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PubMed2002

Chalcones and flavonoids as anti-tuberculosis agents.

A series of flavonoids, chalcones and chalcone-like compounds were evaluated for inhibitory activity against Mycobacterium tuberculosis H37Rv. Among them, eight compounds exhibited >90% inhibition on the growth of the bacteria at a concentration of 12.5 microg/mL. Chalcones 1-(2-hydroxyphenyl)-3-(3-chlorophenyl)-2-propen-1-one (22) and 1-(2-hydroxyphenyl)-3-(3-iodophenyl)-2-propen-1-one (37) demonstrated 90 and 92% inhibition, respectively. Chalcone-like compounds (heterocyclic ring-substituted 2-propen-1-one) 1-(4-fluorophenyl)-3-(pyridin-3-yl)-2-propen-1-one (48), 1-(3-hydroxyphenyl)-3-(phenanthren-9-yl)-2-propen-1-one (49), 1-(pyridin-3-yl)-3-(phenanthen-9-yl)-2-propen-1-one (50) and 1-(furan-2-yl)-3-phenyl-2-propen-1-one (51) exhibited 98, 97, 96 and 96% inhibition, respectively. The actual minimum inhibitory concentrations (MIC), defined as the lowest concentration inhibiting 99% of the inoculum, for 22, 37, 48, 49, 50 and 51 were 20.3, 31.5, 48.3, >35.7, 6.8 and 19.2, respectively. A hydrophobic substituent on one aromatic ring, and a hydrogen-bonding group on the other aromatic ring resulted in increased anti-TB activity of the chalcones and chalcone-like compounds. Flavones and flavanones are more geometrically constrained than the corresponding chalcone analogues. The decreased activity of the flavones with respect to the chalcones may be due to the confinement of the terminal aromatic rings to the same plane.

Antitubercular Agents↗

PubMed2004

First bacterial chalcone isomerase isolated from Eubacterium ramulus.

The human fecal anaerobe Eubacterium ramulus is capable of degrading various flavonoids, including the flavone naringenin. The first step in the proposed degradation pathway is the isomerization of naringenin to the corresponding chalcone. Cell-free extracts of E. ramulus displayed chalcone isomerase activity. The enzyme from E. ramulus was purified to homogeneity. Its apparent molecular mass was estimated to be 136 and 129 kDa according to gel filtration and native polyacrylamide gel electrophoresis, respectively. Chalcone isomerase is composed of one type of subunit of 30 kDa. The purified enzyme catalyzed the isomerization of naringenin chalcone, isoliquiritigenin, and butein, three chalcones that differ in their hydroxylation pattern. N-bromosuccinimide, but also naringenin and phloretin, inhibited the purified enzyme considerably. This is the first report on a bacterial chalcone isomerase. The physiological function of the purified enzyme is unclear, but an involvement in the conversion of the flavanone naringenin to the chalcone is proposed.

Bromosuccinimide↗

PubMed2006

New administration model of trans-chalcone biodegradable polymers for the treatment of experimental leishmaniasis.

The present study was designed to investigate a new administration model and the antileishmanial activity of a semi-synthetic chalcone, benzylideneacetophenone (trans-chalcone). The antileishmanial activity of this product was first tested in vitro against promastigotes of L. braziliensis, L. tropica, L. infantum and L. amazonensis. An in vivo experiment was carried out using subcutaneous administration of trans-chalcone and implants of synthetic biodegradable polymers, polylactic acid (PLA) and polylactic/glycolic acid (PLGA). This compound showed potent inhibitory effects on the growth of all Leishmania strains examinated. Subcutaneous administration of trans-chalcone at a single dose of 4 mg/kg of body weight reduced lesion development in mice infected with L. amazonensis. A similar inhibition of the lesion growth in mice treated with trans-chalcone and pentamidine was observed. PLA and PGLA implants of trans-chalcone at 4 mg/kg were administered to mice infected with L. amazonensis. PLGA implants induced a highest reduction in the lesion size (31.25%) than PLA implants (10.75%). Treatment in vitro with trans-chalcone at IC50, completely inhibited the pathogenicity of this parasite in vivo. The development of this model provides a new practical technique for delivering drugs and can be useful for experimental leishmaniasis treatment.

Absorbable Implants↗

PubMed2005

Chalcone inhibits the proliferation of human breast cancer cell by blocking cell cycle progression and inducing apoptosis.

Chalcones are discussed to represent cancer preventive food components in a human diet that is rich in fruits and vegetables. In this study, we examined chalcone (1,3-diphenyl-2-propenone) for its effect on proliferation in human breast cancer cell lines, MCF-7 and MDA-MB-231. The results showed that chalcone inhibited the proliferation of MCF-7 and MDA-MB-231 by inducing apoptosis and blocking cell cycle progression in the G2/M phase. Immunoblot assay showed that chalcone significantly decreased the expression of cyclin B1, cyclin A and Cdc2 protein, as well as increased the expression of p21 and p27 in a p53-independent manner, contributing to cell cycle arrest. An enhancement in Fas/APO-1 and its two form ligands, membrane-bound Fas ligand (mFasL) and soluble Fas ligand (sFasL), was responsible for the apoptotic effect induced by chalcone. In addition, chalcone also triggered the mitochondrial apoptotic signaling by increasing the amount of Bax and Bak and reducing the level of Bcl-2 and Bcl-X(L), and subsequently activated caspase-9 in MCF-7 and MDA-MB-231 cells. Taken together, our study suggests that the blockade of cell cycle progression and initiation of cell apoptotic system may participate in the antiproliferative activity of chalcone in human breast cancer cells.

Antineoplastic Agents↗

PubMed1999

The antileishmanial activity of novel oxygenated chalcones and their mechanism of action.

Our previous studies have shown that licochalcone A, an oxygenated chalcone, has antileishmanial and antimalarial activities, and alters the ultrastructure and function of the mitochondria of Leishmania spp. parasites. The present study was designed to investigate the antileishmanial activity and the mechanism of action of a group of new oxygenated chalcones. The tested oxygenated chalcones inhibited the in-vitro growth of Leishmania major promastigotes and Leishmania donovani amastigotes. Treatment of hamsters infected with L. donovani with intraperitoneal administration of two oxygenated chalcones resulted in a significant reduction of parasite load in the liver and the spleen compared with untreated control animals. The oxygenated chalcones also inhibited the respiration of the parasite and the activity of mitochondrial dehydrogenases. Electron microscopic studies illustrated that they altered the ultrastructure of the mitochondria of L. major promastigote. The data clearly indicate that this group of oxygenated chalcones has a strong antileishmanial activity and might be developed into a new antileishmanial drug. The antileishmanial activity of oxygenated chalcones might be the result of interference with function of the parasite mitochondria.

Animals↗

PubMed1980

Genetic control of chalcone isomerase activity in flowers of Dianthus caryophyllus.

In flowers of Dianthus caryophyllus (carnation), the gene I is concerned with a discrete step in flavonoid biosynthesis, Genotypes with recessive (ii) alleles produce yellow flowers, which contain the chalcone isosalipurposide (naringenin-chalcone-2'-glucoside) as the major petal pigment, but in genotypes with wild-type alleles flavonols and anthocyanins can be formed and the flowers are white or red. Enzymatic measurements on petal extracts of four strains with different flower coloration revealed a clear correlation between accumulation of chalcone in recessive genotypes and deficiency of chalcone isomerase (E.C. 5.5.1.6) activity. From the chemogenetic and enzymological evidence it can be concluded that naringenin-chalcone is the first product of the synthesis of the flavonoid skeleton and that only the conversion of naringenin-chalcone to naringenin furnishes the substrate for the further reactions to flavonol and anthocyanin.

Chalcone↗

PubMed2005

Antifungal activity and studies on mode of action of novel xanthoxyline-derived chalcones.

Chalcones and chalcone-like compounds, most of them new ones, prepared by base-catalyzed condensation of appropriate aldehydes and xanthoxyline, were tested for antifungal properties against a panel of yeasts, hialohyphomycetes as well as dermatophytes with the agar dilution assay. Results indicate that neither the sole presence of a "xanthoxyline-like" substitution pattern nor a 2'-OH substituent on ring A are sufficient for these compounds to have antifungal properties. The chalcone 3-(2-chlorophenyl)-1-(2'-hydroxy-4',6'-dimethoxyphenyl)prop-2-en-1-one, with a Cl atom in the ortho position of benzene ring B showed the best antifungal activity against standardized strains of Trichophyton rubrum (MIC = 12.5 microg/mL) and inhibited all of the ten clinical isolates of T. rubrum tested (MIC at which 50 % [MIC(50)] and 90 % [MIC(90)] of the isolates were inhibited = 12.5 and 25 microg/mL). Regarding its mode of action, the Neurospora crassa assay showed a blotchy appearance in the inhibition halo produced by this chalcone, strongly suggesting that it could act by inhibiting the fungal cell wall. This chalcone seems to be an hyphal malformation inducer, since a clear curling of the hypha was observed in this hazy zone at a magnification of x 400. This work strongly contributes to the knowledge of the antifungal properties of hydroxy-chalcones.

Acetophenones↗

PubMed2000

In vitro evaluation of newly developed chalcone analogues in human cancer cells.

PURPOSE: Among flavonoids, chalcones have been identified as interesting compounds having chemopreventive and antitumor properties. We studied a panel of newly developed chalcone analogues (S1-S10) using MDA-MB 231 and MCF-7 ADRr breast cancer cells and the T-leukemic Jurkat cell line. Quercetin was used as the reference compound. METHODS: Antiproliferative activity was evaluated by cell counts performed after 72 h of exposure to the drugs. DNA analysis and redox activity were evaluated using flow cytometry. Apoptosis was assessed by morphological analysis, using YOYO-1 as DNA dye; p-glycoprotein function was ascertained by quantitating the efflux of rhodamine 123. RESULTS: All cells were sensitive to chalcone analogues yielding IC50 in micromolar concentrations with the following order regardless of the multidrug resistance (MDR) status: S1 > S2 > quercetin. S1 and S2, the most active compounds, were selected to evaluate their effect on the cell cycle, apoptosis, redox activity, and modulation of the p-glycoprotein function. No significant perturbation in cell cycle was seen with concentration up to 1 microM after 24 h. After 72 h a slight increase in G2/M block and DNA fragmentation occurred at 10 microM. Morphological analysis of apoptosis showed that chalcone analogues induced apoptosis to a higher extent than quercetin. Redox analysis demonstrated that all substances were able to increase intracellular thiol levels, which returned to baseline value after 24 h for all drugs except quercetin. Production of reactive oxygen species was essentially unaffected by all compounds. Finally, in MDR-positive MCF-7 ADRr cells chalcone analogues were unable to modulate p-glycoprotein function while quercetin was able to. CONCLUSIONS: Newly developed S1 and S2 chalcones have a different but higher antitumor activity than quercetin and could be considered as potential new anticancer drugs.

ATP Binding Cassette Transporter, Subfamily B↗

PubMed1985

Effects of chalcone derivatives on lipoxygenase and cyclooxygenase activities of mouse epidermis.

The effects of chalcone derivatives on 12-lipoxygenase and cyclooxygenase of mouse epidermis were investigated. The chalcone derivatives which have 3,4-dihydroxycinnamoyl structure in the molecule, such as 3,4-dihydroxychalcone, 3,4,2'-trihydroxychalcone, 3,4,4'-trihydroxychalcone and 3,4,2'4'-tetrahydroxychalcone, potently inhibited epidermal 12-lipoxygenase activity. Although some of them also inhibited cyclooxygenase activity at relatively high concentrations, the inhibitory effects of these chalcone derivatives on 12-lipoxygenase were 10 times or more potent than their effects on cyclooxygenase. The chalcone derivatives which have cinnamoyl or 4-hydroxycinnamoyl structure, instead of 3,4-dihydroxycinnamoyl structure, in the molecule, showed little or no inhibitory effects on either 12-lipoxygenase or cyclooxygenase activities. The inhibitory effects of chalcone derivatives on 12-lipoxygenase and cyclooxygenase of mouse epidermis are dependent on the particular structure, i.e. 3,4-dihydroxycinnamoyl structure, of the chalcone derivatives.

Animals↗

PubMed1994

Inhibition of carcinogen-induced pulmonary and mammary carcinogenesis by chalcone administered subsequent to carcinogen exposure.

A study of the capacity of chalcone to inhibit benzo[alpha]pyrene(BP)-induced carcinogenesis of the lungs and forestomach in female A/J mice and N-methyl-N-nitrosourea (MNU)-induced mammary carcinogenesis in female Sprague-Dawley rats has been carried out. Chalcone, 5 mg/g of diet, had a inhibitory effect on pulmonary adenoma formation (29%) and on mammary tumor formation (49%) when the compound was fed starting one week after final carcinogen administration. Chalcone did not inhibit forestomach tumor formation. In an additional study, chalcone started 4 weeks after MNU and fed for 3-week courses alternating with 3-week courses of control diet for the duration of the protocol also inhibited mammary tumor formation by 49%. The data showing that chalcone has inhibitory effects against both pulmonary and mammary carcinogenesis when given after carcinogen administration provides the basis for further investigations of this and possibly other chalcones as chemopreventive suppressing agents.

Adenoma↗

PubMed2005

Chemoprotective and toxic potentials of synthetic and natural chalcones and dihydrochalcones in vitro.

Cytochrome P4501A activity, oxidative stress and inhibition of gap junctional intercellular communication (GJIC) are involved in metabolic activation of promutagens and tumor-promoting activity of various xenobiotics, and their prevention is considered to be an important characteristic of chemoprotective compounds. In this study, a series of 31 chalcones and their corresponding dihydroderivatives, substituted in 2,2'-, 3,3'-, 4- or 4'-position by hydroxyl or methoxy group, were tested for their ability to inhibit Fe(II)/NADPH-enhanced lipid peroxidation and cytochrome P4501A-dependent 7-cethoxyresorufin-O-deethylase (EROD) activity in rat hepatic microsomes. Effects of the compounds on GJIC were determined in rat liver epithelial WB-F344 cells. Most of the chalcones and dihydrochalcones inhibited EROD activity in a dose-dependent manner at the range 0.25-25 microM, which was comparable to model flavonoid inhibitors alpha-naphthoflavone and quercetin. The chalcones exhibited higher inhibition activity than the corresponding dihydroderivatives. Mono and dihydroxylated chalcones, and dihydrochalcones showed none or only a weak antioxidant activity; trihydroxyderivatives inhibited in vitro lipid peroxidation significantly only at 50 microM concentration. Potential adverse effects, namely inhibition of GJIC and/or cytotoxicity were detected after treatment of WB-F344 cells with a number of chalcone and dihydrochalcone derivatives, suggesting that they should be excluded from additional screening as chemoprotective compounds. Chalcones and dihydrochalcones substituted at 4- and/or 4'-position, which elicited no inhibition of GJIC, were further tested for the potential enhancing effects on GJIC. The present data seem to suggest that 4-hydroxy, 2',4'-dihydroxy-3-methoxy, 2,4,4'-trihydroxy, and 2',4,4'-trihydroxychalcone, 2',4-dihydroxy and 2'-hydroxy-3,4-dimethoxydihydrochalcone might be promising chemoprotective compounds against CYP1A activity, and partly also against oxidative damage without inducing adverse effects, such as GJIC inhibition. In general, determination of potencies of tested compounds to inhibit GJIC should be involved in any set of methods for the in vitro screening of chemoprotective characteristics of potential drugs, in order to reveal their potential adverse effects associated with tumor promotion.

Animals↗

PubMed1997

Synthesis and structure-activity relationships of carboxylated chalcones: a novel series of CysLT1 (LTD4) receptor antagonists.

The synthesis and CysLT1 antagonistic activities of a new series of 2-, 3-, and 4-(2-quinolinylmethoxy)- and 3- and 4-[2-(2-quinolinyl)ethenyl]-substituted, 2'-, 3'-, 4'-, or 5'-carboxylated chalcones are described. Structure-activity relationship studies indicate a preference for the presence of a negatively charged (acidic) moiety, although in some cases nitrile or ester analogues also exhibit moderate activity. The quinoline moiety may be substituted at either the 3- or the 4-position. Replacement of this heterocycle by other aromatic groups results in compounds with comparable affinities [2-(7-chloroquinoline), 1-(1-methyl-2-benzimidazole), or 1-(2-benzothiazole)] or substantially lower activities [1-(1-ethoxyethyl)-2-benzimidazole, 2-naphthyl, or phenyl]. The quinoline and chalcone moieties may be connected by either an ethenyl or a methoxy spacer. The acidic moiety at the chalcone B ring may be attached to the 2'-, 3'-, 4'-, or 5'-position, for both the 3- and 4-substituted chalcones. There are no general patterns to specify which substitution positions gave the most potent compounds. The series contains several potent CysLT1 receptor antagonists, with K(D) values approaching the nanomolar range, as measured by the displacement of [3H]LTD4 from guinea pig lung membranes. Antagonism of LTD4-induced contraction of guinea pig ileum, the inhibition of antigen-induced contraction of guinea pig trachea in vitro, and the inhibition of LTD4-induced increase of vascular permeability in vivo are determined for chalcones with high CysLT1 receptor affinities (K(D) values below 0.1 microM). 2'-Hydroxy-4-(2-quinolinylmethoxy)-5'-(5-tetrazolyl)chalcone (14, VUF 4819) showed good activity in both in vitro and in vivo assays and has been selected for further evaluation.

Animals↗

PubMed2006

Chalcone inhibition of anthracycline secondary alcohol metabolite formation in rabbit and human heart cytosol.

Antineoplastic therapy with anthracyclines like doxorubicin (DOX) and daunorubicin (DNR) is limited by the possible development of a dose-related cardiomyopathy. Secondary alcohol metabolites like doxorubicinol (DOXol) and daunorubicinol (DNRol), formed by cytoplasmic two-electron reductases, have been implicated as potential mediators of anthracycline-induced cardiomyopathy. In the present study, we characterized the effects of 12 chalcones on the formation of anthracycline secondary alcohol metabolites by rabbit or human heart cytosol and compared them with those of quercetin and other flavonoids. Both chalcones and flavonoids inhibited DOXol or DNRol formation in isolated rabbit heart cytosol. Structure--activity relationships showed that inhibition by chalcones was determined primarily by the position of hydroxyl groups in their phenolic A and B rings. In particular, the presence of a hydroxyl group at C-4' in the A ring was an important determinant of the inhibitory activity of chalcones. Among chalcones, 2',4',2-trihydroxychalcone exhibited the highest inhibition of both DOXol and DRNol formation, but it proved less efficient than quercetin. Different results were obtained with isolated human heart cytosol: in the latter, 2',4',2-trihydroxychalcone and other hydroxychalcones inhibited both DOXol and DNRol formation, whereas quercetin and other flavonoids inhibited DNRol formation but failed to inhibit or slightly stimulated DOXol formation. These results identify chalcones as versatile inhibitors of the cytoplasmic reductases that convert anthracyclines to cardiotoxic secondary alcohol metabolites.

Adult↗

PubMed1997

Tumor cell growth suppression by chalcone (1,3-diphenyl-2-propen-1-one).

Chalcone or 1,3-diphenyl-2-propen-1-one which is widely distributed in higher plants and is considered to be a precursor of all flavonoids, was studies in terms of its anti-tumor growth activity in vitro and in vivo. Mice given the chalcone, which was suspended in the drinking water, showed a statistically significant rise in percent survival: 66% at the 35th day for the chalcone-treated animals vs. 30% for the control ones. The chalcone also gave significant suppression of growth of HCT-15 and Meth/A cells in vitro. The dose of 50% reduction in growth was between 2.5 micrograms/ml and 0.6 microgram/ml for the HCT-15 cells and less than 10 micrograms/ml for the Meth/A cells. Histograms obtained by flow cytometric examination showed an elevated region between the diploid and the tetra-ploid nucleoidal peaks. A third peak heavier than the tetra-ploid peak was also observed, which peak was not observed in the control. The percentage of cells in the S phase was significantly raised. Microscopically, large nucleated cells were observed following addition of the chalcone. These results suggest that the chalcone induced abnormal DNA synthesis and mitosis in the cultured cells.

Animals↗

PubMed2005

In vitro antiplasmodial activity of prenylated chalcone derivatives of hops (Humulus lupulus) and their interaction with haemin.

OBJECTIVES: There is an urgent need to discover new antimalarials, due to the spread of chloroquine resistance and the limited number of available drugs. Chalcones are one of the classes of natural products that are known to possess antiplasmodial properties. Therefore, the in vitro antiplasmodial activity of the main hop chalcone xanthohumol and seven derivatives was evaluated. In addition, the influence of the compounds on glutathione (GSH)-dependent haemin degradation was analysed to determine its contribution to the antimalarial effect of chalcones. METHODS: In vitro antiplasmodial activity was evaluated against the chloroquine-sensitive strain poW and the multiresistant clone Dd2 using a [(3)H]hypoxanthine-incorporation assay. Inhibition of GSH-dependent haemin degradation was analysed by a multiwell plate assay at 11 microM. RESULTS: Of the eight compounds tested, four possessed activity with IC(50) values<25 microM against at least one of the two strains of Plasmodium falciparum. The main hop chalcone, xanthohumol, was most active with IC(50) values of 8.2+/-0.3 (poW) and 24.0 +/- 0.8 microM (Dd2). Three of these compounds were additionally active in the haemin-degradation assay. CONCLUSIONS: The results demonstrate for the first time the ability of chalcone derivatives to interfere with the haemin-degradation process of P. falciparum. This effect might contribute to their antiplasmodial activity. Nevertheless, as one compound showed inhibition of P. falciparum without being able to interact with GSH-dependent haemin degradation, other modes of action must add to the observed antiparasitic activity of hop chalcones.

Animals↗

PubMed1998

Transgene-promoted epigenetic switches of chalcone synthase activity in petunia plants.

Epigenetic variation affecting pigment pattern formation in petunia flowers due to the insertion of transgenes encoding chalcone synthase is described. The loss of pigment formation in petals or parts of petals is due to the post-transcriptional degradation of chalcone synthase RNA, from both the endogenous petunia chalcone synthase genes and from the chalcone synthase transgenes. The RNA cleavage pathway and its control are described. Different epigenetic states of RNA breakdown are correlated with specific cytosine methylation changes in the coding sequences of the genes. The probability, extent and developmental location of chalcone synthase RNA breakdown are related to the number and organization of transgenes in the genome but epigenetic switches that affect RNA turnover probably occur in meristems and between sexual generations. Hypotheses to explain how the transgenes influence the levels of chalcone synthase RNA breakdown and how different epigenetic states are created are discussed.

Acyltransferases↗

PubMed2006

Fragmentation study of protonated chalcones by atmospheric pressure chemical ionization and tandem mass spectrometry.

Fragmentation mechanisms of protonated chalcone and its derivatives with different functional groups were investigated by atmospheric pressure chemical ionization with tandem mass spectrometry (MS/MS). The major fragmentation pathways were loss of the phenyl group from the A or B ring, combined with loss of CO. Losses of H(2)O and CO from the precursor ions of [M+H](+) are proposed to occur via rearrangements. Elimination of water from protonated chalcones was observed in all the title compounds to yield a stable ion but it was difficult to obtain skeletal fragmentation of a precursor ion. Loss of CO was found in the MS/MS spectra of all the compounds except the nitro-substituted chalcones. When the [M+H--CO](+) ion was fragmented in the MS/MS experiments, there were distinctive losses of 15 and 28 Da, as the methyl radical and ethylene, respectively. The ion at m/z 130, found only in the nitro-substituted chalcones, was assigned as C(9)H(6)O by Fourier transform ion cyclotron resonance (FTICR)-MS/MS; m/z 130 is a common fragment ion in the electron ionization (EI) spectra of chalcones. In order to more easily distinguish the constitutional isomers of these chalcones, breakdown curves were produced and these provided strong support in this study.

Journal Article↗

PubMed1986

The role of chalcone synthase in the regulation of flavonoid biosynthesis in developing oat primary leaves.

The role of chalcone synthase in the regulation of flavonoid biosynthesis during organogenesis of oat primary leaves has been investigated at the level of enzyme activity and mRNA translation in vitro. Chalcone synthase was purified about 500-fold. The apparent Km values were 1.5 and 6.3 microM for 4-coumaroyl-CoA and malonyl-CoA, respectively. The end products of oat flavonoid biosynthesis, three C-glucosylflavones, did not inhibit the reaction at concentrations as measured up to 60 microM each. Apigenin (4',5,7-trihydroxyflavone), a stable structural analog of the reaction product, 2',4,4',6'-tetrahydroxychalcone, was found to be a strong competitive inhibitor of 4-coumaroyl-CoA binding and a strong noncompetitive inhibitor of malonyl-CoA binding. Although apigenin is not supposed to be an intermediate of C-glucosylflavone biosynthesis, this compound might be a valuable tool for future kinetic studies. To date, there is no indication of chalcone synthase regulation by feedback or similar mechanisms which modulate enzyme activity. Mathematical correlation of chalcone synthase activity and flavonoid accumulation during leaf development, however, indicates that chalcone synthase is the rate-limiting enzyme of the pathway. By in vitro translation studies using preparations of total RNA from different leaf stages, we could demonstrate for the first time that the translational activity of chalcone synthase mRNA undergoes marked daily changes. The high values found at the end of the dark phase suggest that light does not exert direct influence on flavonoid biosynthesis but probably functions by controlling the basic diurnal rhythm.

Acyltransferases↗