Effects of seven pure flavonoids from mosses on germination and growth of Tortula muralis HEDW (Bryophyta) and Raphanus sativus L (Magnoliophyta)

Developments in the stereoselective synthesis of benzopyran, benzopyrone and flavonoid based natural product analogues using C-glycosides as an intrinsic chiral synthon

Stereoselective synthesis is essential for propelling mainstream academia toward a relentless pursuit of novel and cutting-edge strategies for constructing molecules with unparalleled precision. Naturally derived benzopyrans, benzopyrones, and flavonoids are an essentially prominent group of oxa-heterocycles, highly significant targets in medicinal chemistry owing to their extensive abundance in biologically active natural products and pharmaceuticals. The molecular complexity and stereoselectivity induced by heterocycles embedded with C-glycosides have attracted considerable interest and emerged as a fascinating area of research for synthetic organic chemists. This present article emphasizes the existing growths in the strategies involving the diastereoselective synthesis of C-glycosylated benzopyrans, benzopyrones, and flavonoids using naturally acquired glycones as chiral synthons.

Chemical diversity of Brittonodoxa subpinnata, a Brazilian native species of moss

Plants should be probably thought of as the most formidable chemical laboratory that can be exploited for the production of an incredible number of molecules with remarkable structural and chemical diversity that cannot be matched by any synthetic libraries of small molecules. The bryophytes chemistry has been neglected for too long, but in the last ten years, this scenery is changing, with several studies being made using extracts from bryophytes, aimed at the characterization of interesting metabolites, with their metabolome screened. The main objective of this study was to analyze the metabolome of Brittonodoxa subpinnata, a native Brazilian moss species, which occurs in the two Brazilian hotspots. GC-MS and LC-MS2 were performed. All extracts were analyzed using the molecular networking approach. The four extracts of B. subpinnata (polar, non-polar, soluble, and insoluble) resulted in 928 features detected within the established parameters. 189 (20.4%) compounds were annotated, with sugars, fatty acids, flavonoids, and biflavonoids as the major constituents. Sucrose was the sugar with the highest quantity; palmitic acid the major fatty acid but with great presence of very long-chain fatty acids rarely found in higher plants, glycosylated flavonoids were the major flavonoids, and biflavonoids majorly composed by units of flavones and flavanones, exclusively found in the cell wall. Despite the high percentage, this work leaves a significant gap for future works using other structure elucidation techniques, such as NMR.

Interspecific competition affects spore germination and gametophore development of mosses

Background

Interactions between moss species in their earliest growth stages have received little attention. To what extent interspecific competition or priority effects influence spore germination, protonemal development and gametophore emergence is unknown. We evaluated such effects in pairwise interaction between six common bryophyte species: Atrichum undulatum, Bryum argenteum, Ceratodon purpureus, Funaria hygrometrica, Hypnum cupressiforme, Leptobryum pyriforme.

Methods

Interspecific interactions were assessed in vitro. Spores were sterilized and sown on agar plates in three treatments: 1) as single species cultures (controls), 2) as pairwise species cultures inoculated simultaneously, and 3) with a time lag of 20 days between species. Data on time needed for spore germination, germination rate, the time needed for gametophore differentiation, number of gametophores per germinated spore and average diameter of colonies were collected. We also performed spore germination tests in single-species cultures at the start and end of the study, as well as tests for density-dependency at spore germination and gametophore formation.

Results

We observed strong pairwise interactive effects when sowing spores of different species simultaneously or with a delay of 20 days. The results indicate that spore germination is often inhibited by interspecific competition. The first species has an advantage as compared to the later colonizing species, i.e., an apparent priority effect. Interspecific interactions were also evident during gametophore development and included both inhibition and facilitation.

Conclusion

We found pronounced differences in the relative performance of species in interaction with other species during spore germination and gametophore formation. Allelopathic effects are the most probable explanation for these observations. Our results under sterile lab conditions are likely to reflect processes that occur in the wild, governing biotic filtering and bryophyte community assembly during primary and secondary colonization.

Luteolin: A promising natural agent in management of pain in chronic conditions

Pain due to chronic conditions is a frequent and insufficiently addressed problem. Current drug options for pain management (either in cases of chronic inflammatory conditions or neuropathy) do not adequately treat pain. Moreover, they are associated with important adverse events in long term use. Luteolin is a flavonoid widely present in the plant kingdom and its sources have been assembled in a comprehensive list of this paper. Luteolin has shown in several research studies a range of pharmacological properties; anti-inflammatory, antioxidant, neuroprotective, and analgesic. In this article, we summarize the effects and potential benefits from introducing luteolin as an adjuvant agent in established protocols for pain management. We review the most indicative in vivo and in vitro evidence of how luteolin can target the molecular pathways involved in pathogenesis of chronic inflammatory and neuropathic pain. The data reviewed strongly support luteolin's promising benefits in pain management and raise the need for further clinical trials that can establish its role in clinical practice.

Allelopathic Potential of Mangroves from the Red River Estuary against the Rice Weed Echinochloa crus-galli and Variation in Their Leaf Metabolome

Mangroves are the only forests located at the sea–land interface in tropical and subtropical regions. They are key elements of tropical coastal ecosystems, providing numerous ecosystem services. Among them is the production of specialized metabolites by mangroves and their potential use in agriculture to limit weed growth in cultures. We explored the in vitro allelopathic potential of eight mangrove species’ aqueous leaf extracts (Avicennia marina, Kandelia obovata, Bruguiera gymnorhiza, Sonneratia apetala, Sonneratia caseolaris, Aegiceras corniculatum, Lumnitzera racemosa and Rhizophora stylosa) on the germination and growth of Echinochloa crus-galli, a weed species associated with rice, Oryza sativa. Leaf methanolic extracts of mangrove species were also studied via UHPLC-ESI/qToF to compare their metabolite fingerprints. Our results highlight that A. corniculatum and S. apetala negatively affected E. crus-galli development with a stimulating effect or no effect on O. sativa. Phytochemical investigations of A. corniculatum allowed us to putatively annotate three flavonoids and two saponins. For S. apetala, three flavonoids, a tannin and two unusual sulfated ellagic acid derivatives were found. Some of these compounds are described for the first time in these species. Overall, A. corniculatum and S. apetala leaves are proposed as promising natural alternatives against E. crus-galli and should be further assessed under field conditions.

Advances in plant-derived C-glycosides: Phytochemistry, bioactivities, and biotechnological production

C-glycosides represent a large group of natural products with a C-C bond between the aglycone and the sugar moiety. They exhibit great structural diversity, wide natural distribution, and significant biological activities. By the end of 2021, at least 754 C-glycosides and their derivatives have been isolated and characterized from plants. Thus far, 66 functional C-glycosyltransferases (CGTs) have been discovered from plants, and provide green and efficient approaches to synthesize C-glycosides. Herein, advances in plant-derived C-glycosides are comprehensively summarized from aspects of structural diversity and identification, bioactivities, and biotechnological production. New strategies to discover novel C-glycosides and CGTs, as well as the applications of biotechnological methods to produce C-glycosides in the future are also discussed.

Stress, senescence, and specialized metabolites in bryophytes

Life on land exposes plants to varied abiotic and biotic environmental stresses. These environmental drivers contributed to a large expansion of metabolic capabilities during land plant evolution and species diversification. In this review we summarize knowledge on how the specialized metabolite pathways of bryophytes may contribute to stress tolerance capabilities. Bryophytes are the non-tracheophyte land plant group (comprising the hornworts, liverworts, and mosses) and rapidly diversified following the colonization of land. Mosses and liverworts have as wide a distribution as flowering plants with regard to available environments, able to grow in polar regions through to hot desert landscapes. Yet in contrast to flowering plants, for which the biosynthetic pathways, transcriptional regulation, and compound function of stress tolerance-related metabolite pathways have been extensively characterized, it is only recently that similar data have become available for bryophytes. The bryophyte data are compared with those available for angiosperms, including examining how the differing plant forms of bryophytes and angiosperms may influence specialized metabolite diversity and function. The involvement of stress-induced specialized metabolites in senescence and nutrient response pathways is also discussed.

Biological Activity and Phytochemical Analysis of Dicranum scoparium against the Bacterial Disease for Honey Bee

Bacterial diseases, such as American Foulbrood (AFB) and European Foulbrood (EFB), are known to have catastrophic effects on honey bees (if left to spread, can wipe out entire colonies), leading to severe financial losses in the beekeeping industry. The aim of this study was to evaluate the pharmacological properties of methanol extract and its fractions (ethyl acetate, hexane, water) derived from Dicranum scoparium Hedw., which could be utilized as a potential drug to prevent the bacterial diseases (AFB and EFB) affecting the honey bees. For this purpose, crude methanol extract and ethyl acetate/hexane/water fractions were prepared from the aerial part of D. scoparium, collected from Trabzon province. Bio-guided fractionation of the extract and its fractions led to the first-time isolation of five compounds. The structure of all compounds was elucidated by nuclear magnetic resonance (NMR) spectroscopy, ultraviolet (UV) spectral analysis, Fourier-transform infrared spectroscopy (FT-IR), liquid chromatography quadrupole time-of-flight mass spectroscopy (LC-QToF-MS), and by comparison of their NMR data with that of literature. The analysis of these compounds revealed significant antibacterial and sporicidal activities against bacteria causing larval diseases in honey bees. The antibacterial activity of these compounds ranged from 0.6 to 60 μg/mL against AFB and EFB causing bacteria. Therefore, the natural raw extract and fractions of D. scoparium could be used as potential therapeutic agents against bacterial agents affecting honey bees.

Identification of Barley (Hordeum vulgare L. subsp. vulgare) Root Exudates Allelochemicals, Their Autoallelopathic Activity and Against Bromus diandrus Roth. Germination

Crops with weed suppressive root exudates or the direct use of bioherbicidal allelochemicals is a new approach in integrated weed management systems. In this context, the allelopathic activity and chemical composition of root exudates from six genotypes (modern varieties and landraces) of barley were characterized. The phenolic acids appeared to be particularly implicated in the inhibitory action of barley root exudates against Bromus diandrus. The amount of these compounds was higher in sandy substrate than in sandy-clay-loam substrate. Ten phenolic acids and one phenylpropanoid derivative were present, in addition to saponarin, a newly identified flavonoid in barley root exudates. Seven compounds explaining variability in the inhibitory activity of barley roots (stepwise analysis) and one compound detected only in highly allelopathic genotypes were toxic against receiver plants. Most compounds had a greater inhibitory effect on the growth of great brome than the barley genotypes. The synergistic and/or additive effect of the eight compounds appeared to be the source of the toxicity. Benzoic acid, the mixture of compounds, saponarin and salicylic acid were the most efficient compounds against the great brome and the less aggressive against barley. Overall, the results revealed the allelopathic potential of the water-soluble compounds exuded by the roots of living barley plants. These compounds included saponarin, a flavonoid not yet recognized as a barley root allelochemical.

Antiproliferative and Antimicrobial Activities of Selected Bryophytes

One-hundred and sixty-eight aqueous and organic extracts of 42 selected bryophyte species were screened in vitro for antiproliferative activity on a panel of human gynecological cancer cell lines containing HeLa (cervix epithelial adenocarcinoma), A2780 (ovarian carcinoma), and T47D (invasive ductal breast carcinoma) cells using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and for antibacterial activity on 11 strains using the disc-diffusion method. A total of 99 extracts derived from 41 species exerted ≥25% inhibition of proliferation of at least one of the cancer cell lines at 10 μg/mL. In the cases of Brachythecium rutabulum, Encalypta streptocarpa, Climacium dendroides, Neckera besseri, Pleurozium schreberi, and Pseudoleskeella nervosa, more than one extract was active in the antiproliferative assay, whereas the highest activity was observed in the case of Paraleucobryum longifolium. From the tested families, Brachytheciaceae and Amblystegiaceae provided the highest number of antiproliferative extracts. Only 19 samples of 15 taxa showed moderate antibacterial activity, including the most active Plagiomnium cuspidatum, being active on 8 tested strains. Methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus aureus were the most susceptible to the assayed species. This is the first report on the bioactivities of these 14 species.

C-Glycosyl Flavonoids from Beta vulgaris Cicla and Betalains from Beta vulgaris rubra: Antioxidant, Anticancer and Antiinflammatory Activities-A Review

The green beet (Beta vulgaris var. cicla L.) and red beetroot (B. vulgaris var. rubra L.) contain phytochemicals that have beneficial effects on human health. Specifically, the green beet contains apigenin, vitexin, vitexin-2-O-xyloside and vitexin-2-O-rhamnoside, while the red beetroot is a source of betaxanthins and betacyanins. These phytochemicals show considerable antioxidant activity, as well as antiinflammatory and antiproliferative activities. Vitexin-2-O-xyloside, in combination with betaxanthins and betacyanins, exerts antiproliferative activity in breast, liver, colon and bladder cancer cell lines, through the induction of both intrinsic and extrinsic apoptotic pathways. A significant body of evidence also points to the role of these phytochemicals in the downregulation of the pro-survival genes, baculoviral inhibitor of apoptosis repeat-containing 5 and catenin beta-1, as well as the genes controlling angiogenesis, hypoxia inducible factor 1A and vascular endothelial growth factor A. The multi-target action of these phytochemicals enhances their anticancer activity. Vitexin-2-O-xyloside, betaxanthins and betacyanins can be used in combination with conventional anticancer drugs to reduce their toxicity and overcome the multidrug resistance of cancer cells. In this review, we describe the molecular mechanisms that enable these dietary phytochemicals to block the proliferation of tumor cells and inhibit their pro-survival pathways. Copyright © 2017 John Wiley & Sons, Ltd.

Population structure and genetic diversity in the nannandrous moss Homalothecium lutescens: does the dwarf male system facilitate gene flow?

Background

Nannandry is a sexual system where males (”dwarf males”) are much smaller than the conspecific females. Dwarf males occur in a wide range of unrelated organisms but the evolutionary advantages of this condition are poorly understood. The dwarf male sexual system results in differences in the mode of dispersal and establishment as well as the life span between males and females. Such differences must have profound effects on the population dynamics and genetic structures. We have studied four populations of the nannandrous moss Homalothecium lutescens in southern Sweden. We genotyped dwarf males and female shoots with the aim of describing the genetic diversity and structure of the populations.

Results

Dwarf males were most related to their host shoot, then their colony (within 0.5 m²) and then the rest of the population, which suggests restricted spore dispersal. However, a few dwarf males in each population appeared to originate from other colonies and sometimes even other populations. Genetic diversity of dwarf males was generally high but showed no tendency to be consistently higher or lower than female genetic diversity within the four populations.

Conclusions

Although most dwarf males have local origin, sporadic dispersal events occur. The ability of the dwarf males to establish in high numbers in mature colonies facilitates gene flow between populations as well as increases the potential to accumulate genetic diversity within populations.

Balance between inbreeding and outcrossing in a nannandrous species, the moss Homalothecium lutescens

Epiphytic dwarf males on the females present a possible solution to the problem of short fertilization distances in mosses. However, leptokurtic spore dispersal makes dwarf males likely to be closely related to their host shoot, with an accompanying risk of inbreeding. The capacity of a female to harbour a high number of different dwarf males suggests that there may be mechanisms in place that counteract inbreeding, such as polyandry and post-fertilization selection. We have genotyped sporophytes, female host shoots and dwarf males in four populations of the moss Homalothecium lutescens. We found no evidence of selective sporophyte abortion based on level of heterozygosity. The occurrence of entirely homozygous sporophytes together with significantly positive inbreeding coefficients in three of the populations (mean FIS between 0.48 and 0.64) suggest frequent mother-son mating events. However, 23% of all sampled sporophytes had a higher level of heterozygosity compared with the mean expected heterozygosity at the population level. Polyandry was frequent, on average 59% of the sporophytes on a female shoot were sired by distinct fathers. In conclusion, sporadic fertilizations by dwarf males originating from nonhost female shoots appear to counteract strong inbreeding.

Polytrichum commune L.ex Hedw ethyl acetate extract-triggered perturbations in intracellular Ca²⁺ homeostasis regulates mitochondrial-dependent apoptosis

ETHNOPHARMACOLOGICAL RELEVANCE

Polytrichum commune L.ex Hedw (PCLH), a moss of Bryopsida, has been used as a traditional Chinese medicine and shown to possess anticancer activities. Previous studies have indicated its anti-leukemia effect but the potential mechanisms have not been fully explained.

AIM OF THE STUDY

The present study aimed to further investigate the efficacy of PCLH ethyl acetate fraction (PC-EEF) and the associated mechanisms in human leukemia cells.

MATERIALS AND METHODS

Phytochemical analysis of PC-EEF was performed by spectrophotometry and HPLC. MTT analysis and trypan blue exclusion assay were adopted to examine its cytotoxicity on a panel of leukemia cells (K562, U937, HL-60 and K562/DOX cells) and non-cancerous cells (human PBMCs). Anti-proliferative effect was monitored by colony formation assay and EdU incorporation assay. Ultrastructural alterations on K562 cell membrane surface were observed by scanning electron microscopy. Changes on plasma membrane integrity, cell membrane potential, mitochondrial membrane potential and apoptosis were analyzed by flow cytometry. Fluorescence microscope was performed to assess [Ca(2+)]i level, mitochondrial injury and cytochrome c release. Apoptosis-associated protein expression was analyzed by western blot. The role of Ca(2+) in PC-EEF-induced cell death was investigated by Ca(2+) chelating reagent BAPTA-AM.

RESULTS

PC-EEF possessed relatively high flavonoid content (about 88.84 ± 0.89%) and showed significant cytotoxicity to human leukemia cells. PC-EEF could cause obvious cell morphological deformation, membrane integrity loss and membrane depolarization. Meanwhile, PC-EEF treatment could dramatically potentiate perturbations in cellular Ca(2+) homeostasis. Subsequently, mitochondrial membrane potential (MMP) collapse, cytochrome c release and Bcl-2/Bax down-regulation were all observed. Consistent with these results, PC-EEF treatment resulted in significant activation of caspase 3, poly (ADP-ribose) polymerase (PARP) degradation and apoptosis. Moreover, PC-EEF-caused cytotoxicity, membrane damage, mitochondrial injury and apoptosis were remarkably reversed by BAPTA-AM.

CONCLUSIONS

PC-EEF damaged the membrane system and triggered Ca(2+)-dependent mitochondrial apoptosis, which may provide some new insights into its efficacy against human leukemia cells.

Selective spore germination on shoots of Homalothecium lutescens, a moss with dwarf males

Spores from three bryophyte species with dwarf males (Homalothecium lutescens, Homalothecium sericeum and Isothecium alopecuroides) were sown on shoots of H. lutescens in vitro. After 10 months, presence and fertility of dwarf plants were scored. Spores of the more distantly related I. alopecuroides were unable to develop into dwarf plants on H. lutescens. Spores of both H. lutescens and H. sericeum developed into dwarf plants. In fact, dwarf plants of H. sericeum were both more abundant and more often fertile than those of H. lutescens. The ability of H. sericeum spores to develop into dwarf males on shoots of H. lutescens suggests a possible pathway for hybridization between the two species. On the other hand, the inability of I. alopecuroides to develop into dwarf males on shoots of H. lutescens suggests that regulation of spore germination and dwarf male development on host shoots is associated with the degree of relatedness between species.

Starch hydrolase inhibitors from edible plants

Type 2 diabetes is a chronic disease with gradual deterioration in glucose metabolism, which causes multiple systemic complications. Postprandial hyperglycemia is a concern in the management of type 2 diabetes. Of all the available antidiabetic therapeutic methods, inhibition of α-glucosidase and α-amylase is postulated to be a preventive treatment. Many natural products and herbal medicines have been recommended as being beneficial for mitigation of postprandial hyperglycemia. In this review, recent discoveries of α-glucosidase and α-amylase inhibitors from edible plants are described along with their chemical structures. Their inhibition mechanisms, the type of each glucosidase and amylase, and measurement methods for the inhibitory activity are also given. Finally, recent progress on low glycemic index foods incorporated with plants containing starch hydrolase inhibitors is summarized.

A P450-centric view of plant evolution

Being by far the largest family of enzymes to support plant metabolism, the cytochrome P450s (CYPs) constitute an excellent reporter of metabolism architecture and evolution. The huge superfamily of CYPs found in angiosperms is built on the successful evolution of 11 ancestral genes, with very different fates and progenies. Essential functions in the production of structural components (membrane sterols), light harvesting (carotenoids) or hormone biosynthesis kept some of them under purifying selection, limiting duplication and sub/neofunctionalization. One group (the CYP71 clan) after an early trigger to diversification, has kept growing, producing bursts of gene duplications at an accelerated rate. The CYP71 clan now represents more than half of all CYPs in higher plants. Such bursts of gene duplication are likely to contribute to adaptation to specific niches and to speciation. They also occur, although with lower frequency, in gene families under purifying selection. The CYP complement (CYPomes) of rice and the model grass weed Brachypodium distachyon have been compared to view evolution in a narrower time window. The results show that evolution of new functions in plant metabolism is a very long-term process. Comparative analysis of the plant CYPomes provides information on the successive steps required for the evolution of land plants, and points to several cases of convergent evolution in plant metabolism. It constitutes a very useful tool for spotting essential functions in plant metabolism and to guide investigations on gene function.

Allelopathy of the moss Rhynchostegium pallidifolium and 3-hydroxy-β-ionone

The moss Rhynchostegium pallidifolium (Mitt.) A. Jaeger, which often forms large pure colonies on soils and rocks, inhibited the hypocotyls and root growth of cress (Lepidium sativum L.) seedlings when R. pallidifolium and cress were incubated to-gether on agar medium. The inhibition of cress was greater at the close position from the moss than at the far position from the moss. 3-Hydroxy-β-ionone was found in the medium and concentration of 3-hydroxy-β-ionone in the medium was greater at the close position than at the far position from R. pallidifolium, suggesting that R. pallidifolium may secrete 3-hydroxy-β-ionone into the medium. Exogenously ap-plied 3-hydroxy-β-ionone inhibited the growth of hypocotyls and roots of cress at con¬cen¬tra¬tions greater than 1 and 3 μM, respectively. Considering the growth inhibi-tory activity and concentrations found in the medium, 3-hydroxy-β-ionone was esti-mated to be able to cause 46 - 64 % of the observed growth inhibition of cress hypo-cotyls and roots by R. pallidifolium. Therefore, 3-hydroxy-β-ionone may play an important role in the allelopathic activity of R. pallidifolium and may help competi-tion with neighboring plants resulting in the formation of pure colonies.

Genome-wide analysis of the chalcone synthase superfamily genes of Physcomitrella patens

Enzymes of the chalcone synthase (CHS) superfamily catalyze the production of a variety of secondary metabolites in bacteria, fungi and plants. Some of these metabolites have played important roles during the early evolution of land plants by providing protection from various environmental assaults including UV irradiation. The genome of the moss, Physcomitrella patens, contains at least 17 putative CHS superfamily genes. Three of these genes (PpCHS2b, PpCHS3 and PpCHS5) exist in multiple copies and all have corresponding ESTs. PpCHS11 and probably also PpCHS9 encode non-CHS enzymes, while PpCHS10 appears to be an ortholog of plant genes encoding anther-specific CHS-like enzymes. It was inferred from the genomic locations of genes comprising it that the moss CHS superfamily expanded through tandem and segmental duplication events. Inferred exon-intron architectures and results from phylogenetic analysis of representative CHS superfamily genes of P. patens and other plants showed that intron gain and loss occurred several times during evolution of this gene superfamily. A high proportion of P. patens CHS genes (7 of 14 genes for which the full sequence is known and probably 3 additional genes) are intronless, prompting speculation that CHS gene duplication via retrotransposition has occurred at least twice in the moss lineage. Analyses of sequence similarities, catalytic motifs and EST data indicated that a surprisingly large number (as many as 13) of the moss CHS superfamily genes probably encode active CHS. EST distribution data and different light responsiveness observed with selected genes provide evidence for their differential regulation. Observed diversity within the moss CHS superfamily and amenability to gene manipulation make Physcomitrella a highly suitable model system for studying expansion and functional diversification of the plant CHS superfamily of genes.

Suppression of bacterial cell-cell signalling, biofilm formation and type III secretion system by citrus flavonoids

AIM

This study investigated the quorum sensing, biofilm and type three secretion system (TTSS) inhibitory properties of citrus flavonoids.

METHODS AND RESULTS

Flavonoids were tested for their ability to inhibit quorum sensing using Vibrio harveyi reporter assay. Biofilm assays were carried out in 96-well plates. Inhibition of biofilm formation in Escherichia coli O157:H7 and V. harveyi by citrus flavonoids was measured. Furthermore, effect of naringenin on expression of V. harveyi TTSS was investigated by semi-quantitative PCR. Differential responses for different flavonoids were observed for different cell-cell signalling systems. Among the tested flavonoids, naringenin, kaempferol, quercetin and apigenin were effective antagonists of cell-cell signalling. Furthermore, these flavonoids suppressed the biofilm formation in V. harveyi and E. coli O157:H7. In addition, naringenin altered the expression of genes encoding TTSS in V. harveyi.

CONCLUSION

The results of the study indicate a potential modulation of bacterial cell-cell communication, E. coli O157:H7 biofilm and V. harveyi virulence, by flavonoids especially naringenin, quercetin, sinensetin and apigenin. Among the tested flavonoids, naringenin emerged as potent and possibly a nonspecific inhibitor of autoinducer-mediated cell-cell signalling. Naringenin and other flavonoids are prominent secondary metabolites present in citrus species. Therefore, citrus, being a major source of some of these flavonoids and by virtue of widely consumed fruit, may modulate the intestinal microflora.

SIGNIFICANCE AND IMPACT OF THE STUDY

Currently, a limited number of naturally occurring compounds have demonstrated their potential in inhibition of cell-cell communications; therefore, citrus flavonoids may be useful as lead compounds for the development of antipathogenic agents.

Secondary metabolites in bryophytes: an ecological aspect

Bryophytes frequently grow in an unfavorable environment as the earliest land plants, and inevitably biosynthesize secondary metabolites against biotic or abiotic stress. They not only defend against the plant competition, microbial attack, and insect or animal predation, but also function in UV protection, drought tolerance, and freezing survival. This review covers the ecological aspect of secondary metabolites in bryophytes and is taxonomically presented according to the ecological significances.

Microbial metabolism part 9. Structure and antioxidant significance of the metabolites of 5,7-dihydroxyflavone (chrysin), and 5- and 6-hydroxyflavones

5,7-Dihydroxyflavone (chrysin) (1) when fermented with fungal cultures, Aspergillus alliaceous (ATCC 10060), Beauveria bassiana (ATCC 13144) and Absidia glauco (ATCC 22752) gave mainly 4'-hydroxychrysin (4), chrysin 7-O-beta-D-4-O-methylglucopyranoside (5) and chrysin 7-sulfate (6), respectively. Mucore ramannianus (ATCC 9628), however, transformed chrysin into six metabolites: 4'-hydroxy-3'-methoxychrysin (chrysoeriol) (7), 4'-hydroxychrysin (apigenin) (4) 3',4'-dihydroxychrysin (luteolin) (8), 3'-methoxychrysin 4'-O-alpha-D-6-deoxyallopyranoside (9), chrysin 4'-O-alpha-D-6-deoxyallopyranoside (10), and luteolin 3'-sulfate (11). Cultures of A. alliaceous (ATCC 10060) and B. bassiana (ATCC 13144) metabolized 5-hydroxyflavone (2) into 5,4'-dihydroxyflavone (12) and 4'-hydroxyflavone 5-O-beta-D-4-O-methylglucopyranoside (13), respectively. 6-Hydroxyflavone (3) was transformed into 6-hydroxyflavanone (14), flavone 3-O-beta-D-4-O-methylglucopyranoside (15) and (+/-)-flavanone 6-O-beta-D-4-O-methylglucopyranoside (16) by cultures of Beauveria bassiana (ATCC 13144). The structures of the metabolic products were elucidated by means of spectroscopic data. The significance of the metabolites as antioxidants in relation to their structure is briefly discussed.

Exudation of allelopathic substances in buckwheat (Fagopyrum esculentum Moench)

Root exudates of the common buckwheat, especially phenolic compounds, were studied. Their contents, both in the soil during the growing season and in agar medium during germination, were determined by HPLC and GC-MS. The allelopathic activity of the soil from a buckwheat stand was evaluated, as well. Palmitic acid, squalene, epicatechin, vitexin, a gallic acid derivative, and a quercetin derivative were the main compounds of the agar medium. In the soil, palmitic acid methyl ester, vanillic acid, rutin, a gallic acid derivative, and a 4-hydroxyacetophenone derivative were identified. The effects of vitexin, squalene, epicatechin, 4-hydroxyacetophenone, and vanillic and gallic acids were tested on eight plant species. Inhibitive effects were observed in the cases of 4-hydroxyacetophenone and vanillic and gallic acids. Comparisons of the identified compounds and inhibitive effects of soil extracts indicated that palmitic acid and the gallic acid derivative probably have an important function in the allelopathic root response of buckwheat.

Phytogrowth-inhibitory and antibacterial activity of Verbascum sinuatum

The methanolic extract of Verbascum sinuatum inflorescences and isolated compounds were tested for their antibacterial activity against 13 Gram(+) and Gram(-) bacteria and for their allelopathic activity against radish.

Cloning and characterization of chalcone synthase from the moss, Physcomitrella patens

Since the early evolution of land plants from primitive green algae, flavonoids have played an important role as UV protective pigments in plants. Flavonoids occur in liverworts and mosses, and the first committed step in the flavonoid biosynthesis is catalyzed by chalcone synthase (CHS). Although higher plant CHSs have been extensively studied, little information is available on the enzymes from bryophytes. Here we report the cloning and characterization of CHS from the moss, Physcomitrella patens. Taking advantage of the available P. patens EST sequences, a CHS (PpCHS) was cloned from the gametophores of P. patens, and heterologously expressed in Escherichia coli. PpCHS exhibited similar kinetic properties and substrate preference profile to those of higher plant CHS. p-Coumaroyl-CoA was the most preferred substrate, suggesting that PpCHS is a naringenin chalcone producing CHS. Consistent with the evolutionary position of the moss, phylogenetic analysis placed PpCHS at the base of the plant CHS clade, next to the microorganism CHS-like gene products. Therefore, PpCHS likely represents a modern day version of one of the oldest CHSs that appeared on earth. Further, sequence analysis of the P. patens EST and genome databases revealed the presence of a CHS multigene family in the moss as well as the 3'-end heterogeneity of a CHS gene. Of the 19 putative CHS genes, 10 genes are expressed and have corresponding ESTs in the databases. A possibility of the functional divergence of the multiple CHS genes in the moss is discussed.

Antibacterial and allelopathic activity of methanolic extract from Iris pseudopumila rhizomes

The methanolic extract of rhizomes of Iris pseudopumila was tested for its antibacterial and allelopathic activity. The extract was shown to have antibacterial effects. The allelopathic effect was tested against Raphanus sativus seed germination. The extract caused a decrease in the percentage of seed germination and root and epicotyl growth.

Total synthesis of three naturally occurring 6,8-di-C-glycosylflavonoids: phloretin, naringenin, and apigenin bis-C-beta-D-glucosides

Three naturally occurring di-C-glycosylflavonoids, phloretin (dihydrochalcone), naringenin (flavanone), and apigenin (flavone) bis-6,8-C-beta-D-glucopyranosides (4, 5, and 6), were synthesized in total yields of 52.3%, 53.5%, and 36.4%, respectively, starting from the key compound, di-C-beta-D-glucopyranosylphloroacetophenone (1). Benzyl protection of the phenolic hydroxyls in 1 and a subsequent aldol condensation with benzyloxybenzaldehyde led to the production of chalcone 3, which, after hydrogenolysis or acid hydrolysis and deprotection, gave 4 and 5, respectively. The acetylation of 5, followed by DDQ oxidation and deprotection, gave 6.

Flavones and flavone synthases

Within the secondary metabolite class of flavonoids which consist of more than 9000 known structures, flavones define one of the largest subgroups. Their natural distribution is demonstrated for almost all plant tissues. Various flavone aglyca and their O- or C-glycosides have been described in the literature. The diverse functions of flavones in plants as well as their various roles in the interaction with other organisms offer many potential applications, not only in plant breeding but also in ecology, agriculture and human nutrition and pharmacology. In this context, the antioxidative activity of flavones, their use in cancer prevention and treatment as well as the prevention of coronary heart disease should be emphasized. The therapeutic potential of flavones makes these compounds valuable targets for drug design, including recombinant DNA approaches. The biosynthesis of flavones in plants was found to be catalyzed by two completely different flavone synthase proteins (FNS), a unique feature within the flavonoids. The first, FNS I, a soluble dioxygenase, was only described for members of the Apiaceae family so far. The second, FNS II, a membrane bound cytochrome P450 enzyme, has been found in all other flavone accumulating tissues. This phenomenon is particularly of interest from the evolutionary point of view concerning the flavone biosynthesis and functions in plants. Recently, FNS I and FNS II genes have been cloned from a number of plant species. This now enables detailed biochemical and molecular characterizations and also the development of direct metabolic engineering strategies for modifications of flavone synthesis in plants to improve their nutritional and/or biopharmaceutical value.

Flavonoids from shoots, roots and roots exudates of Brassica alba

Analysis of extracts obtained from shoots, roots and exudates of Brassica alba revealed the presence of 3,5,6,7,8-pentahydroxy-4'-methoxy flavone in shoots, as well as 2',3',4',5',6'-pentahydroxy chalcone and 3,5,6,7,8-pentahydroxy flavone in roots and exudates. Apigenin was also found in the shoots and roots, but not in the root exudates.