None named naringenin. The oxidation with the latter compound by flavanone 3-hydroxylase (F3H) yields the dihydrokaempferol (colourless dihydroflavonol) that subsequently is usually hydroxylated around the 3′ or 5′ position with the B-ring, by flavonoid 3′-hydroxylase (F3’H) or flavonoid 3′,5′-hydroxylase (F3’5’H), producing, respectively, dihydroquercetin or dihydromyricetin. Naringenin may possibly also be directly hydroxylated by F3’H or F3’5’H to deliver, respectively, eriodictyol and pentahydroxy-flavanone, that are once again hydroxylated to dihydroquercetin and dihydromyricetin. The three dihydroflavonols hence 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 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. Each of the colours above mentioned refer to a precise environmental situation, i.e., when the anthocyanidins are in an acidic compartment. The final frequent step for the production of coloured and stable compounds (anthocyanins) includes the glycosylation of cyanidin, pelargonidin and delphinidin by the enzyme UDP-glucose:flavonoid 3-O-glucosyl transferase (UFGT). Finally, only cyanidin-3-glucoside and delphinidin-3-glucoside could be additional methylated by methyltransferases (MTs), to be converted to peonidin-3-glucoside and petunidin- or malvidin-3-glucoside, respectively. The synthesis of PAs branches off the anthocyanin pathway just 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 happens by the addition of leucocyanidin molecules for the terminal unit of catechin or epicatechin, possibly catalysed by laccase-like polyphenol oxidases. However, the localization of those enzymes and their Carboxylesterase 1 Protein supplier actual substrates are still controversial [31,32].Int. J. Mol. Sci. 2013,Figure 1. (A) Scheme of your flavonoid biosynthetic pathway in plant cells. Anthocyanins are synthesized by a multienzyme complex loosely associated 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 actions missing in TARC/CCL17 Protein Gene ID grapevine. Numbers subsequent to the flavonoid groups are related to the chemical structures shown in (B). (B) Chemical structures in the big flavonoid groups.(A)(B)Int. J. Mol. Sci. 2013, 14 three. Mechanisms of Flavonoid Transport in Plant CellsIn the following section, recent advances on the models of flavonoid transport into vacuole/cell wall of distinctive plant species, ascribed to a general membrane transporter-mediated transport (MTT), will b.