The low levels of bioactive metabolites in target plants present a bottleneck for the functional food industry. The major disadvantage of soy leaves is their low phytoestrogen content despite the fact that these leaves are an enriched source of flavonols. Our study demonstrated that simple foliar spraying with 1-aminocyclopropane-1-carboxylic acid (ACC) significantly enhanced the phytoestrogen contents of the whole soy plant, including its leaves (27-fold), stalks (3-fold), and roots (4-fold). In particular, ACC continued to accelerate the biosynthesis pathway of isoflavones in the leaves for up to 3 days after treatment, from 580 to 15,439 μg/g. The detailed changes in the levels of this metabolite in soy leaves are disclosed by quantitative and metabolomic analyses based on HPLC and UPLC-ESI-TOF/MS. The PLS-DA score plot, S-plot, and heatmap provide comprehensive evidence to clearly distinguish the effect of ACC treatment. ACC was also proved to activate a series of structural genes (CHS, CHR, CHI, IFS, HID, IF7GT, and IF7MaT) along the isoflavone biosynthesis pathway time-dependently. In particular, ACC oxidase genes were turned on 12 h after ACC treatment, which was rationalized to start activating the synthetic pathway of isoflavones.
Keywords: ACC; isoflavone biosynthetic genes; metabolomic analysis; phytoestrogens; soy plants.