Analyses of the Cell Wall Modification of Wheat Cultivars Infested with Diuraphis noxia

Wheat infested with Diuraphis noxia (Russian wheat aphid: RWA) respond by inducing a range of defense processes at the morphological, physiological, molecular, and biochemical levels. The physiological response includes the cell wall modification, which is generally weakened by the RWA infestation in the susceptible cultivar, while in the resistant cultivar, the cell wall modification leads to a more robust and strengthened wall. Direct measurements of the cell wall have been a challenge, but in the last decade, extraction methods for cell wall components, i.e., cellulose, hemicellulose and lignin, have been measured accurately. In addition, the Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses provide additional physicochemical analysis. The acid and alkaline solutions extractions of the cell wall major components quantify the cellulose, hemicellulose, and lignin changes (in percentages) that occur during RWA-wheat interaction. The FTIR is promising to study the cell wall chemical changes (phenolics, ester bonds, glycosidic linkages, and a broad band between 3400 and 3000 cm^-1 assigned to hydroxylic groups, inter and intra-hydrogen bonds that form due to cellulose) that occur due to RWA infestation. Last, the XRD is useful to show the plant cell wall's biophysical changes (microcrystalline cellulose degree of crystallinity changes) due to RWA infestation. In this chapter, we present methods for analyzing cell wall modification of susceptible and resistant wheat cultivars infested with RWA, using extractions, FTIR, and XRD techniques.