Differences in the Metabolic Response to Osmotic Stress Between Triticum aestivum L. and Two Ecologically Disparate Aegilops biuncialis Vis. Genotypes Differing in Drought Tolerance

Drought-induced osmotic stress reduces the growth and yield of bread wheat (Triticum aestivum L.) worldwide. Several genotypes of its wild relative, goatgrass (Aegilops biuncialis Vis.) are often tolerant to environmental stresses and used as a gene source for wheat improvement. The Aegilops accessions Ae.b. 382 and Ae.b. 642 collected from contrasted agroecological habitats may represent different defence mechanisms to osmotic stress compared to three bread wheat genotypes with various drought tolerances. The effect of a 1-week 15% polyethylene glycol (PEG) treatment on various physiological and biochemical parameters was compared at the 2-leaf stage. The osmotic stress-induced reduction in shoot length and fresh weight in all genotypes except for Ae.b. 382. This tolerance of Ae.b. 382 can derive from the greater PEG-induced accumulation of the antioxidant hydroxymethyl-glutathione in the shoots compared to other genotypes. It is due to an elevated synthesis of its precursors, cysteine and gamma-glutamylcysteine. In addition, the level of oxidative stress was smaller in Aegilops biuncialis genotypes, shown by the decrease in H₂O₂ and GSSG levels in roots and shoots, respectively. The amount of gamma-glutamylcysteine was greater in their roots than in the wheat genotypes. Furthermore, PEG treatment resulted in a greater level of putrescine, as well as the expression of defence-related genes encoding Glutathione Reductase (GR), cold-regulated protein Wcor and DihydroFlavonol-4-Reductase (DFR) in the shoots of both Aegilops accessions compared to the three wheat genotypes. Based on these differences, certain Aegilops genotypes may serve as a genetic source for the improvement of the stress tolerance of bread wheat.