Reduced Petal Pigmentation in Lisianthus (Eustoma grandiflorum) Flowers under Low Light Conditions Is Associated with Decreased Expression of Anthocyanin Biosynthesis Genes

Cut flowers such as lupinus, delphinium, salvia and snapdragon, bearing inflorescence with florets at various developmental stages, are harvested when the first floret opens. The younger florets in the inflorescence are able to complete their development indoors in the vase, but usually with significantly reduced color. In many cases the open florets remain almost colorless when the cut flowers are placed in the vase. These observations suggest that pigment biosynthesis in petals is controlled by light intensity. The aim of this study was to explore the significance of low light intensity, typical for interior conditions, to the observed reduction in anthocyanin levels and its consequence to the expression of anthocyanin biosynthetic genes in petals of lisianthus (Eustoma grandiflorum) flowers. Lisianthus is a good model system for this type of research, as its anthocyanin biosynthetic pathway, the relevant anthocyanin biosynthetic genes and the effect of light on pigment accumulation in its petals were well documented. Our data show that low light conditions result in reduced anthocyanin content in petals of developing florets both in cut flowers and potted plants. We have measured the expression of six genes encoding for the different enzymes in the delphinidin (blue-violet color) biosynthetic pathway in developing petals. These included: chalcone synthase (CHS), chalcone isomerase (CHI), flavanone-3-hydroxylase (F3H), flavonoid-3',5'-hydroxylase (F3'5'H), dihydroflavonol-4-reductase (DFR) and anthocyanidin synthase (ANS). Also, the expression of one gene leading to flavonol biosynthesis, flavonol synthase (FLS), was assayed. Although the various genes had different expression patterns during petal development, for all of them the expression was reduced in a similar manner under low light conditions. These results suggest that light intensity regulates a master transcription factor common for all these anthocyanin biosynthesis genes.