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PubMed1994

Cellular protein receptors of maculosin, a host specific phytotoxin of spotted knapweed (Centaurea maculosa L.).

Maculosin (the diketopiperazine, cyclo (L-Pro-L-Tyr)) is a host specific phytotoxin produced by Alternaria alternata on spotted knapweed (Centaurea maculosa L.). Receptors for this phytotoxin have been isolated from spotted knapweed. Knapweed leaves possess most of the maculosin-binding activity in the cytosolic fraction. However, activity was also observed in the whole membrane fraction of the leaf. The binding component of the cytosolic fraction was identified as a protein(s) because of its heat-lability and sensitivity to proteases. A 16-fold purification of a toxin-binding protein was carried out by ammonium sulfate fractionation, and Sephadex G-200, and maculosin-affinity column chromatography. The affinity column was prepared with epoxy activated Sepharose 6B to which the phenolic group of maculosin was attached. The receptor was estimated to contain more than one binding protein by native and SDS-PAGE. At least one of the maculosin-binding proteins was identified as ribulose-1,5-biphosphate carboxylase (RuBPcase).

Binding Sites↗
PubMed1983

Some pharmacological, toxicological and phytochemical investigations on Centaurea phyllocephala.

Centaurea phyllocephala Boiss. has been used in folkloric medicine as an antidiabetic agent. Present investigations on various extracts of C. phyllocephala revealed that basal plasma glucose concentration and plasma glucose response to glucose load were either elevated or unchanged by the i.v. administration of these extracts in anaesthetized rats or by i.p. or oral administration of the extracts in conscious rats. The predominant effect of C. phyllocephala is the toxicity in rats and mice and this indicates the presence of some toxic or active compounds which merit phytochemical isolation. Further, C. phyllocephala extracts also caused either an initial brief hypotension followed by a delayed hypertension or produced no changes when injected i.v. in the rats. The hypotensive effect was inhibited by atropine whereas the hypertensive effect was prevented by phentolamine or guanethidine but not by hexamethonium. The alcoholic extract also induced an initial brief negative inotropic effect, followed by delayed prolonged positive inotropic and negative chronotropic effects on the spontaneous inotropic and negative chronotropic effects on the spontaneous contractions of the guinea pig right atrium. The initial depressing effect and the delayed positive inotropic effect were inhibited by pretreatment with atropine. The extract of C. phyllocephala also produced a contractile activity on guinea pig ileum strips and this could be prevented by atropine. No significant diuretic effect was produced by the extract. Phytochemical screening revealed that C. phyllocephala contains tertiary and quaternary alkaloids, sesquiterpene lactones, methylated flavones and their glycosides, as well as leuco- and proanthocyanidines. Further studies on sesquiterpene lactones and methylated flavones resulted in the isolation of lactones with alpha-methylene gamma-lactone and methylene side chain on the cyclopentyl ring as well as of four methylated flavones (hispidulin, nepetin, cirsiliol, jaceosidin) structurally closely related to the cytotoxic flavonoids of other Compositae plants.

Animals↗
PubMed1993

Two new antiinflammatory elemanolides from Centaurea chilensis.

Two previously undescribed elemanolide esters, the 2-methylpropanoate and 2-methyl-2-propenoate of 11,13-dehydromelitensin, were isolated in the course of a bioassay-guided fractionation from the aerial parts of Centaurea chilensis Hook. et Arn., used traditionally to treat 'gout and rheumatism'. The mixture of both substances exhibits anti-inflammatory activity in the carrageenan-induced paw edema assay.

Animals↗
PubMed2001

Two flavonoids and other compounds from the aerial parts of Centaurea bracteata from Italy.

The flowering aerial parts of Centaurea bracteata Scop. (Asteraceae) have been studied for the first time. Nineteen compounds were isolated and identified, namely a sterol glucoside, two phenolic acids, three quinic acid derivatives, and 13 flavonoids, two of which, are new natural products. Structural elucidation was performed mainly by mean of FABMS, 1D and 2D NMR spectroscopy.

Asteraceae↗
PubMed2001

Indole alkaloids from the seeds of Centaurea cyanus (Asteraceae).

Preparative RP-HPLC analysis of a methanol extract of the seeds of Centaurea cyanus afforded four indole alkaloids: moschamine, cis-moschamine, centcyamine and cis-centcyamine, the latter two being new natural products. Structures of these compounds were elucidated by comprehensive spectroscopic analyses. General toxicity of the isolates was determined by Brine Shrimp Lethality bioassay.

Alkaloids↗
PubMed2001

A flavonoid sulphate and other compounds from the roots of Centaurea bracteata.

The roots of Centaurea bracteata Scop. (Asteraceae) have been studied for the first time. Twenty-three compounds were isolated and identified, namely a sterol glucoside, two quinic acid derivatives, one sugar, and 19 flavonoids (five sulphates), one of which, centaradixin, resulted in a new natural product. Structural elucidation was performed mainly by means of FABMS, 1D and 2D NMR spectroscopy. NMR data of some sulphate flavonoids are reported for the first time.

Asteraceae↗
PubMed1998

Sesquiterpene lactones of Centaurea scoparia.

From the ethanolic extract of the aerial parts of Centaurea scoparia four new sesquiterpene lactones, belonging to the guaiane class, were isolated and identified, together with a known germacranolide. The structures were elucidated by spectroscopic methods including one- and two-dimensional NMR studies. The relative configuration was deduced from the 2D NOESY spectra. CD spectroscopy of the chlorinated compounds was used for determination of their absolute configuration.

Journal Article↗
PubMed1999

Guaianolides from Centaurea nicolai: antifungal activity.

A new guaianolide, 3-deacetyl-9-O-acetylsalograviolide A, along with four known closely related lactones, salograviolide A, 9-O-acetylsalograviolide A, kandavanolide and salograviolide B were detected in the aerial parts of the flowering plant Centaurea nicolai. Antifungal tests performed on salograviolide A and its 9-O-acetyl and 3-O-deacetyl-9-O-acetyl derivatives revealed inhibitory activity against Aspergillus niger, A. ochraceus, Penicillium ochrochloron, Cladosporium cladosporoides, Fusarium tricinctum and Phomopsis helianthi. Neither of them was active against Trichoderma viride.

Antifungal Agents↗
PubMed1997

Inhibition of tomato bushy stunt virus infection using a quercetagetin flavonoid isolated from Centaurea rupestris L.

Flower and leaf extracts of Centaurea rupestris L. and also the flavonoid quercetagetin 3'-methylether isolated from these extracts revealed a strong antiviral activity when inoculated simultaneously with tomato bushy stunt virus in two Nicotiana species. Almost complete reduction of local lesion number resulted from these inoculations in N. glutinosa. A similar effect was observed in inoculated leaves of N. megalosiphon causing the absence of systemic infection in 40% of treated plants. The antiphytoviral activity was not a consequence of induced resistance, inhibition of virus multiplication, suppression of symptom development or direct virus inactivation. Results presented in this paper suggest that the flavonoid may interfere with the initiation of virus infection.

Antiviral Agents↗
PubMed2001

Sesquiterpene lactones from Centaurea tweediei.

Aerial parts of Centaurea tweediei from Argentina afforded as the main constituent the sesquiterpene lactone onopordopicrin and minor amounts of a new heliangolide, a new guaianolide, a new eudesmanolide, a new eudesmane acid and the lignans arctigenin and matairesinol.

Journal Article↗
PubMed1999

Anti-inflammatory and immunological effects of Centaurea cyanus flower-heads.

Centaurea cyanus flower-heads are used in European phytotherapy for the treatment of minor ocular inflammations. Different pharmacological experiments (inhibition of carrageenan, zymosan and croton oil-induced oedemas, inhibition of plasma haemolytic activity, induction of anaphylatoxin activity) showed that polysaccharides extracted from C. cyanus flower-heads had anti-inflammatory properties and interfered with complement. Moreover, these polysaccharides were found to be mainly composed of galacturonic acid, arabinose, glucose, rhamnose and galactose.

Anaphylatoxins↗
PubMedDate not supplied

Guaianolides and eudesmanolides from Centaurea ornata.

Four sesquiterpene lactones and three other compounds have been isolated from the EtOH-H2O-soluble fraction of a CHCl3 extract of Centaurea ornata. A new grosshemin derivative 3 is described, and the stereochemistry of natural 11-epi-dihydroreynosin [2] is revised.

Benzaldehydes↗
PubMed2000

A new flavonoid glycoside from Centaurea horrida.

A new natural compound, horridin (1), was isolated from the aerial parts of Centaurea horrida. Its structure as quercetin 3-O-alpha-L-rhamnopyranosyl-(1-->2)-alpha-L-rhamnopyranoside was determined by spectroscopic methods, including 2D NMR.

Asteraceae↗
PubMed2001

Allozyme segregation and inter-cytotype reproductive barriers in the polyploid complex Centaurea jacea.

In eastern Belgium, diploid and tetraploid knapweeds (Centaurea jacea L. s. l.) show a parapatric distribution with a contact zone. To compare the success of inter- and intra-cytotype crosses, and to investigate the pattern of allozyme segregation, controlled crosses involving plants from this contact zone were performed. Polysomic inheritance at two loci was observed in tetraploids, suggesting an autopolyploid origin. Two crosses allowed the detection of double reduction events in tetraploids at one locus, but no such event was detected among the 217 progenies. Null alleles were detected in tetraploids at two loci. Both cytotypes were highly self-incompatible. Inter-cytotype crosses were much less successful than intra-cytotype crosses in terms of seed set (five-fold reduction) and germination rates (three-fold reduction), suggesting a 'triploid block' effect. Progenies from inter-cytotype crosses most often had the maternal cytotype and resulted from selfing or pollen contamination. However, six triploids were detected. The significance of these results for the understanding of the geographical distribution of the cytotypes and inter-cytotype gene flow is discussed.

Alleles↗
PubMed2001

Comparative allozyme and microsatellite population structure in a narrow endemic plant species, Centaurea corymbosa Pourret (Asteraceae).

Centaurea corymbosa Pourret (Asteraceae) is a narrow endemic species known only from six populations located in a 3-km2 area in the south of France. Earlier field experiments have suggested that pollen and seed dispersal were highly restricted within and among populations. Consistent with the field results, populations were highly differentiated for five allozyme loci and among-population variation fitted an isolation-by-distance model. In the present study, we investigated the genetic structure of C. corymbosa using six microsatellite loci. As with allozymes, microsatellites revealed no within-population structure and a large differentiation among populations. However, allozyme loci were less powerful than microsatellites in detecting the extent of gene flow assessed by assignment tests. The patterns of structuration greatly varied among loci for both types of marker; we suggest that differences in single-locus pattern could mainly be an effect of stochastic variation for allozymes and an effect of variation in mutation rate for microsatellites. In contrast to the multilocus results, the two most polymorphic microsatellite loci did not show any isolation-by-distance pattern. Our results suggest that highly variable loci might not always be the best suited markers to quantify levels of gene flow among populations.

Asteraceae↗
PubMed2000

Purification, cloning and autoproteolytic processing of an aspartic proteinase from Centaurea calcitrapa.

Plant aspartic proteinases (APs) have been isolated from several seed and leaf sources but the only well characterized enzymes from flowers are cardosins and cyprosins from cardoon, Cynara cardunculus L. Here we report a full-length cDNA clone encoding an AP named cenprosin from the flowers of Centaurea calcitrapa L., a thistle related to cardoon. As found for all eukaryotic APs, the deduced primary sequence consists of a signal sequence, a propart and a mature enzyme. In addition, an internal sequence region of 104 residues typical only of plant APs (a plant-specific insert) is present in the primary structure. Northern analysis revealed that the strongest expression is in fresh flowers. The enzyme is also expressed in fairly high amounts in seeds and in leaves, a feature not detected for cardoon APs. The corresponding enzyme was purified in its precursor form from fresh flowers using ammonium-sulfate precipitation followed by ion-exchange and hydrophobic-interaction chromatography. The processing of the precursor into its mature form was studied in vitro. The enzyme underwent autocatalytic processing at pH 3.0 resulting in two chains of 16 and 30 kDa. When dried flowers were used as a starting material for purification, only 16- and 30-kDa chains were obtained, suggesting that autoproteolytic activation of procenprosin in vivo occurs mainly during drying of the flowers. This may indicate a specific degradative role for the enzyme during senescence of the flowers.

Amino Acid Sequence↗