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At least 19 recordsLinked to original sources
PubMed1995

Flavonol 3-O-glycosyltransferases associated with petunia pollen produce gametophyte-specific flavonol diglycosides.

Wild-type petunia pollen accumulates high levels of flavonol 3-O-glycosides. Pollen from conditionally male-fertile petunia has no flavonols and is unable to germinate. Pollen function is restored both in vivo and in vitro by providing flavonol aglycones, but not flavonol glycosides, to the pollen. In the present study, incubation of an in vitro suspension of conditionally male-fertile pollen with kaempferol or quercetin resulted in the accumulation of kaempferol and quercetin 3-O-glycosides in the pollen. We identified two glycosyltransferase activities associated with the intact pollen grain that catalyze the formation of a gametophyte-specific class of flavonol glycosides. Feeding studies showed that product formation was highly specific for flavonols with an unsubstituted 3-hydroxyl group and was not dependent on an external source of UDP-hexose. Ultraviolet spectral analysis, fast atom bombardment mass spectrometry, 1H-nuclear magnetic resonance, and 13C-nuclear magnetic resonance identified the products as kaempferol and quercetin 3-O-(2"- O-beta-D-glucopyranosyl)-beta-D-galactopyranoside, identical with the flavonol 3-O-glycosides present in wild-type pollen. The sugars are linked in a 1-->2 configuration that results in a pollen-specific class of compounds. To retain both glycosyltransferase activities in a cell-free extract, it was necessary to add triton X-100, suggesting that one or both of the proteins may be associated with a pollen membrane. A model for flavonol glycoside biosynthesis and uptake into the pollen is discussed in terms of the germination requirement for flavonols.

Carbohydrate Conformation↗
PubMed2005

Dietary flavonols and flavonol-rich foods intake and the risk of breast cancer.

Laboratory and animal studies suggest that dietary flavonols may reduce breast cancer risk but there are limited epidemiological studies. We computed flavonol intakes from dietary data collected by validated food frequency questionnaires in 1991 and 1995 from 90,630 women in the Nurses Health Study II. Using multivariate relative risks (RR) and 95% confidence intervals (95% CI), we evaluated the association of flavonol intake with breast cancer risk in women who were premenopausal and aged between 26 and 46 years at baseline in 1991. During 8 years of follow-up, we documented 710 cases of invasive breast cancer. The multivariate RR (95% CI), comparing highest to lowest quintiles of cumulative average intake, was 1.05 (0.83, 1.34; p-value for test of trend=0.96) for the sum of flavonols and there were no associations seen between individual flavonols such as kaempferol, quercetin and myricetin and breast cancer risk. The multivariate RR (95% CI), comparing highest to lowest quintiles of cumulative average intake, was 0.94 (0.72, 1.22; p-value for test of trend=0.54) for sum of flavonol-rich foods. Among the major food sources of flavonols, we found a significant inverse association with intake of beans or lentils but not with tea, onions, apples, string beans, broccoli, green pepper and blueberries. The multivariate RR (95% CI), comparing the highest category (2 or more times a week) of cumulative average beans or lentils intake with the lowest category (less than once a month), was 0.76 (0.57, 1.00; p-value for test of trend=0.03). While we found no overall association between intake of flavonols and risk of breast cancer, there was an inverse association with intake of beans or lentils that merits further evaluation.

Adult↗
PubMed2005

Isolation of five types of flavonol from seabuckthorn (Hippophae rhamnoides) and induction of apoptosis by some of the flavonols in human promyelotic leukemia HL-60 cells.

Five types of flavonol were isolated from seabuckthorn (Hippophae rhamnoides) and identified by mass, 1H- and 13C-NMR. The proliferations of human promyelotic leukemia HL-60 cells were inhibited as the concentrations of these flavonols were increased. The order of the extent of growth inhibition by the flavonols at a concentration of 20 microM is as follows: pentamethylquercetin > syringetin > isorhamnetin > quercetin > kaempherol > myricetin. Apoptotic morphological changes of the nucleus, including chromatin condensation were induced in the HL-60 cells treated with quercetin, kaempherol and myricetin, respectively, but not in the cells treated with the other flavonols. The fragmentations of DNA by quercetin, kaempherol and myricetin, respectively, to oligonucleosomal-sized fragments, a characteristic of apoptosis, were observed to be dose-dependent in the HL-60 cells. These findings suggest that growth inhibition by quercetin, kaempherol and myricetin, respectively, results from the induction of apoptosis by these flavonols. The other flavonols (pentamethylquercetin, syringetin and isorhamnetin) having methoxy (-OCH3) group inhibited more strongly than the above 3 flavonols without induction of apoptosis in the HL-60 cells. These findings suggest that mechanisms of growth inhibition by pentamethylquercetin, syringetin and isorhamnetin are different from the apoptosis caused by quercetin, kaempherol and myricetin.

Antineoplastic Agents↗
PubMed2006

Organ-specific transcription of putative flavonol synthase genes of grapevine and effects of plant hormones and shading on flavonol biosynthesis in grape berry skins.

In order to investigate the control mechanism of flavonol biosynthesis of grapevine, we obtained five genomic sequences (FLS1 to FLS5) of putative flavonol synthase genes from Vitis vinifera cv. Cabernet Sauvignon. The mRNA of five FLSs accumulated in flower buds and flowers, while the mRNA of FLS2, FLS4, and FLS5 accumulated in small berry skins and then decreased toward veraison. At the ripening stage, the mRNA of only FLS4 and FLS5 accumulated again. This change in mRNA accumulation did not contradict the flavonol accumulation in the berry skins. Shading of the berries completely inhibited the increase in flavonol content and mRNA accumulation of FLS4, but did not affect the mRNA accumulation of FLS5. The effects of light and plant hormones on flavonol accumulation were different from those on anthocyanin accumulation. Thus flavonol biosynthesis appears to be under a different control system from that of anthocyanin biosynthesis.

Amino Acid Sequence↗
PubMed1979

Mutagenicity of plant flavonols in the Salmonella/mammalian microsome test: activation of flavonol glycosides by mixed glycosidases from rat cecal bacteria and other sources.

Over 70 naturally occurring and synthetic flavonoids were screened for mutagenicity with 5 tester strains in the Salmonella/mammalian microsome assay: TA1535, TA100, TA1537, TA1538 and TA98. Frameshift mutagenicity was confined to the flavonols (flavon-3-ols) in strain TA98, TA1537 and TA100. The two most mutagenic falvonols, namely, quercetin (3,3',4',5,7-pentahydroxyflavone) and kaempferol (3,4',5,7-tetrahydroxyflavone), exhibiting 12 and 7 revertants/nmol in TA98 respectively, are also the most common flavonols occurring in plants. Other flavonols exhibited less activity (revertants/nmol): galangin (2.0), rhamnetin (0.45), kaempferide (0.24), fisetin (0.14), myricetin (0.12), robinetin (0.06) and morin (0.05). All of these flavonols apparently exhibited significant activation by Aroclor 1254 induced rat-liver microsome preparations (S9). However, subsequent study revealed that only those flavonols either lacking or possessing one B ring hydroxyl group had an absolute requirement for microsomal activation. Alternatively, quercetin with two B-ring OH groups is not activated by microsomal enzymes, but by soluble (S100) enzymes from liver which are apparently constitutive and not subject to the usual chemical induction. 3 flavonol glycosides, namely, quercetrin (quercetin-3-O-rhamnoside), rutin (quercetin-3-O-rutinoside) and robinin (kaempferol-3-O-galactosido-rhamnoside-7-O-rhamnoside), were found to be nonmutagenic. They could, however, be activated by a variety of mixed glycosidases incorporated in the usual pour plate procedure. The most effective enzyme mixtures were obtained from rat cecal bacteria and from the snail Helix pomatia.

Animals↗
PubMed1976

[Flavonols and flavones of vegetables. VI. On the changes of the flavonols of onions (authors transl)].

The epidermis of onion scales exclusively contains glucosides of quercetin as flavonols, while the dry outer skins contain quercetin in the free state mainly. First spiraeoside (quercetin-4'-glucoside) is built; the formation of diglucosides follows during storage and increases continously. The mesophyll appears to be free of flavonols. The flavonol concentration decreases from the outer to the inner scales, with higher levels in the outer than in the inner epidermis. In the green leaves the flavonol synthesis is light-dependent and also kaempferol glucosides are formed beside quercetin glucosides, but not spiraeoside and the known diglucosides of the scales. During drying on the field an accumulation of flavonols takes place in the drying leaves. This production is associated with the formation of free quercetin and spiraeoside, but not of free kaempferol.

Flavonoids↗
PubMed2000

HPLC separation of flavonols, flavones and oxidized flavonols with UV-, DAD-, electrochemical and ESI-ion trap MS detection.

The cation-induced or electrochemical oxidation of flavonols has been reported to yield 2-(hydroxybenzoyl)-2-hydroxy-3(2H)-benzofuranone. Two new gradient reversed phase HPLC methods are presented which allow the determination of those oxidized flavonols simultaneously with flavonols and flavones. UV and electrochemical detection are used because of their high sensitivity. Qualitative detection together with quantification of all compounds is achieved with photodiode-array detection. An electrospray ionization ion trap mass spectrometric method is presented for unique identification of the benzofuranones after HPLC separation.

Chromatography, High Pressure Liquid↗
PubMed1985

Enzymatic synthesis of polymethylated flavonols in Chrysosplenium americanum. I. Partial purification and some properties of S-adenosyl-L-methionine:flavonol 3-, 6-, 7-, and 4'-O-methyltransferases.

Four novel flavonol O-methyltransferases (OMTs) were partially purified from Chrysosplenium americanum by precipitation with ammonium sulfate, successive chromatography on Sephacryl S-200 and hydroxylapatite, and chromatofocusing on Polybuffer ion exchanger. They exhibited strict position specificity for positions 3 of quercetin, 7 of 3-methylquercetin, 4' of 3,7-dimethylquercetin, and 6 of 3,7,3'-trimethylquercetagetin. None of these enzymes reacted with phenylpropanoids, flavones, dihydroflavonols, or any of their glucosides. Except for the 7-OMT whose activity was lost during chromatofocusing, the other enzymes had apparent pI values of 4.8, 5.4, and 5.7 for the 3-, 4'-, and 6-OMTs, respectively. They had similar molecular weights (Mr 57,000) and their pH optima varied between 7.8 and 9.0, with a shift in optimal activity from lower to higher pH with increasing level of substrate methylation. Unlike the 3 and 4' enzymes, the 6-OMT showed an absolute requirement for Mg2+ whose activation was saturable and was inhibited by EDTA. The in vitro stepwise O-methylation of quercetin----3-methylquercetin----3,7-dimethylquercetin----3 ,7, 4'-trimethylquercetin tends to suggest a coordinated sequence of methyl transfers in this tissue.

Cations, Divalent↗
PubMed1975

[Flavonols and flavones of vegetables. V. Flavonols and flavones of root vegetables (author's transl)].

Root vegetables contain flavon(ol) glycosides in tracers up to small amounts, while the level of their leaves are in part considerable (to more than 1 g/kg, calculated as aglycon). Radish, rutabagas, scorzoneras, and beets contain less than 1 mg/kg kaempferol and/or quercetin; carrots less than 1 mg/kg apigenin and luteolin; celery roots ca. 75 mg apigenin/kg and 14 mg luteolin/kg; horseradish about 20 mg kaempferol/kg and small radish 1-10 mg kaempferol/kg, whereby all these flavones and flavonols occur as glycosides in the vegetables. In leaves of small radish, variety "Eiszapfen", we found besides isoquercitrin (quercetin-3-glucoside) a quercetin-3-0-diglycoside and a kaempferol-0-diglycoside, both with the sugars rhamnose and arabinose, by tlc.

Arabinose↗
PubMed1985

Enzymatic synthesis of polymethylated flavonols in Chrysosplenium americanum. II. Substrate interaction and product inhibition studies of flavonol 3-, 6-, and 4'-O-methyltransferases.

The steady-state kinetic behavior of three position-specific O-methyltransferases (3-, 4'-, and 6-OMTs) was compared with reference to substrate inhibition patterns in Chrysosplenium americanum. The 6-OMT was severely inhibited by the flavonoid substrate at concentrations close to Km, whereas the other two enzymes were less affected by their respective flavonoid substrates. Substrate interaction kinetics for the 6-OMT gave converging lines consistent with a sequential binding mechanism, whereas the data generated for the 3- and 4'-OMTs could be fitted to the equation for a ping-pong mechanism or to that of a sequential binding mechanism where Kia was much smaller Ka. More information on the mechanism of reaction was obtained from product inhibition studies. The three enzymes exhibited competitive inhibition patterns between S-adenosyl-L-methionine (SAM) and S-adenosyl-L-homocysteine (SAH), whereas other patterns were either noncompetitive or uncompetitive. The steady-state kinetic properties of the 3-, 4'-, and 6-OMTs were consistent with a sequential ordered reaction mechanism, in which SAM and SAH were leading reaction partners and included an abortive EQB complex. Product inhibition constants were sufficiently low to suggest that these may be important in regulating the pathway of polymethylated flavonoid synthesis. It was suggested that due to their greater sensitivity to inhibition by SAH, the OMTs involved in earlier steps of the methylation sequence may regulate the rate of synthesis of final products in Chrysosplenium.

Flavonoids↗
PubMed1976

[Flavonols and flavones of vegetables. VII. Flavonols of leek, chive and garlic (author's transl)].

Green leaves of leek and chive mainly contain kaempferol glycosides, with mono- and di-glycosides dominating in leek and di- and tri-glycosides in chive. In leek glucose is dominant as sugar component compared to xylose; in chive we found glucose and galactose. Kaempferol-3-beta-D-glucoside and kaempferol-3-xylosyl-beta-D-glucoside were isolated from leek and the 3-beta-D-glucosides of kaempferol, quercetin and isorhamnetin as by-glycosides from chive. In leek traces of quercetin-3-glucoside were identified by tlc, but no spiraeoside (quercetin-4'-glucoside) could be detected in the two species. The bulbs of garlic and leek contain only few milligram of glycosides of kaempferol and quercetin per kg fresh weight.

Flavonoids↗
PubMed1998

[Flavonols, flavone and anthocyanins as natural antioxidants of food and their possible role in the prevention of chronic diseases].

Flavonoids are non-nutritive compounds of plants that have been intensively investigated during the past years due to their possible protective effects against chronic diseases. In vitro studies were able to demonstrate for flavonols, flavones, and most recently also for anthocyanins a considerable antioxidative activity, mainly based on scavenging of oxygen radicals. Flavonols and anthocyanins are commonly found in European fruits and vegetables. In addition, black tea and red wine may have a high content of these compounds. Those food items are the main sources of flavonol consumption each contributing to a different degree to the overall intake. The absorption of aglycones has been established before. However, only recently could the absorption of flavonolglycosides be demonstrated. The mean intake of flavonols of the German population was calculated using data from the National German Food Consumption Survey. According to this analysis, the daily per capita intake was about 11.5 mg flavonols, mainly derived from fruits and vegetables, but also from black tea and red wine. Epidemiological studies have been directed to investigate the association between flavonol consumption and diseae risk. An inverse association between flavonol intake and mortality from myocardial infarction was observed. According to one of three studies, the flavonoid intake can be inversely correlated with cancer risk. This review summarizes the current knowledge on the occurrence, intake, bioavailability, and antioxidative properties of flavonols, flavones, and anthocyanins as well as the associations between flavonol intake and disease risks. Possible health related effects especially of flavonols are critically reflected, and the necessity of further research in outlined.

Anthocyanins↗
PubMed1997

Regulation of flavonol biosynthesis during anther and pistil development, and during pollen tube growth in Solanum tuberosum.

The regulation of flavonol biosynthesis was studied in anthers and pistils of Solanum tuberosum. Flavonols are essential for functional pollen tube growth in a number of species. Flavonol accumulation in whole anthers started at the unicellular stage of pollen development and continued until pollen maturity. A cDNA clone encoding flavonol synthase (FLS) was isolated. Fls gene expression was detected in pistils, anthers, petals and ovaries, the organs in which flavonols are accumulating. Fls transcripts were present in unicellular and bicellular pollen, but not in mature pollen. The expression patterns of three genes encoding enzymes in the flavonoid biosynthetic pathway, chalcone synthase (chs), flavanone-3-hydroxylase and fls were analysed in developing anthers and pistils. Only chs transcripts accumulated concomitantly with the flavonols in anthers. In pistils of potato, pollen tube growth induced an increase in fls gene expression that, unlike the situation in pollinated pistils of petunia, did not result in an increased flavonol content. Flavonol biosynthesis in anthers is probably initiated by the expression of the chs gene, and flavonol accumulation in pistils upon pollen tube growth is not an universal phenomenon.

Acyltransferases↗
PubMed2000

Antioxidant flavonols from fruits, vegetables and beverages: measurements and bioavailability.

Flavonols are polyphenolic secondary plant metabolites that are present in varying levels in commonly consumed fruits, vegetables and beverages. Flavonols have long held an interest for nutritionists, which has increased following a Dutch study in the early 1990's showing that dietary intake of flavonols was inversely correlated with the incidence of coronary heart disease. The main factors that have hindered workers in the field of flavonol research are (i) the accurate measurement of these compounds in foods and biological samples, and (ii) a dearth of information on their absorption and metabolism. This review aims to highlight the work of the authors in attempting to clarify the situation. The sensitive and selective HPLC procedure to identify and quantify common flavonols and their sugar conjugates is described. In addition, the results of an on-going screening program into the flavonol content of common produce and beverages are presented. The bioavailability of dietary flavonols is discussed with reference to an intervention study with onions, as well as pilot studies with tea, red wine and cherry tomatoes. It is concluded that flavonols are absorbable and accumulate in plasma and that consuming high flavonol-containing varieties of fruits and vegetables and particular types of beverages could increase their circulatory levels.

Antioxidants↗
PubMed2001

Overexpression of petunia chalcone isomerase in tomato results in fruit containing increased levels of flavonols.

Tomatoes are an excellent source of the carotenoid lycopene, a compound that is thought to be protective against prostate cancer. They also contain small amounts of flavonoids in their peel ( approximately 5-10 mg/kg fresh weight), mainly naringenin chalcone and the flavonol rutin, a quercetin glycoside. Flavonols are very potent antioxidants, and an increasing body of epidemiological data suggests that high flavonoid intake is correlated with a decreased risk for cardiovascular disease. We have upregulated flavonol biosynthesis in the tomato in order to generate fruit with increased antioxidant capacity and a wider range of potential health benefit properties. This involved transformation of tomato with the Petunia chi-a gene encoding chalcone isomerase. Resulting transgenic tomato lines produced an increase of up to 78 fold in fruit peel flavonols, mainly due to an accumulation of rutin. No gross phenotypical differences were observed between high-flavonol transgenic and control lines. The phenotype segregated with the transgene and demonstrated a stable inheritance pattern over four subsequent generations tested thus far. Whole-fruit flavonol levels in the best of these lines are similar to those found in onions, a crop with naturally high levels of flavonol compounds. Processing of high-flavonol tomatoes demonstrated that 65% of flavonols present in the fresh fruit were retained in the processed paste, supporting their potential as raw materials for tomato-based functional food products.

Chalcone↗
PubMed1999

Purification, cloning, and heterologous expression of a catalytically efficient flavonol 3-O-galactosyltransferase expressed in the male gametophyte of Petunia hybrida.

Flavonols are plant-specific molecules that are required for pollen germination in maize and petunia. They exist in planta as both the aglycone and glycosyl conjugates. We identified a flavonol 3-O-galactosyltransferase (F3GalTase) that is expressed exclusively in the male gametophyte and controls the formation of a pollen-specific class of glycosylated flavonols. Thus an essential step to understanding flavonol-induced germination is the characterization of F3GalTase. Amino acid sequences of three peptide fragments of F3GalTase purified from petunia pollen were used to isolate a full-length cDNA clone. RNA gel blot analysis and enzyme assays confirmed that F3GalTase expression is restricted to pollen. Heterologous expression of the F3GalTase cDNA in Escherichia coli yielded active recombinant enzyme (rF3GalTase) which had the identical substrate specificity as the native enzyme. Unlike the relatively nonspecific substrate usage of flavonoid glycosyltransferases from sporophytic tissues, F3GalTase uses only UDP-galactose and flavonols to catalyze the formation of flavonol 3-O-galactosides. Kinetic analysis showed that the k(cat)/K(m) values of rF3GalTase, using kaempferol and quercetin as substrates, approaches that of a catalytically perfect enzyme. rF3GalTase catalyzes the reverse reaction, generation of flavonols from UDP and flavonol 3-O-galactosides, almost as efficiently as the forward reaction. The biochemical characteristics of F3GalTase are discussed in the context of a role in flavonol-induced pollen germination.

Amino Acid Sequence↗