Comparative Metabolic Profiling Reveals Secondary Metabolites Correlated with Soybean Salt Tolerance

High-performance liquid chromatography−ultraviolet−electrospray ionization mass spectrometry (HPLC-UV-ESI-MS) and HPLC-ESI-MSn analysis methods were used for metabolic profiling and simultaneous identification of isoflavonoids and saponins in soybean seeds. Comparative targeted metabolic profiling revealed marked differences in the metabolite composition between salt-sensitive and salt-tolerant soybean varieties. Principle component analysis clearly demonstrated that it is possible to use secondary metabolites, for example, isoflavones and saponins, to discriminate between closely related soybean genotypes. Genistin and group B saponins were identified as the key secondary metabolites correlated with salt tolerance. These individual metabolites may provide additional insight into the salt tolerance and adaptation of plants.