Biosynthesis of flavan-3-ols by leaf extracts of Onobrychis viciifolia

Singh, Sehijpal; McCallum, John; Gruber, Margaret Y.; Towers, G.H.N.; Muir, Alister D.; Bohm, Bruce A.; Koupai-Abyazani, Mohammed R.; Glass, Anthony D. M.

doi:10.1016/s0031-9422(96)00415-3

Cited by 30 publications

(21 citation statements)

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“…In the flavonoid pathway, the earliest step at which alternative 3-hydroxyl isomers might be formed is at the flavanone 3-hydroxylase enzyme step, when the 3-hydroxyl group is first incorporated to form dihydrokaempferol or dihydroquercetin. In a study of flavan-3-ol synthesis in extracts from leaves of O. viciifolia, Singh et al (1997) were able to demonstrate the synthesis of catechin and gallocatechin, but unable to demonstrate the synthesis of epicatechin or epigallocatechin from dihydroquercetin, even though O. viciifolia leaf polymers were composed of roughly 50% epigallocatechin and only 30% gallocatechin. They proposed that the (Ϫ) isomers are synthesized by an unspecified alternative route in the flavonoid pathway in O. viciifolia because there was no evidence for their direct synthesis nor an epimerase activity acting on (ϩ)-dihydroquercetin or its known products (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…The first committed step to PA biosynthesis, and the only one to be enzymically characterized, is catalyzed by the enzyme leucoanthocyanidin reductase (LAR). Reactions catalyzing the conversion of (ϩ)-3,4-cis-leucocyanidin to (ϩ)- gumes (Stafford and Lester, 1984;Tanner and Kristiansen, 1993;Singh et al, 1997;Skadhauge et al, 1997). PA is thought to be synthesized by sequential addition of an intermediate derived from a flavan-3,4-diol (e.g.…”

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Identification and Biochemical Characterization of Mutants in the Proanthocyanidin Pathway in Arabidopsis

et al. 2002

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Proanthocyanidin (PA), or condensed tannin, is a polymeric flavanol that accumulates in a number of tissues in a wide variety of plants. In Arabidopsis, we found that PA precursors (detected histochemically using OsO 4 ) accumulate in the endothelial cell layer of the seed coat from the two-terminal cell stage of embryo development onwards. To understand how PA is made, we screened mature seed pools of T-DNA-tagged Arabidopsis lines to identify mutants defective in the synthesis of PA and found six tds (tannin-deficient seed) complementation groups defective in PA synthesis. Mutations in these loci disrupt the amount (tds1, tds2, tds3, tds5, and tds6) or location and amount of PA (tds4) in the endothelial cell layer. The PA intermediate epicatechin has been identified in wild type and mutants tds1, tds2, tds3, and tds5 (which do not produce PA) and tds6 (6% of wild-type PA), whereas tds4 (2% of wild-type PA) produces an unidentified dimethylaminocinnamaldehyde-reacting compound, indicating that the mutations may be acting on genes beyond leucoanthocyanidin reductase, the first enzymatic reduction step dedicated to PA synthesis. Two other mutants were identified, an allele of tt7, which has a spotted pattern of PA deposition and produces only 8% of the wild-type level of type PA as propelargonidin, and an allele of tt8 producing no PA. Spotted patterns of PA deposition observed in seed of mutants tds4 and tt7-3 result from altered PA composition and distribution in the cell. Our mutant screen, which was not exhaustive, suggests that the cooperation of many genes is required for successful PA accumulation.Flavonoids are a diverse group of plant secondary metabolites that accumulate in a wide variety of plant tissues and include anthocyanins, flavonols, and the polymeric flavanols known as proanthocyanidins (PAs; Fig. 1). Like their flavanol constituents, PAs are rich in hydrophobic aromatic rings and hydroxyl groups that can interact with biological molecules, particularly proteins, by hydrogen bonds and hydrophobic interactions. Because PAs are polymeric, their interaction with proteins is much stronger than that of monomeric flavanols, presumably because of a "chelate" effect where polymeric PAs can interact with large proteins at multiple sites, increasing the strength of overall molecular interaction as well as minimizing dissociation of the complex once it is formed (Fersht, 1985). This strong interaction of PAs with proteins is probably the basis of their main role in plants and their uses by man.Because PA content of dietary plants can have both positive and negative effects on animal nutrition (Waghorn and Jones, 1989), an important agricultural objective is to manipulate the level of PA in pasture legumes (Morris and Robbins, 1997). When present in bloat-safe forage legumes, PA can bind to and cause the precipitation of dietary proteins, inhibiting the formation of stable proteinaceous foams, thereby preventing bloat (Tanner et al., 1995). Increasing the PA content of pastures such as alfalfa (Medicago s...

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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

Identification and Biochemical Characterization of Mutants in the Proanthocyanidin Pathway in Arabidopsis

et al. 2002

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“…A similar coupled assay with recombinant enzymes was shown to be essential for detection of LAR activity from L. corniculatus (Paolocci et al, 2007). A protein complex from Onobrychis viciifolia could produce catechin from dihydroflavonol (Singh et al, 1997), although the exact nature of the protein components was not reported. These observations are consistent with a recently proposed model for metabolic channeling in flavonoid biosynthesis, whereby PA-specific enzymes, such as LAR, ANS, and ANR, possibly along with DFR, might form a complex through which intermediates are channeled directly into the formation of PAs.…”

Section: Functional Characterization Of Mtlar and Mtans Through Modifmentioning

confidence: 99%

Early Steps in Proanthocyanidin Biosynthesis in the Model Legume Medicago truncatula

et al. 2007

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Oligomeric proanthocyanidins (PAs) composed primarily of epicatechin units accumulate in the seed coats of the model legume Medicago truncatula, reaching maximal levels at around 20 d after pollination. Genes encoding the single Medicago anthocyanidin synthase (ANS; EC 1.14.11.19) and leucoanthocyanidin reductase (LAR; EC 1.17.1.3) were cloned and the corresponding enzymes functionally identified. Recombinant MtANS converted leucocyanidin to cyanidin, and, more efficiently, dihydroquercetin to the flavonol quercetin. Levels of transcripts encoding dihydroflavonol reductase, ANS, and anthocyanidin reductase (ANR), the enzyme responsible for conversion of anthocyanidin to (−)-epicatechin, paralleled the accumulation of PAs in developing seeds, whereas LAR transcripts appeared to be more transiently expressed. LAR, ANS, and ANR proteins were localized to the cytosol in transfected tobacco (Nicotiana tabacum) leaves. Antisense down-regulation of ANS in M. truncatula resulted in reduced anthocyanin and PA levels, but had no impact on flavonol levels. Transgenic tobacco plants constitutively overexpressing MtLAR showed reduced anthocyanin content, but no catechin or increased levels of PAs were detected either in leaves or in flowers. Our results confirm previously ascribed in vivo functions for ANS and ANR. However, the apparent lack of catechin in M. truncatula PAs, the poor correlation between LAR expression and PA accumulation, and the lack of production of catechin monomers or oligomers in transgenic plants overexpressing MtLAR question the role of MtLAR in PA biosynthesis in Medicago.

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“…4, KoupaiAbyazani et al 1993b). The activities of four enzymes in the CT biosynthetic pathway (i.e., dihydroflavonol reductase, leucocyanidin reductase, leucodelphinidin reductase and chalcone synthase) are maximal in young, unexpanded leaves of sainfoin, and decline or are absent in older leaves (Singh et al 1997;Joseph et al 1998). Changes in CT content and chemical composition have implications with respect to the antinutritional qualities of the CT, since poly- For personal use only.…”

Section: Factors Affecting Condensed Tanninmentioning

confidence: 99%

A review of the effects of forage condensed tannins on ruminal fermentation and bloat in grazing cattle

McMahon¹,

McAllister²,

Berg³

et al. 2000

Can. J. Plant Sci.

239

178

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[469][470][471][472][473][474][475][476][477][478][479][480][481][482][483][484][485]. Condensed tannins (CT) are polyphenolic secondary plant products that are widespread in the plant kingdom. By definition, CT bind to protein and are regarded as "antinutritional" compounds which reduce protein digestibility. Variations in CT chemistry alter protein binding capacities among polymers from different plant species and developmental stages. Condensed tannins interact with proteins in feed, saliva and microbial cells, with microbial exoenzymes, and with endogenous proteins or other feed components, which alters digestive processes as compared with diets free of CT. Tannin levels exceeding 40 to 50 g kg -1 DM in forages may reduce protein and DM digestibility of the forages by ruminants. At low to moderate levels, CT increase the quantity of dietary protein, especially essential amino acids, flowing to the small intestine. Unlike alfalfa, legumes that contain CT do not cause bloat. Dietary CT may provide a means to beneficially manipulate protein digestion and/or prevent pasture bloat in ruminants. Research efforts are also currently being directed to genetically modify alfalfa to de-repress its CT biosynthetic pathway, or to move genes encoding steps of this pathway into alfalfa from other legumes. The effects of CT in forage legumes on digestion in ruminants and the potential use of tannin-rich forages for preventing bloat in grazing systems are discussed. Les tanins condensés (TC) sont des substances secondaires polyphénoliques répandues dans le règne végétal. Par essence fixés aux protéines, ils sont considérés comme substances antinutritionnelles qui réduisent la digestibilité des protéines. Leur constitution chimique, et par conséquent leur aptitude à se fixer aux protéines, fluctue selon la nature et le stade de croissance des espèces végétales. Les tanins condensés interagissent avec les protéines dans les aliments du bétail, dans la salive et dans les cellules microbiennes; avec les exoenzymes microbiens et avec les protéines endogènes ou avec d'autres composants des aliments du bétail, modifiant ainsi le processus de la digestion par rapport aux aliments sans TC. Des teneurs en tanins de plus de 40 à 50 g kg -1 m.s. dans les fourrages peuvent abaisser la digestibilité des protéines et de la matière sèche chez les ruminants. À des niveaux faibles à moyens, les TC accroissent le flux de protéines alimentaires, en particulier celui des acides aminés essentiels, vers l'intestin grêle. À la différence de la luzerne, les légumineuses qui contiennent des TC ne provoquent pas le météorisme. L'apport de TC dans l'alimentation des animaux peut être un moyen de manipuler positivement la digestion des protéines ou de prévenir le météorisme chez les ruminants au pâturage. Les recherches s'orientent également ves la modification génétique de la luzerne pour contrer l'inhibition de la biosynthèse des TC ou pour introduire dans l'espèce, à partir d'autres légumineuses, des gènes codant pour certaines étapes de cette voie....

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Biosynthesis of flavan-3-ols by leaf extracts of Onobrychis viciifolia

Cited by 30 publications

References 26 publications

Identification and Biochemical Characterization of Mutants in the Proanthocyanidin Pathway in Arabidopsis

Identification and Biochemical Characterization of Mutants in the Proanthocyanidin Pathway in Arabidopsis

Early Steps in Proanthocyanidin Biosynthesis in the Model Legume Medicago truncatula

A review of the effects of forage condensed tannins on ruminal fermentation and bloat in grazing cattle

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