None named naringenin. The oxidation on the latter compound by flavanone 3-hydroxylase (F3H) yields the dihydrokaempferol (colourless dihydroflavonol) that subsequently is usually hydroxylated on the 3′ or 5′ position in the B-ring, by flavonoid 3′-hydroxylase (F3’H) or flavonoid 3′,5′-hydroxylase (F3’5’H), generating, respectively, dihydroquercetin or dihydromyricetin. Naringenin may possibly also be straight hydroxylated by F3’H or F3’5’H to deliver, respectively, eriodictyol and pentahydroxy-flavanone, that are once more hydroxylated to dihydroquercetin and dihydromyricetin. The three dihydroflavonols thus synthesized are then converted to anthocyanidins (coloured but unstable pigments) by two reactions catalysed by dihydroflavonol reductase (DFR) and LDOX. The DFR converts dihydroquercetin, dihydrokaempferol and 5-LOX Purity & Documentation dihydromyricetin to leucocyanidin, leucopelargonidin and leucodelphinidin (colourless flavan-3,4-cis-diols), respectively. Subsequently, LDOX catalyses the oxidation of leucocyanidin, leucopelargonidin and leucodelphinidin to cyanidin (red-magenta anthocyanidin), pelargonidin (orange anthocyanidin) and delphinidin (purple-mauve anthocyanidin), respectively. All of the colours above talked about refer to a SIRT7 Biological Activity precise environmental situation, i.e., when the anthocyanidins are in an acidic compartment. The last prevalent step for the production of coloured and steady compounds (anthocyanins) requires the glycosylation of cyanidin, pelargonidin and delphinidin by the enzyme UDP-glucose:flavonoid 3-O-glucosyl transferase (UFGT). Lastly, only cyanidin-3-glucoside and delphinidin-3-glucoside could be further methylated by methyltransferases (MTs), to become converted to peonidin-3-glucoside and petunidin- or malvidin-3-glucoside, respectively. The synthesis of PAs branches off the anthocyanin pathway after the reduction of leucocyanidin (or cyanidin) to catechin (or epicatechin) by the enzymatic activity of a leucoanthocyanidin reductase (LAR), or anthocyanidin reductase (ANR) [30]. The subsequent actions take spot in the vacuolar compartments, exactly where the formation of PA polymers occurs by the addition of leucocyanidin molecules towards the terminal unit of catechin or epicatechin, possibly catalysed by laccase-like polyphenol oxidases. Having said that, the localization of those enzymes and their actual substrates are nonetheless controversial [31,32].Int. J. Mol. Sci. 2013,Figure 1. (A) Scheme in the flavonoid biosynthetic pathway in plant cells. Anthocyanins are synthesized by a multienzyme complicated loosely connected to the endoplasmic reticulum (CHS, chalcone synthase; CHI, chalcone isomerase; F3H, flavanone 3-hydroxylase; F3’H, flavonoid 3′-hydroxylase; F3’5’H, flavonoid 3′,5′-hydroxylase; DFR, dihydroflavonol reductase; LDOX, leucoanthocyanidin oxidase; UFGT, UDP-glucose flavonoid 3-O-glucosyl transferase; MT, methyltransferase). Proanthocyanidins (PAs) synthesis branches off the anthocyanin pathway (LAR, leucoanthocyanidin reductase; ANR, anthocyanidin reductase; STS, stilbene synthase); the black arrows refer to biosynthetic methods missing in grapevine. Numbers next to the flavonoid groups are related towards the chemical structures shown in (B). (B) Chemical structures with the big flavonoid groups.(A)(B)Int. J. Mol. Sci. 2013, 14 3. Mechanisms of Flavonoid Transport in Plant CellsIn the following section, recent advances on the models of flavonoid transport into vacuole/cell wall of unique plant species, ascribed to a common membrane transporter-mediated transport (MTT), will b.