Investigation of lignin interactions and deposition in plant cell walls
Open Access
- Author:
- Pandey, Jyotsna Lavanya
- Graduate Program:
- Agricultural and Biological Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 18, 2014
- Committee Members:
- Thomas Lehman Richard, Dissertation Advisor/Co-Advisor
Thomas Lehman Richard, Committee Chair/Co-Chair
Nicole Robitaille Brown, Committee Member
Charles T Anderson, Committee Member
James David Kubicki, Committee Member
Ming Tien, Committee Member - Keywords:
- lignin
density function theory
amino acid
non-covalent interaction
monolignol
click chemistry - Abstract:
- Lignin is a natural cell wall polymer found in land plants and is a major component of lignocellulosic biomass. The presence of lignin in the plant cell walls provides recalcitrance to plant biomass, making it difficult to convert lignocellulosic biomass to sugars and other reactive intermediates during the production of biochemical and biofuels. Even though lignin is the second most abundant biopolymer on earth after cellulose, the structure and formation of lignin is very poorly understood; a better understanding of how lignin if formed is required in order to develop methods to effectively degrade it. It is quite well understood how lignin monomers or monolignols are synthesized in the cytoplasm of plant cells. However, not much is understood about how these monolignols are transported from the cytoplasm and deposited into the cell wall, cell corners and middle lamella and polymerized into lignin. This dissertation aims at understanding some of these aspects of lignification by developing methods to visualize lignin monomer deposition in plant cell walls. Lignin localization and visualization have also been attempted using fluorescent dyes and other markers, but their specificity has been a topic of contention. In this dissertation, a different approach to visualize the process of lignification was developed. Monolignol analogs that accurately imitate natural monolignols but contain a bioorthogonal alkynyl functional group were developed. These monolignols could be labeled with various tags containing an azide group using a simple click chemistry reaction. The tags explored in this dissertation include fluorescent-azide dyes, which can be visualized using fluorescence microscopy. Other tags that could be used include gold nanoparticles functionalized with an azide group, which can be visualized using electron microscopy. Monolignol analogs were fed to plant tissue and were successfully incorporated into cell walls, which is attributed to the flexibility with which multiple lignin monomers are known to be deposited into the walls. These versatile monolignol analogs provide several approaches to visualize lignin deposition, as the characteristic Raman signal for the alkyne group enables its visualization using Raman microscopy without requiring an additional labeling step that kills the plant cells. In addition to exploring the deposition of the monolignols in plant cell walls, the nature of their interactions with another wall component were explored using computational chemistry. Methods based on Density Functional Theory (DFT) were developed to study the nature and strength of non-covalent interactions between lignin dimers and individual amino acids. This computational analysis is not only helpful in understanding the nature of lignin-protein interactions that occur in cell walls but could also be helpful in developing force fields to model larger lignin-protein interactions at the molecular level in the future, and aid in designing protein modifications to lignin in the cell wall to improve degradability, strength, or other functional or structural characteristics.