Floral color change in Viola cornuta L. (Violaceae):: a model system to study regulation of anthocyanin production

Open flowers of Viola cornuta (Violaceae) cv. Yesterday, Today and Tomorrow (YTT) undergo a striking color change from white to purple over 5-8 days. In this paper we describe the physiological and biochemical bases of the color change, and examine possible environmental signals that influence anthocyanin expression. High performance liquid chromatography (HPLC) analysis was used to identify malvidin as the major anthocyanidin and myricetin as the major copigment in YTT. The amount of malvidin increases as color appears, while the myricetin concentration remains constant. A slight decrease in petal pH values as the flowers age is not sufficient to cause a color change. Comparison of emasculated and intact flowers shows that the presence of pollen on the stigma is necessary to produce the color change. YTT flowers exposed to light change color while those maintained in darkness do not. Applying an ethylene inhibitor, silver thiosulphate, does not prevent color change. The increase in malvidin over time suggests that anthocyanin synthesis is upregulated by proximate triggers such as pollination and light. YTT presents an excellent model system for the study of anthocyanin regulation because it is a floriferous annual, the appearance of color is easily triggered, and only one anthocyanin is involved. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.