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Anthocyanins are the major flower pigments in higher plants. In most cases, anthocyanin accumulation is an integral part of flower development and the processes of petal pigmentation and cell expansion are tightly linked. Activation of the anthocyanin pathway during petal development requires a complex interaction between environmental and developmental signals. Using Petunia hybrida flowers as a model, some of these signals were identified and characterized. Gibberellins (GAs), sugars and light were shown to be required for the induction of anthocyanin gene transcription and for accumulation of the pigment in the developing corolla. It was also shown that the effect of these signals is not specific for the pigment's biosynthesis, they also control petal cell expansion and induce the expression of genes from various pathways. These results support a model in which GAs, light and sugars promote the activity of master transcription regulators that control various pathways to complete the entire process of flower development.