Heat Stress during Soybean Seed Development Results in Different Metabolite Profiles in Heat Sensitive and Tolerant Genotypes.

Soybean is one of the predominant crop plants grown worldwide. In the MidSouth region of the United States, endemic late season drought stress has resulted in an alteration of agronomic practices that improves yield and farm return on investment(Early Soybean Production System)., but has increased heat stress during seed development High yielding soybean cultivars have extremely limited genetic diversity, and heat stress typically results in decreased seed quality and vigor, as well as increased Phomopsis longicolla infection. A plant introduction line, (PI 587982A) displays remarkable resistance to these negative impacts of heat on seed development, and has been used to develop experimental breeding lines. In this study, we compared global metabolome of mature seeds from tolerant and conventional lines exposed to one of three different temperature regimes: optimal (28°C), moderate stress (35°C), or high stress (42°C) during their seed development/maturation. Seeds of both genotypes displayed equivalent germination when produced at 28 º C. In contrast, seeds produced at 35 ºC resulted in 50% loss of germination for conventional seeds, whereas germination of a tolerant linewas unaltered. At 42 ºC, seeds of a conventional line completely failed to germinate, while the tolerant seeds displayed ~20% germination rates. Genotypic comparisons were carried out on 275 seed compounds, of which 38 and 54 metabolites were significantly different (P < 0.05) between genotypes at 28°C and 35°C, respectively. Antioxidants and secondary metabolites were ranked highest among the most significantly different metabolites. These included Gulono 1,4-lactone, several tocopherol species, and numerous phenylpropanoid-pathway derivatives, which were significantly higher in tolerant seeds relative to conventional seed. The higher abundance of antioxidants and anti-oxidant secondary metabolites are likely responsible for quenching free radicles produced at 35°C and in maintaining higher germination rates.