Abstract
Exposure of the plant cell wall to biotic and abiotic stresses results in structural and chemical changes. Russian wheat aphid (RWA) infestation severely damages wheat plants, releasing cell wall-degrading enzymes that compromise cell wall integrity. This study aims to elucidate the cell wall modifications in resistant wheat cultivars during RWA infestation. Three wheat cultivars with distinct resistance phenotypes to the RWA South African biotype 2 (RWASA2) were grown in the glasshouse. At the three-leaf stage, the seedlings were infested with RWASA 2 for 14 days. The leaf samples harvested at 2, 7, and 14 days post-infestation (dpi) were used to study cell wall modifications in the RWASA 2-infested cultivars, focusing on cellulose, hemicellulose, callose, and lignin contents. The results showed that post-RWASA2 infestation, the resistant Tugela-Dn5 significantly increased the hemicellulose content by 2.8- and 1.3-folds at 2 and 14 dpi, respectively, while the Tugela and Tugela-Dn1 significantly decreased the hemicellulose content at 2, 7, and 14 dpi. Tugela-Dn5 also increased the cellulose content by 1.4-fold and 2.2-fold at 7 and 14 dpi, respectively. The acid-soluble lignin content significantly increased in the infested Tugela-Dn5 compared to uninfested at 2 and 14 dpi, while it significantly decreased in Tugela and Tugela-Dn1. Callose levels also increased in all cultivars at 2 dpi, but only the infested Tugela-Dn5 exhibited an increase in callose content compared to the uninfested at 14 dpi. The extracted contents of the increased cellulose, hemicellulose, and lignin in Tugela-Dn5 were corroborated by FTIR analysis, which showed broad peaks at 3300 cm(-1) representing the OH functional group and inter- and intra-hydrogen bonds within the increased cellulose in Tugela-Dn5. No significant reduction of lignin peaks at 1600 to 1578. 99 cm(-1) assigned to the phenolic groups was observed in Tugela-Dn5. These findings place cell wall modifications at the centre of the wheat's physiological resistance response to aphid infestation, particularly the reinforcement of the cell wall that persists for 14 dpi.