Impact of heat stress during seed development on soybean seed metabolome

Seed development is a temperature-sensitive process that is much more vulnerable than vegetative tissues to abiotic stresses. High temperatures during soybean (Glycine max) seed development frequently results in seed with poor germination, increased incidence of pathogen infection, and decreased economic value. Climate change is expected to increase the incidence and severity of summer heatwaves, and the impact of heat stress on seed development will become more widespread during the course of the twenty-first century. Global metabolite profiles were contrasted between seed from heat-tolerant and heat-susceptible genotypes produced under 28/22 degrees C (control), 36/24 degrees C, and 42/26 degrees C day/night temperatures. Germination of seeds from the heat-susceptible genotype was strongly reduced (50 %) for the 36/24 degrees C treatment and completely inhibited for the 42/26 degrees C. In contrast, germination was unaffected for the heat-tolerant genotype for the 36/24 degrees C, and while strongly inhibited, some (25 %) seed from the heat-tolerant genotype were able to germinate even for the 42/26 degrees C treatment, and in general were less impacted by elevated temperatures as compared to a commonly grown high-yielding, but heat-sensitive genotype. A total of 275 seed metabolites were analyzed by three metabolite profiling methods, and genotype-specific differences and temperature specific differences were identified. A diverse set of antioxidant metabolites, including tocopherols, flavonoids, phenylpropanoids, and ascorbate precursors were found to be enriched in seed of the heat tolerant genotype. The generally greater abundance of these metabolites at both temperatures in the tolerant genotype indicates that these compounds are likely responsible, at least in part, for the greater tolerance to high temperatures during seed development.