Metabolomics Analysis Reveals the Role of Cyanidin Metabolism in Plumbago auriculata Flower Color

Abstract

Blue flowers, which are rare, have long been a focus for researchers engaged in colored flower breeding. In this study, Plumbago auriculata, a plant with blue flowers, and its white flower forma Plumbago auriculata f. alba were used as research materials. Flower color quantification, environmental scanning electron microscopy (ESEM) observation of petal epidermal cells, and determination of the cell sap pH were carried out; moreover, metabolomic analysis was used to analyze the flavonoid metabolites of both types of petals. The results showed that the flower color of P. auriculata was bluish violet, and there was no significant difference in the epidermal cell distribution of the white and blue petals. The key substance that determined the bluish violet flower color was cyanidin-3-O-(6″-p-coumaroylglucoside) (Cy3-pC·G). Compared to the white petal cells, the blue petal cells exhibited up to 40 upregulated flavonoid compounds that were copigments. Together with the significantly increased pH (5.92 ± 0.12) of the petal cell sap, these copigments affected the color presentation of Cy3-pC·G, causing the final petal color of P. auriculata to be bluish violet. The results of this study indicate that cyanidin is an important anthocyanidin in blue flowers, which provides new insights into the breeding of blue flowers.