Flavonoids synthesis

Flavonoids are the largest class of phenylpropanoids in plants. The basic flavonoid structure is two aromatic rings (one from phenylalanine and the other from the condensation of three malonic acids) linked by three carbons (Fig. 3.6). Chalcone is converted to naringenin by the enzyme chalcone isomerase, which is a key enzyme in flavonoid synthesis. This enzyme, like PAL and chalcone synthase (CHS), is under precise control and is inducible by both internal and external signals. Naringenin is the... 

TANAKA, A., TANO, S., CHANTES, T., YOKOTA, Y., SHIKAZONO, N., WATANABE, H., A new Arabidopsis mutant induced by ion beams affects flavonoid synthesis with spotted pigmentation in testa, Genes Genet. Syst., 1997, 72, 141-148. 

Regulation of Flavonoid Synthesis in C. americanum. Biosynthesis of methylated flavonol glucosides seems to be under tight regulation, not only by the substrate specificity of the enzymes involved, but also by other factors, among which are (a) the strict position specificity of these enzymes towards their hydroxylated or partially methylated substrates (b) the apparent difference in microenvironment of the different methyl-transferases, whereby those earlier in the pathway utilized aglycones whereas later enzymes accepted only glucosides as substrates (c) the subtle characteristic differences in methyl-transferases with respect to their pH optima, pi values and requirement for Mg ions, despite their similar molecular size ... 

Buer CS, Muday GK. 2004. The transparent testa4 mutation prevents flavonoids synthesis and alters auxin transport and the response of Arabidopsis roots for gravity and light. Plant Cell 16 1191-1205... 

Lozoya, E., Block, A., Lois, R., Hahlbrock, K. and Scheel, D. (1991) Transcriptional repression of light-induced flavonoid synthesis by elicitor treatment of cultured parsley cells. Plant., 1, 227-34. 

However, not all related species or conspecific populations respond similarly under the same UV influence. For example, Betula pendula and B. resinifera, two closely related birch species collected from populations in Europe and Alaska, generally produce a number of flavonoids, hydroxycinnamic acids, and condensed tannins in larger quantity in exposed leaves to artificial UV-B photon fluxes (4.9 kJ m d for 3 hr/day of biologically active radiation) than in non radiated plants (Lavola, 1997). In B. pendula populations the major increase was in flavonoid synthesis but in B. resinifera the bias was towards the hydroxycinnamic acids and condensed tannins. Besides, allopatric (geographically distant) populations of birch reacted differently in the synthesis of specific compounds. For example, chlorogenic acid increased by 22 and 92% in plants from Germany and Alaska, respectively, but in Finnish plants there was no increment at all. 

Keywords Adsorption Anthocyanins Flavonoid Synthesis Mutagenicity Proanthocyanidins... 

CYP71D subfamily is also large and currently comprises a total of 22 members from 10 different plant species. At present, the catalytic properties of five CYP71D enzymes have been determined and the enzymes assigned to specific steps in indole alkaloid, sequiterpenoid, cyclic terpenoid, and flavonoid synthesis. Accordingly, enzymes belonging to the CYP71D subfamily do not necessarily share similar functional characteristics. 

The Kinetic Model of Flavonoid Synthesis and Secretion ih PoDUlus (jl ds... 

Gerats, a. G. M, and C. Martin, Flavonoid synthesis in Petunia hybrida genetics and molecular biology of flower color, in Phenolic Metabolism in Plants (H. A. Stafford and R. K. Ibrahim, eds.). Recent Advances in Phytochemistry Vol. 26, 165-199, Plenum Press, New York, 1992. 

Two major groups of phenols exist that are formed by the sequential addition of C2 units to a growing chain. Acetyl-CoA is generally used as the primer in fungal systems, whereas a shikimic acid-derived acyl-CoA is required for flavonoid synthesis in higher plants. Flavonoids are multiringed phenols found most commonly in flowers and fruit, where they are responsible for the color. 

Tomato Maize/ overexpression E8 or CaMVd35S/LC + C7 Cl + LC MYB-type Cl and MYC-type LC are TFs required for production of anthocyanm in plants Induced flavonoid synthesis in fruit flesh Higher total flavonoids (10-fold) and total flavonol (20-fold) mainly kaempferol [79]... 

In plants, fatty acid synthase exists in plastids, so one function of the prokaryotic ACCase is to provide malonyl-CoA for de novo fatty acid synthesis. What is the role of the eukaryotic ACCase Malonyl-CoA is used for flavonoid synthesis. We examined effect of UV-B on the two ACCases in pea seedlings because various enzymes involved in flavonoid synthesis are induced by UV-B. 

Effects of UV-B irradiation on ACCase levels were examined for the primary leaves of 9-day-old seedlings. Nine-day-old seedlings were exposed to UV-B for 24 hr and the irradiated seedlings were returned to the earlier light conditions. The total proteins in the primary leaves were extracted and the biotinylated polypeptides were measured (Fig. 3). TTie levels of the ca. 220 kDa polypeptide increased after the irradiation, reached a maximum at one day after the irradiation started, and then decreased to a low level at two days after the irradiation stopped. The level of the ca. 35 kDa polypeptide changed little. In pea leaves, flavonoids and chalcone synthase are found in epidermis (9). The cytosolic ACCase is also abundant in epidermis (4). These results suggest that one function of the cytosolic ACCase is to supply malonyl-CoA for flavonoid synthesis. 

With such a limited data base, it is difficult to draw too many comparisons between flavonoid patterns in angiosperms vis-a-vis the gymnosperms. However, there is a general trend in flavonoid synthesis within the vascular plants toward... 

The second step in flavonoid synthesis is the isomerization of chalcone to flavanone, and the isomerase responsible has been isolated from parsley where... 

One of the last steps in flavonoid synthesis is methylation and an 0-methyl-transferase for this has been purified 82-fold from cell suspiension cultures of parsley. It has a pH optimum of 9.7, requires Mg, and the molecular weight is ca. 48000. Unlike catechol methylase from animal tissues, it is not inhibited by p-chloromercuribenzoate or by iodoacetamide. Luteolin (27) and its 7-glucoside were the best substrates, giving chrysoeriol (28) and its 7-gluco-side respectively K values were 4.6 x 10" and 3.1 x 10 moll Erio-dictyol and caffeic acid were poor substrates (K values 1.2 x 10 and 1.6 X 10 moll , respectively) and the enzyme was quite spteciflc for catechols and only 0-methylated a m-hydroxy-group. 

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