, a dedicated bioenergy perennial crop, was observed to grow at a similar rate to the control plants when in a 2mM deuterated phenylalanine concentration well. Similarly, winter rye grain, a forage and winter cover crop, was able to tolerate deuterated phenylalanine at the same concentration. Annual ryegrass, a forage and amenity grass also used for phytoremediation and toxicity studies, had significantly reduced growth rates with phenylalanine—less inhibition was observed with deuterated phenylalanine. Duckweed, a small aquatic plant commonly used for toxicity tests, exhibited toxic effects with both phenylalanine and deuterated phenylalanine. Overall, deuterium was not incorporated at a high enough level (30-40%) for lignocellulosic neutron scattering studies. However, the observed 0.5-3% levels of deuterium incorporation may be high enough for discovery of metabolic pathways through mass spectroscopy or other imaging techniques. This research aligns with DOE’s bioenergy and environmental missions.

Principal Investigator

Barbara Evans
Oak Ridge National Laboratory
[email protected]

Related Links

BER Program Manager

Amy Swain

U.S. Department of Energy, Biological and Environmental Research (SC-33)
Biological Systems Science Division
[email protected]

Funding

This research was supported by the U. S. Department of Energy, Office of Science, through the Genomic Science Program, Office of Biological and Environmental Research, under Contract FWP ERKP752. The research at Oak Ridge National Laboratory’s Center for Structural Molecular Biology (CSMB) was supported by the U. S. Department of Energy, Office of Science, through the Office of Biological and Environmental Research under Contract FWP ERKP291, using facilities supported by the Office of Basic Energy Sciences, U. S. Department of Energy. R. Shah was partly supported by the graduate fellowship program of the Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville. C. Howard, F. Lavenhouse, and D. Ramirez, with K. Ramey as teacher-mentor, were supported by the Siemens Foundation through the Siemens Teachers As Research Scientists (STARS) summer 2014 program administered by Oak Ridge Institute of Science and Education, Oak Ridge Associated Universities. V. Cangemi, B. Kinney, C. Partee, and T. Ware were participants in the Appalachian Regional Commission/Oak Ridge National Laboratory Summer Math Science Technology Institute 2015 summer program. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U. S. Department of Energy under Contract DE-AC05-00OR22725.

References

Evans, B. R., G. Bali, A. Ragauskas, R. Shah, H. O’Neill, C. Howard, F. Lavenhouse, D. Ramirez, K. Weston, K. Ramey, V. Cangemi, B. Kinney, C. Partee, T. Ware, and B. Davidson. 2017. “Allelopathic Effects of Exogenous Phenylalanine: A Comparison of Four Monocot Species,” Planta. DOI:10.1007/s00425-017-2720-x.