Assessment of Metabolic Profiles in Florets of Carthamus Species Using Ultra-Performance Liquid Chromatography-Mass Spectrometry

Abstract

The genus Carthamus is a diverse group of plants belonging to the family Compositae. Florets of Carthamus species exhibit various colors, including white, yellow, orange, and red, which are related to their metabolite compositions. We aimed to investigate the metabolites accumulated in florets of three wild (C. lanatus, C. palaestinus, and C. turkestanicus) and one cultivated (C. tinctorius) species of safflower at three developmental stages. Metabolites were extracted from freeze-dried florets using 70% methanol; qualification and quantification were carried out using liquid chromatography quadrupole time-of-flight mass spectrometry in positive and negative ion modes followed by extraction of the peaks. Fifty-six metabolites, including phenylpropanoids, chalcones, isoflavonoids, flavanones, flavonols, flavones, and other primary metabolites, were identified for the first time in safflower wild species. The orange florets contained high abundances of safflomin A, anhydrosafflor yellow B, and baimaside, whereas white/cream and light-yellow pigmented florets had high abundances of 1,5-dicaffeoylquinic acid, luteolin 7-O-glucuronide, and apigenin 7-O-β-D-glucuronide. The principal component analysis clearly distinguished the samples based on their pigment types, indicating that color is a dominant factor dictating the identity and amount of the metabolites. Pearson correlation data based on levels of metabolites showed that orange and yellow florets were significantly correlated to each other. White and cream pigmented species were also highly correlated. Comparison between three developmental stages of safflower wild species based on their metabolite profile showed inconsistent. The findings of this study broaden the current knowledge of safflower metabolism. The wide diversity of metabolites in safflower materials also helps in efforts to improve crop quality and agronomic traits.

Keywords: LC-ESI-QTOF-MS; florets; metabolites; pigment; safflower wild species.

Figure 1

Phenotypes of wild safflowers and cultivars. Safflower materials were obtained from the USDA (U.S. Department of Agriculture) National Plant Germplasm System via the Germplasm Resource Information Network. C. tinctorius and C. palaestinus florets were orange at the middle stage and became red/orange as development proceeded. Florets of W6 16791 and PI 426425 were yellow at the middle stage, and the pistils became orange as development proceeded. All other materials were white/cream at the middle stage.

Figure 2

Heat maps comparing the levels of phenylpropanoids, chalcones, and flavonoids in safflower wild species. Relative peak areas were normalized to construct a comparative heat map. The abscissa at top displays the names of the samples, and the ordinate at right displays the names of the metabolites. The deeper the red color, the higher the peak area of the metabolites; the deeper the blue color, the lower the peak area of the metabolites. Sample name abbreviations: the first two letters indicate the first two letters of the species name, the number indicates the last digit of the PI number, and the letters E, M, and L indicate early, middle, and late stages of development, respectively. For example, “ti1E” indicates the sample PI 592391 (C. tinctorius) at the early stage of development.

Figure 3

Loading (A) and score (B) plots of principal components 1 and 2 from the principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) (C) and variable importance in projection (VIP) scores associated with metabolites (D) of wild and cultivated safflower species. Sample name abbreviations: the first two letters indicate the first two letters of the species name, the number indicates the last digit of the PI number, and the letters E, M, and L indicate early, middle, and late stages of cultivation, respectively. For example, “ti1E” indicates the sample PI 592391 (C. tinctorius) at the early stage of development.

Figure 4

Cumulative distribution of chalcones (A), isoflavonoids (B), flavones (C), and flavonols (D) in wild safflower florets at different developmental stages. Sample name abbreviations: the first two letters indicate the first two letters of the species name, the number indicates the last digit of the PI number, and the letters E, M, and L indicate early, middle, and late stages of development, respectively. For example, “ti1E” indicates the sample PI 592391 (C. tinctorius) at the early stage of development.

Figure 5

Simplified integrated metabolic pathways of phenylpropanoid, chalcone, isoflavonoid, flavanone, flavone, and flavonol biosynthesis in the florets of wild and cultivated safflower species.