Analysis of the Structural Role of Key Cell Wall Components in Arabidopsis thaliana via SAXS and GIWAXS

Restricted (Penn State Only)
- Author:
- Martin, Benjamin
- Area of Honors:
- Chemical Engineering
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Esther Gomez, Thesis Supervisor
Michael John Janik, Thesis Honors Advisor - Keywords:
- SAXS
GIWAXS
Arabidopsis thaliana
Cell Wall
Pectin
Cellulose
Xyloglucan
Growth Media
Methyl Esterification - Abstract:
- The plant cell wall is a promising biomaterial for many purposes, including as a renewable fuel source, but the structure, formation, and interactions between cell wall components are not yet fully understood. We aim to gain insights into the role and relative effect of several of the components of the primary cell wall using data from small angle x-ray scattering (SAXS) and grazing incidence wide angle x-ray scattering (GIWAXS) to determine the alignment, spacing, and relative degree of crystallinity for key cell wall component-deficient mutants and wild-type Arabidopsis thaliana. In this thesis, we examine the changes in alignment and spacing between cellulose microfibrils caused by decreasing the abundance of cell wall components including pectin, xyloglucan, and cellulose. This is achieved through examination of plants with genetic mutations to specific cell wall components. Mutations of interest include qua2 (pectin-reduced), xxt1/2 (xyloglucan-reduced), cesa3je5 (CESA3/cellulose-reduced), and prc1 (CESA6/cellulose-reduced), and these plant materials are compared against wild-type Arabidopsis as measured by SAXS. The second aim of this thesis focuses on examining how calcium, boric acid, and methyl esterification of pectin impact the cellulose crystal alignment, spacing, and relative degree of crystallinity of cellulose microfibrils. Mutations of interest include cgr2/3 (homogalacturonan methyl esterification-reduced) and GoSAMT (Golgi S-adenosyl methionine transporter-reduced), and cell walls from these mutants are compared to wild-type Arabidopsis as measured by SAXS and GIWAXS. Further, these samples were grown in either calcium-enriched, boric acid-enriched, calcium- and boric acid-enriched, or control media to evaluate the effects of media composition on the cross-linking of the plant cell wall. We found that qua2 and cesa3je5 mutants showed significantly decreased cellulose microfibril alignment indicating that pectin and cellulose levels are important factors for alignment. Further, we found that qua2 mutants showed significantly different cellulose microfibril spacing in one of the two datasets, indicating that pectin may be an important factor in determining spacing. The spacing and alignment for wild-type Arabidopsis was also found to be correlated with age for immature hypocotyls. Some mutation and media combinations yielded significant differences in cellulose crystal alignment, microfibril alignment, and relative degree of crystallinity, but few consistent trends were observed. These factors should be studied further with additional testing, prioritizing high-variance sample groups.