Combined analysis of inorganic elements and flavonoid metabolites reveals the relationship between flower quality and maturity of Sophora japonica L

Abstract

Flos Sophorae (FS), or the dried flower buds of Sophora japonica L., is widely used as a food and medicinal material in China. The quality of S. japonica flowers varies with the developmental stages (S1-S5) of the plant. However, the relationship between FS quality and maturity remains unclear. Inductively coupled plasma optical emission spectrometry (ICP-OES) and ultra-high performance liquid chromatography coupled with electrospray ionization-triple quadrupole-linear ion trap mass spectrometry (UPLC-ESI-Q TRAP-MS/MS) were used to analyze inorganic elements and flavonoid metabolites, respectively. A combined analysis of the inorganic elements and flavonoid metabolites in FS was conducted to determine the patterns of FS quality formation. Sixteen inorganic elements and 173 flavonoid metabolites that accumulated at different developmental stages were identified. Notably, 54 flavonoid metabolites associated with the amelioration of major human diseases were identified, and Ca, P, K, Fe, and Cu were postulated to influence flavonoid metabolism and synthesis. This study offers a novel perspective and foundation for the further exploration of the rules governing the quality of plant materials.

Keywords: Sophora japonica; flavonoid metabolites; inorganic elements; maturation; quality change.

Figure 1

Phenotypic features and inorganic elements in Flos Sophorae (FS). (A) Inflorescence morphology of S. japonica. (B) Phenotypic features of FS in the five developmental stages (S1–S5). (C) Heavy-metal elements. (D) Trace elements. (E) Macroelements. Different letters indicate significant differences (p < 0.05).

Figure 2

Multivariate statistical analysis of the flavonoid metabolites in different flower maturity of S. japonica. (A) Classification of flavonoid metabolite structure. (B) Principal component analysis of the flavonoid metabolites. (C) Hierarchical cluster analysis of the flavonoid metabolites. (D) K-means cluster analysis of the flavonoid metabolites.

Figure 3

Differential flavonoid metabolite analysis of the samples in the five developmental stages of S. japonica. (A–D) Orthogonal partial least squares-discriminant analysis model plots for the following comparisons: S1 vs. S2, S2 vs. S3, S3 vs. S4, and S4 vs. S5, respectively. (E–H) Volcano plots show the expression levels of the differential flavonoid metabolites in the comparisons S1 vs. S2, S2 vs. S3, S3 vs. S4, and S4 vs. S5, respectively. Each dot represents a metabolite: red dots indicate upregulated flavonoid metabolites; green dots indicate downregulated flavonoid metabolites; and black dots indicate flavonoid metabolites detected with insignificant expression differences. (I) The Venn diagram indicates the common and unique metabolites in the comparison groups.

Figure 4

Partial pathway map of the differential flavonoid metabolites in Flos Sophorae. Grey represents the phenylpropanoid synthesis pathway; red represents the isoflavone synthesis pathway; yellow represents the anthocyanin synthesis pathway; blue represents the flavonoid synthesis pathway; and green represents the flavone and flavonol synthesis pathway.

Figure 5

Inorganic elements–differential metabolites–metabolic pathways correlation network. The red diamond represents an inorganic element; the orange ellipse represents an enzyme; the purple ellipse represents differential metabolite; and the green hexagon represents a metabolic pathway.