yellow A. longissima or A. chrysantha produce anthocyanins, confirming independent mutations blocking anthocyanin production (Prazmo, 1965; Taylor, 1984). Finally, Prazmo’s factor F is a mutation that most likely affects either the expression or the function of F3′5′H (Fig. 2.3), because blue/purple-flowered species of Aquilegia primarily produce delphinidins [Fig. 2.2; Taylor (1984)].
Biochemical analyses of anthocyanins found in Aquilegia species have also been conducted (Taylor and Campbell, 1969; Taylor, 1984; Whittall et al., 2006b). These studies suggest that losses of floral anthocyanins are likely caused by changes in expression patterns of the core enzymatic genes of the ABP or changes causing substrate flux away from anthocyanin production. In an extensive analysis of flavonoids and other phenolic compounds, Taylor and Campbell (1969) found that species that lack floral anthocyanins (A. pubescens, A. longissima, A. flavescens) all produce anthocyanins in other tissues. Thus, genes in the ABP must be functional and, if expressed, would result in flowers with anthocyanins. Similarly, Whittall et al. (2006b) found that both flavones and flavonols are produced in the flowers of species that lack anthocyanins, confirming that the genes expressed early in the ABP are functional.
In an analysis of floral anthocyanins, Taylor (1984) found that species with blue/purple flowers produced either just delphinidins or a combination of delphinidins and cyanidins, whereas red-flowered species produced both cyanidins and pelargonidins. From North America, he included 2 red-flowered species (Aquilegia formosa and Aquilegia canadensis) and 2 blue-flowered species (Aquilegia brevistyla and Aquilegia coerulea). According to our reconstruction of ancestral flower colors (Fig. 2.2), these species represent the descendants of 1 shift from blue to red (A. canadensis from the common ancestor with A. brevistyla) and 1 shift from red to blue (the A. coerulea clade from the common ancestor with the A. formosa clade). The first case likely resulted from loss of function or down-regulation of F3′5′H and a concomitant increase in flux down the cyanidin and pelargonidin portions of the ABP. This finding suggests that DFR in the ancestor of A. canadensis was a substrate generalist, unlike some taxa (e.g., Nicotiana) where DFR is specialized for the products of F3′H and F3′5′H and cannot act on the product of F3′H to produce red pelargonidins (Nakatsuka et al., 2007). The second case appears to be an example of a reversal, with the recovery of F3′5′H activity and delphinidin production. Interestingly, F3′5′H is likely expressed and functional in rare individuals of A. pubescens with blue-lavender flowers (Chase and Raven, 1975), suggesting that a functional copy of this gene has been maintained in this species as well.