Yellow Strain Research Articles

Mapping of Quantitative Trait Loci Conferring Resistance to Barley Yellow Mosaic Virus in a Chinese Barley Landrace Mokusekko 3.

A Chinese six-rowed barley landrace, Mokusekko 3, exhibits a wide resistance spectrum to all the barley yellow mosaic virus strains in Japan (BaYMV-I, -II, -III) and in Europe (BaYMV-1, -2) as well as to barley mild mosaic virus (BaMMV). To identify the genetic basis for the resistance to BaYMV, a cross between a Japanese malting barley cultivar Ko A (susceptible) and Mokusekko 3 was made to generate F2 and F3 populations. The reaction of the F2-derived F3 lines to BaYMV was investigated in a field infected with BaYMV (-I or both -I and -II) during two growing seasons, 1996 and 1997. BaYMV disease severity of the F2 individuals was quantitatively expressed as the percentage of the susceptible seedlings within the F3 line. For the linkage analysis along the whole chromosome, a map of the barley genome consisting of 100 markers was used. The map covers 1291cM with an average density of 14cM. The interval mapping method was used to identify the quantitative trait loci (QTLs) for resistance to BaYMV. A new QTL for resistance to the BaYMV was located in the terminal region of chromosome 7HS, explaining 20-25% of the phenotypic variance, in addition to those in the terminal region of chromosome 3HL and centromeric region of chromosome 4H. The three QTLs accounted for 55-57% of the total phenotypic variance. The location of the QTLs on chromosomes 4H and 3HL corresponded well to that of rym1 and rym5 which were previously mapped for resistance to BaYMV in Mokusekko 3 using morphological and isozyme markers. Based on these results, the effect of pyramiding of these resistance factors into modern barley cultivars by marker-assisted selection is was examined.

Production of Barley yellow dwarf virus antisera by DNA immunization

Antibodies were produced against the 22-kDa coat protein (CP) of Barley yellow dwarf virus strain PAV (BYDV-PAV) by DNA immunization. A cDNA sequence encoding the 22-kDa CP was cloned into a mammalian expression vector (pcDNA22K), entrapped in liposomes, and injected intramuscularly into BALB/c mice. To target the antigen to sites of immune induction and, thereby, enhance the immune response, the 22-kDa sequence was also fused with the sequence encoding the mouse cytotoxic T-lymphocyte antigen 4 to generate pCTLA422K. Three weeks post immunization, BYDV-PAV-specific immune response was detected in serum. Sera from mice injected with pCTLA422K DNA had significantly higher antibody titers than those from mice injected with pcDNA22K. Increases in antibody titers were observed over time with each subsequent DNA injection. Further, there were large increases in antibody titers when DNA-immunized mice were boosted with purified BYDV-PAV virions. These antibody responses were higher than that obtained by a single injection of purified BYDV-PAV. The results demonstrate that antibodies against BYDV-PAV can be generated using DNA immunization. With this approach, it may be possible to produce antisera against luteoviruses that occur in low concentrations in host plant tissue and are very difficult to purify.

A Variant of Cucumber mosaic virus Is Restricted to Local Lesions in Inoculated Tobacco Leaves with a Hypersensitive Response

A variant of Cucumber mosaic virus, CMV(Y/GM2), was isolated from a tobacco plant with mild green mosaic symptoms that was regenerated in vitro from a yellow strain of CMV [CMV(Y)]-infected tobacco leaves by tissue culture. CMV(Y/GM2) has two amino acid substitutions at 36 and 111 positions in the coat protein encoded on RNA3. CMV, assembled by mixing in vitro transcribed CMV(Y) RNA1 and RNA2 plus infectious RNA3 transcribed in vitro from cDNA to RNA3 of CMV(Y/GM2), was prepared and designated as CMV(Y/GM2)tr. When tobacco (Nicotiana tabacum cv. Xanthi nc) plants were inoculated with CMV(Y/GM2)tr, large necrotic local lesions in which the virus was localized, developed on the inoculated leaves. This host response unique to CMV(Y/GM2)tr was similar to the hypersensitive response (HR), which is a common resistance response to avirulent pathogens and was observed in five cultivars of Nicotiana tabacum and eight Nicotiana species. The revertant virus, however, accumulated to quite different levels in the various hosts. CMV(Y/GM2)tr induced pathogenesis-related 1 (PR-1) protein accumulation and systemic acquired resistance (SAR) which were generally observed in the HR. However, when tobaccos were inoculated with CMV(S36P)tr and CMV(V111I)tr, which have an amino acid substitution at either the 36 or 111 position in the coat protein of CMV(Y), respectively, CMV(S36P)tr was restricted to the primary infection site without necrotic local lesion formation and PR-1 protein and SAR induction. CMV(V111I)tr, however, systemically spread and induced mild green mosaic symptoms, while the host had the HR to CMV(Y/GM2)tr. The localization of CMV(Y/GM2)tr at the primary infection site may not only be caused by the HR, but also by the restriction of virus systemic movement resulting from the amino acid substitution at position 36 in the coat protein of CMV(Y).

Pyrolytic GC-MS analysis of melanin from black, gray and yellow strains of Drosophila melanogaster

Properties of melanins depend strongly on their chemical constitution. Melanins from differently colored strains of Drosophila melanogaster demonstrate various proprieties, and biological activity in the presence of toxic ions or radiation. In the presented work, we analyzed chemical constitution of the melanins derived from black, gray and yellow D. melanogaster strains. Analysis of the products forming during thermal degradation of the biopolymers by pyrolitic gas chromatography followed by mass spectrometry allowed us to determine chemical composition of these biopolymers and classified melanins derived from black and gray strains as eumelanins and derived from yellow strains as pheomelanins. These findings allow us to determine chemical and biological properties of the melanins in vivo, and can explain susceptibility of differently colored strains of D. melanogaster to metal ions.

The French neurotropic vaccine strain of yellow fever virus accumulates mutations slowly during passage in cell culture

This study of the yellow fever French neurotropic vaccine strain from the Institut Pasteur (FNV-IP) demonstrates that this viral genome is not as stable as that of the 17D-204 vaccine virus. FNV-IP was plaque-purified three times and then passaged eight times in Vero cells. Viral populations from the second and eighth passage post purification were sequenced and compared to the published sequences of FNV-IP. The passage-2 viral population had 31 nucleotide and nine amino acid changes compared to the parental virus while the passage-8 virus had six additional nucleotide changes encoding a single amino acid substitution. The plaque-purified virus also had two sequence deletions in the 3′-noncoding region. The plaque purification resulted in selection of a passage-2 virus that had a mouse LD 50 of 20 pfu/ml, 67-fold greater than parental FNV-IP which had an LD 50 of 0.3 pfu/ml. Subsequent passage in Vero cells resulted in a passage-8 virus which had increased neurovirulence with an LD 50 of 3.2 pfu/ml. The only amino acid difference between the passage-2 and passage-8 viruses was at amino acid 638 of NS5 which lies within domain V of the RNA-dependent-RNA polymerase. Overall, these data indicate that FNV-IP virus has an inherently less stable genome than 17D vaccine virus and a variable viral population.

Benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester induces systemic resistance in tomato ( Lycopersicon esculentum. Mill cv. Vollendung) to Cucumber mosaic virus

The potential of benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH) to trigger systemic acquired resistance (SAR) in tomato (Lycopersicon esculentum. Mill cv. Vollendung) plants against a yellow strain of Cucumber mosaic virus (CMV-Y) was investigated. Application of BTH, as a drench, 7 days before inoculation with CMV-Y, protected plants against the necrosis caused by CMV-Y. The resistance was evident as a decreased disease incidence and severity in BTH-treated plants. Twenty-one days after challenge inoculation with CMV-Y, the disease incidence in plants with SAR did not exceed 12.5% whereas, 91.7% of control plants were severely infected. The development of primary disease symptoms in BTH-treated plants was delayed for 7 days. The disease spread rapidly in control plants and by the end of the experiment almost all control plants showed severe mosaic and leaf necrosis. Results of enzyme-linked immunosorbent assay (ELISA) indicated that BTH treatment affected virus replication in protected leaf tissues. Analysis of the newly developed leaves of BTH-treated plants for virus antigen revealed that symptomless plants failed to support the replication of CMV-Y and the concentration of the virus in these plants was similar to that in uninoculated control plants.

Association of ‘Candidatus Phytoplasma australiense’ with green petal and lethal yellows diseases in strawberry

The identity of phytoplasmas detected in strawberry plants with green petal (SGP) and lethal yellows (SLY) diseases was determined by RFLP analysis of the 16S rRNA gene and adjacent spacer region (SR). RFLP and sequence comparisons indicated that the phytoplasmas associated with SGP and SLY were indistinguishable and were most closely related to ‘Candidatus Phytoplasma australiense’, the phytoplasma associated with Australian grapevine yellows, papaya dieback and Phormium yellow leaf diseases. This taxon lies within the aster yellows strain cluster. Primers based on the phytoplasma tuf gene, which amplify only members of the AY strain cluster, amplified a DNA product from the SGP and SLY phytoplasmas. Primers deduced from the 16S rRNA/SR of P. australiense that amplify only members of this taxon amplified rDNA sequences from the SGP and SLY phytoplasmas. Primers that selectively amplify members of the faba bean phyllody (FBP) phytoplasma group, the most commonly occurring phytoplasma group in Australia, did not amplify rDNA from the SGP and SLY phytoplasmas.

Interaction of yellow fever virus French neurotropic vaccine strain with monkey brain: characterization of monkey brain membrane receptor escape variants.

Binding of yellow fever virus wild-type strains Asibi and French viscerotropic virus and vaccine strains 17D and FNV to monkey brain and monkey liver cell membrane receptor preparations (MRPs) was investigated. Only FNV bound to monkey brain MRPs, while French viscerotropic virus, Asibi, and FNV all bound to monkey liver MRPs. Four monkey brain and two mouse brain MRP escape (MRP(R)) variants of FNV were selected at pH 7.6 and 6.0. Three monkey brain MRP(R) variants selected at pH 7.6 each had only one amino acid substitution in the envelope (E) protein in domain II (E-237, E-260, or E274) and were significantly attenuated in mice following intracerebral inoculation. Two of the variants were tested in monkeys and retained parental neurotropism following intracerebral inoculation at the dose tested. We speculate that this region of domain II is involved in binding of FNV E protein to monkey brain and is, in part, responsible for the enhanced neurotropism of FNV for monkeys. A monkey brain MRP(R) variant selected at pH 6.0 and two mouse brain MRP(R) variants selected at pH 7.6 were less attenuated in mice, and each had an amino acid substitution in the transmembrane region of the E protein (E-457 or E-458).

Characterization of symptom determinants in two mutants of cucumber mosaic virus Y strain, causing distinct mild green mosaic symptoms in tobacco

Two mutants of Cucumber mosaic virus, CMV(Y/GM1) and CMV(Y/GM2), which induced mild green mosaic symptoms in tobacco, were isolated from plants regenerated from tobacco leaves with yellow mosaic symptoms originally infected with the yellow strain of CMV [CMV(Y)]. Although the appearance of mild green mosaic symptoms in tobacco infected with CMV(Y/GM2) was unstable, CMV(Y/GM3) derived from CMV(Y/GM2) reproducibly induced mild green mosaic symptoms in tobacco similar to CMV(Y/GM1). A comparison of the deduced amino acid sequences of the coat proteins of CMV(Y), CMV(Y/GM1) and CMV(Y/GM3), showed single amino acid substitutions from Thr to Ile at position 124 in the CMV(Y/GM1) coat protein and from Val to Ile at position 111 in the CMV(Y/GM3) coat protein. When the amino acid at the 124 or 111 position in the CMV(Y) coat protein was changed to Ile at the cDNA level, CMV RNA3 transcribed in vitro from each cDNA induced mild green mosaic symptoms in tobacco after inoculation with in vitro transcribed CMV(Y) RNA1 and RNA2. The results indicated that amino acids at positions 111 and 124 in the coat protein were responsible for the phenotypic changes caused by the two CMV isolates.

First Report of Clover Yellow Edge Phytoplasma in Corylus (Hazelnut).

During investigations into the cause of a stunt syndrome affecting cultivated European hazelnut trees (Corylus avellana L.) in Oregon, the clover yellow edge (CYE) phytoplasma was detected for the first time in this crop. The cause of hazelnut stunt syndrome (HSS) is unknown, but the disease has been transmitted by grafting and apparently has moved within orchards through root grafts (1). Severely affected trees persist for many years, but their nut production is greatly reduced. Previous attempts to detect viruses, bacteria, and other pathogens have been unsuccessful. HSS has been observed only in Oregon and already had been present for more than 10 years when it was first reported in 1970 (1). In June, 1999, leaf samples were collected from two affected and two apparently healthy (symptomless) hazelnut trees in a field plot at Oregon State University, Corvallis, and from a healthy greenhouse-grown tree. Leaf samples were sent to the USDA Beltsville, MD, laboratory, where they were assessed for phytoplasma infection, using nested polymerase chain reactions (PCRs). PCRs were primed by phytoplasma universal primer pairs P1/P7 and F2n/R2 (3) for amplification of phytoplasma 16S ribosomal (r) DNA (16S rRNA gene) sequences according to the procedures of Gunderson and Lee (2). Phytoplasma-characteristic 1.2-kbp DNA sequences were amplified from all field-tree samples. No DNA sequences were amplified from samples of the greenhouse-grown tree. Restriction fragment length polymorphism patterns of rDNA digested with AluI, KpnI, HhaI, HaeIII, HpaII, MseI, RsaI, and Sau3A1 endonucleases indicated that all diseased hazelnut trees as well as symptomless field trees were infected by a phytoplasma classified in group 16SrIII (peach X-disease group), subgroup B (III-B, type strain CYE phytoplasma). No phytoplasmas were detected in samples from the greenhouse-grown tree. Nucleotide sequences were determined for 16Sr DNA fragments amplified from the hazelnut CYE phytoplasma in nested PCRs primed with F2n/R2. The sequences were deposited in GenBank under Accession no. AF189288. Sequence similarity between 16Sr DNAs of the hazelnut CYE strain (CYE-Or) and the Canadian clover yellow edge strain (CYE-C, GenBank Accession no. AF175304) phytoplasma was 99.9%. Decline and yellows disorders of hazelnut in Germany and Italy have been associated with infections by apple proliferation, pear decline, and European stone fruit yellows phytoplasmas (4). These phytoplasmas are classified in 16Sr group X, the apple proliferation group of phytoplasmas. This is the first report of the CYE phytoplasma infecting Corylus.

Antibody-mediated improved resistance to ClYVV and PVY infections in transgenic tobacco plants expressing a single-chain variable region antibody

Transgenic Nicotiana tabacum plants expressing a single-chain variable region antibody fragment derived from a broad-spectrum monoclonal antibody 3-17 showed suppression of virus infection following challenge by two distinct potyviruses: potato virus Y strain D, and clover yellow vein virus strain 300. Monoclonal antibody 3-17, which was raised against the potyvirus Johnsongrass mosaic virus, was shown to react strongly with 14 potyvirus species. Two different single-chain antibody constructs were used to produce chimeric genes encoding recombinant proteins designed to be targeted either to the apoplasm or to the cytoplasm. Transgenic plant lines showed reduced numbers of local lesions and systemic symptoms when challenged with potato virus Y, strain D and reduced local lesions following challenge with clover yellow vein virus, strain 300. The level of suppression conferred by the transgene when plants were challenged under laboratory conditions with high concentrations of virus, together with the ability of the transgene to partially protect plants against distinct viruses suggest that one single-chain gene construct might be used to protect plants from distinct potyviruses.

Complete nucleotide sequence and phylogeny of an American strain of yellow fever virus, TRINID79A.

Yellow fever was presumably imported to the Americas from West-Africa from the 16th to the 19th century. American and African genotypes of the virus are distinguishable, indicating separate evolution in different vector/host cycles. The complete nucleotide sequence of the yellow fever virus strain TRINID79A, isolated in Trinidad in 1979, has been established. It exhibits extensive homology with those of current West-African strains and attenuated strain FNV. However, a unique deletion of the 3' non-coding region (NCR) of the viral RNA has been identified. It indicates that RYF1 and RYF2 repeated sequences of the 3' NCR are not necessary to the replication of the virus.

Water composition and loss by body color and form mutants of the German cockroach (Dictyoptera: Blattellidae)

Body water composition and rates of water loss were determined for adult males of five body color or form mutants of the German cockroach, Blattella germanica (L.). Body water content ranged from 68.4% for a yellow body strain to 74.7% for the balloon wing strain. Dark body strains (black and black×orange) contained less water than lighter color strains (orange and yellow). There were no differences in whole-body lipid content among the strains. Cuticular permeability at 30°C ranged from 18.44 to 24.8 μg cm -2 h -1 mmHg -1 for black body and balloon wing strains, respectively; dark body strains had lower cuticular permeabilities than light body strains. Brief, whole-body extraction with hexane increased cuticular permeability from 5.6-fold for the balloon strain to 8.3-fold for the orange body strain. Cuticular permeabilities of hexane-extracted dark body strains again had lower cuticular permeabilities than those of light body strains, indicating that differences in permeability were due to the cuticle itself and not differences in the amount or composition of epicuticular lipids. Measurements of cuticle water content indicated that light body strains contained significantly more water than dark body strains. Rate of percent original mass and percentage of total body water lost increased linearly with time. Implications of cuticular water content to cuticular permeability are discussed.

Production of poly(β-hydroxybutyric acid) and exopolysaccharide by Azotobacter beijerinckii WDN-01

The physico-chemical factors influencing the production of poly(β-hydroxybutyric acid) [PHB] and exopolysaccharide (EPS) by a yellow pigmented Azotobacter beijerinckii strain WDN-01 were investigated. Under N-free condition with excess carbon, PHB accumulation attained its maximum at the late exponential phase followed by a sharp decline while EPS production was more or less parallel with growth. Polymer synthesis, however, was carbon-source-specific, the highest yield of PHB (2.73 g/l) and EPS (1.5 g/l) was obtained with 3% (w/v) glucose and mannitol respectively. Organic N-sources enhanced PHB production significantly, but inorganic nitrogenous compounds were inhibitory to both PHB and EPS synthesis. At optimum K2HPO4 concentration, the polymer yield was attributed to biomass yield. Oxygen-limiting conditions, irrespective of carbon sources favoured production of PHB and EPS.

Development of viremia and humoral and cellular parameters of immune activation after vaccination with yellow fever virus strain 17D: a model of human flavivirus infection.

To monitor early and late events of immune system activation after primary and secondary flavivirus infection, 17 healthy persons were vaccinated with the standard 17D vaccine virus strain of yellow fever (YF). Twelve of these persons had not received YF vaccine previously and 5 had been vaccinated once at least 10 years before. Viremia and various parameters of humoral and cellular immune activation were followed daily for 7 days and weekly thereafter. Viremia was detected by reverse transcriptase-polymerase chain reaction in all 12 first-time vaccinees beginning from the second to the sixth day after vaccination; most tested positive between the fourth and sixth day. Infectious 17D virus was detected using a plaque forming assay in the serum of 7 of the 12 first-time vaccinees. As first parameters of immune activation, neopterin and beta2-microglobulin markedly increased between day 2 and day 6 postvaccination. In parallel to the viremia, circulating CD8+ T-cells significantly increased, with peak levels at day 5 after primary vaccination, indicating an activation of the cellular immune system. Neither viremia nor significant changes of these activation markers were observed in the five revaccinated persons. Neutralizing antibodies directed against the 17D vaccine strain developed in all persons within 2 weeks after vaccination. No correlation was found between the extent of viremia and the titer of neutralizing antibodies. Revaccination was followed by a minor and transient increase of neutralizing antibodies. High titers of neutralizing antibodies persisted for at least 10 years after primary vaccination.

In Situ Localization of Barley Yellow Dwarf Virus-PAV 17-kDa Protein and Nucleic Acids in Oats

ABSTRACT Barley yellow dwarf virus strain PAV (BYDV-PAV) RNA and the 17-kDa protein were localized in BYDV-PAV-infected oat cells using in situ hybridization and in situ immunolocalization assays, respectively. The in situ hybridization assay showed labeling of filamentous material in the nucleus, cytoplasm, and virus-induced vesicles with both sense and antisense nucleic acid probes, suggesting that the filamentous material found in BYDV-PAV-infected cells contains viral RNA. BYDV-PAV negative-strand RNA was detected before virus particles were observed, which indicates that RNA replication is initiated before synthesis of viral coat protein in the cytoplasm. The 17-kDa protein was associated with filamentous material in the cytoplasm, nucleus, and virus-induced vesicles. The labeling densities observed using antibodies against the 17-kDa protein were similar in the nucleus and cytoplasm. No labeling of the 17-kDa protein was observed in plasmodesmata, but filaments in the nuclear pores occasionally were labeled. Since BYDV-PAV RNA and 17-kDa protein colocalized within infected cells, it is possible that single-stranded viral RNA is always associated with the 17-kDa protein in vivo. The 17-kDa protein may be required for viral nucleic acid filaments to traverse the nuclear membrane or other membrane systems.

Differential detection and genetic relatedness of phytoplasmas in papaya

The genetic relatedness of phytoplasmas associated with dieback (PDB), yellow crinkle (PYC) and mosaic (PM) diseases in papaya was studied by restriction fragment length polymorphism (RFLP) analysis of the 16S rRNA gene and 16S rRNA/23S rRNA spacer region (SR). RFLP and SR sequence comparisons indicated that PYC and PM phytoplasmas were identical and most closely related to members of the faba bean phyllody strain cluster. By comparison the PDB phytoplasma was most closely related to Phormium yellow leaf (PYL) phytoplasma from New Zealand and the Australian grapevine yellows (AGY) phytoplasma from Australia. These three phytoplasmas cluster with the stolbur and German grapevine yellows (VK) phytoplasmas within the aster yellows strain cluster. Primers based on the phytoplasma tuf gene, which amplify gene products from members of the AY strain cluster, also amplified a DNA product from the PDB phytoplasma but not from either the PYC or PM phytoplasmas. Primers deduced from the 16S rRNA/SR selectively amplified rDNA sequences from the PDB and AGY phytoplasmas but not from other members of the stolbur strain cluster. Similarly, primers designed from 16S rRNA/SR amplified rDNA from the PYC and PM phytoplasmas but not from the PDB phytoplasma. These primers may provide for more specific detection of these pathogens in epidemiological studies.

Enzymatic hydroxylation of 6′-deoxychalcones with protein preparations from petals of Dahlia variabilis

Yellow colouration of Dahlia variabilis flowers is mainly based on isoliquiritigenin and butein 4′-malonylglucosides. Microsomal preparations from petals of the yellow strain ‘Johann Nestroy’ catalyse the enzymatic 3-hydroxylation of isoliquiritigenin to butein in the presence of NADPH. The reaction showed a pH optimum of 7.5, and was inhibited by p-hydroxymercuribenzoate and a number of cytochrome P450 specific inhibitors. These and further properties suggest that the 3-hydroxylation of isoliquiritigenin is mediated by a cytochrome P450-dependent monooxygenase. The apparent K m value for isoliquiritigenin was 50 μM.

Stimulated ethylene production in tobacco ( Nicotiana tabacum L. cv. Ky 57) leaves infected systemically with cucumber mosaic virus yellow strain

Ethylene production was stimulated in the leaves of tobacco ( Nicotiana tabacum L. cv. Ky 57) infected systemically with cucumber mosaic virus yellow strain (CMV-Y). This observation was made with the 9th leaf of tobacco plants which had been inoculated with CMV-Y on the 6th leaf at the middle stage of growth. A transient peak of ethylene production per fresh-weight base appeared 2 weeks after inoculation when the mosaic symptoms of green, yellow and white sectors covered about 40% of the leaf area. The increase in ethylene production was accompanied by an increase in 1-aminocyclopropane-1-carboxylate (ACC) content and activities of ACC synthase and ACC oxidase in systemically-infected leaves. Among three sectors with different colors in CMV-Y-infected mosaic leaves, ACC content was highest in the green sector, implying ethylene production took place most actively there.

Enzymatic hydroxylation of 6′-deoxychalcones with protein preparations from petals of dahlia variabilis

Yellow colouration of Dahlia variabilis flowers is mainly based on isoliquiritigenin and butein 4′-malonylglucosides. Microsomal preparations from petals of the yellow strain ‘Johann Nestroy’ catalyse the enzymatic 3-hydroxylation of isoliquiritigenin to butein in the presence of NADPH. The reaction showed a pH optimum of 7.5, and was inhibited by p-hydroxymercuribenzoate and a number of cytochrome P450 specific inhibitors. These and further properties suggest that the 3-hydroxylation of isoliquiritigenin is mediated by a cytochrome P450-dependent monooxygenase. The apparent Km value for isoliquiritigenin was 50 μM.