Flavonoids delphinidin

The riocus encodes the enzyme flavonoid 3 -hydroxylase (F3 H) [17, 18], and is an important controller of flux in the anthocyanin pathway in soybean seed coats (Fig. 4.1). F3 H diverts metabolic flux away from biosynthesis of orange (pelargoni-din) and blue (delphinidin) anthocyanins toward the red cyanidin-3-(9-glucoside, which is the main anthocyanin in the seed coats of black soybean [7, 8]. T increases the accumulation of delphidin-3-O-glucoside in black seed coats, even though it is not required for its biosynthesis [19]. Possible mechanisms for this include positive feedback, or the stabilization of the putative anthocyanin biosynthetic metabolon [20] by F3 Fl-derived membrane anchoring (Fig. 4.1). 

The W1 locus encodes flavonoid 3 5 -hydroxylase F3 5 H) [21]. F3 5 H diverts metabolic flux into the blue delphinidin branch of anthocyanin biosynthesis (Fig. 4.1). In the absence of F3 H activity (f), Wi and recessive wl give imperfect black and buff seed colors, respectively [10]. However, in black seeds, F3 H (T) phenotypically masks Wl. In contrast to its role in seeds, Wl has a prominent role in flower colors, as delphinidin-based anthocyanins are the major pigments in purple soybean flowers [22, 23]. Interestingly, F3 5 H is expressed at very low levels in flowers and seeds [21]. This suggests that, out of the two branch-point genes (i.e., F3 H and F3 5 H), it is the strong expression of F3 H in seed coats and weak expression in the flowers that determines preferential accumulation of cyanidin-based and delphinidin-based anthocyanins in these respective tissues [21]. 

Katsumoto Y, Fukuchi-Mizutani M, Fukui Y et al (2007) Engineering of the rose flavonoid biosynthetic pathway successfully generated blue-hued flowers accumulating delphinidin. Plant Cell Physiol 48 1589-1600... 

Okinaka, Y. et al.. Selective accumulation of delphinidin derivatives in tobacco using a putative flavonoid 3, 5 -hydroxylase cDNA from Campanula medium. Bioscl Biotechnol Biochem., 67,161, 2003. 

Parasitic plants often use chemicals released by their host plant to stimulate seed germination, to locate the host, or for haustorial development. Many different compounds are involved, including strigolactones, quinones, coumarins, flavonoids, and other phenolics. Flavonoids contribute to signaling in some species but not others. Haustorial development in Triphysaria versicolor can be induced in vitro by the anthocyanidins petunidin, cyanidin, pelargonidin, delphinidin, as well as their glycosides obtained from the host plant.Anthocyanins are not usually found in root exudates, however, and thus the mechanism by which they affect natural signals for parasitic plants in the soil is not clear. 

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