Global Metabolic Expression in Wheat Under Post-Anthesis Water Stress Conditions

Post anthesis drought is a common limiting factor for many temperate wheat growing regions including the USA. Drought causes significant changes in crop growth and yield. Metabolites are the end products of cellular regulatory processes, and their levels can be regarded as the ultimate response of biological systems to genetic or environmental changes. The advancement of metabolomics research has provided a great opportunity for the plant genetics and breeding community to develop metabolic biomarkers for genetic improvement for stress. To identify the metabolites expressed under drought conditions, we exposed soft wheat variety “SS8641” (widely grown wheat variety in Southeastern US) to drought conditions. The experiment was conducted under greenhouse conditions in University of Florida, Gainesville, and plants were subjected to two water treatments, 100% and 25% field capacity. Leaves were harvested 2 weeks post-anthesis every 3hrs during a 24h period. Each sample was mixed with an equal quantity of ground wheat leaf grown under CO₂ maintained at 97.5% ¹³C and 2.5% ¹²C (as an IROA Internal Standard).  Combined samples were extracted and analyzed by LC-MS. Ratios of paired peak areas were measured, normalized and outliers determined. In this experiment, a total of 724 IROA peaks were identified over the 48 samples analyzed in both positive and negative mode. Several hundred compounds were expressed over the 24h collection periods, including most primary metabolites, flavonoids, aglycones, anthraquinones, and a number of their respective glycosides. The most pronounced statistically significant changes were seen in amino acid, sugars and antioxidant compounds. Seventy eight compounds were significantly expressed under full irrigated and drought conditions. Some compounds like L-tyrosine, L-isoleucine, L-serine, L-aspertate, L-glutamate, 3-hydroxy-3-methylglutarate, L-threonine, D-arabinose, sedoheptulose, etc were strongly expressed. These compounds could potentially be associated with drought tolerance in wheat.