Nanoscale Structural Study of Genetically Modified Arabidopsis Thaliana by X-Ray Radiation

Cellulose is the most abundant natural material on Earth. New ways to utilize the limited resources on Earth for the benefit of the human kind can be found by studying genetically modified plants. The nanoscale structure of organic matter is important to its macroscopic properties. Natural materials can be characterized by measuring the degree of crystallinity in the material and the average dimensions of the crystallites. The cellulose crystallites are helically wound as long fibrous microfibrils in which crystalline and less ordered (amorphous) regions alternate. The microfibril angle (MFA) is the angle of these microfibrils with respect to the cell axis and it is linked with the longitudinal stiffness of the material. A wide-angle X-ray scattering (WAXS) method can be used to study these nanoscale properties of the matter in a non-destructive manner. Arabidopsis thaliana (AT) is an important model system for plant biology. It is a widely spread small flowering plant with a short life cycle and a relatively small genome which has been fully sequenced. X-ray microtomography confirmed that the AT cells are generally round rather than rectangular unlike xylem cells. The cellular structure of the plants was not destroyed in the WAXS measurements. The resolution obtained from the measurements of samples with natural humidity was not sufficient hence all the samples were measured dry. A total of 62 samples were measured with the WAXS set-up, 15 of them wild type plants and the rest genetically modified. In this study the WAXS data analysis methods were enchanced for the benefit of the weakly scattering Arabidopsis samples. The mean crystallite width of all samples ranged from 26 to 30 Å. This is consistent with the crystallite width being determined during the biosynthesis of cellulose. The values for the degree of crystallinity ranged from approximately (20 30)% and all the average values were slightly above 25%. The mean microfibril angle varied greatly between the samples, all the way from 2 to 21 degrees. The mean values of different lines varied more for the MFA than for other properties. Statically significant differences between means of different lines were seen for one line in the degree of crystallinity, for one line in the MFA and for two lines in the crystallite width. Due to small sample sizes these differences should be considered mostly as indicative and not as conclusive evidence on the effects of the genetic modification.