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Effect of chitosan oligosaccharides and other biotic elicitors on root cultures and in vitrogrown plantlets systems of Hypericum perforatum L.
No full textHypericum perforatum is one of the most studied medicinal plants due to its demonstrated antidepressant,
anticancer and antimicrobial properties (1) and it has been used for centuries in popular medicine. Its most
well-known metabolites, hypericin and hyperforin, are extracted from the aerial part of the plant (2, 3).
Although many therapeutic properties of aerial parts have been extensively studied, little information is
available on the chemical composition and biological activity of root extracts. Recently, we focused on
bioactive metabolites accumulated in the root, with particular interest for xanthones. These compounds
exhibit numerous pharmacological activities, including antifungal (4 and references therein), antiradical and
anti-inflammatory (5).
Xanthones are non-flavonoid phenolic compounds produced by some plants, fungi, lichens and bacteria. As
all the other phenols, they are synthesized through the phenylpropanoid biosynthetic pathway.
In H. perforatum root, xanthones are accumulated at very low levels, which are not adequate for large-scale
production (4). In vitro roots exhibit a higher content in xanthones and the production could be enhanced by
treating them with both biotic and abiotic elicitors. In previous works, we demonstrated that chitosan is the
most effective elicitor in increasing xanthone production in H. perforatum root cultures. This is a
polysaccharide obtained by partial deacetylation of chitin, the main structural element of arthropod
exoskeleton and of cell walls in fungi. One of the problems related to the use of chitosan is its insolubility in
water at neutral pH and in other organic solvents; therefore it is generally dissolved in water acidulated with
acetic acid. Although this does not limit its use for application purposes, it makes difficult to discriminate the
effect of chitosan from that of its solvent, and consequently its use to determine elicitation mechanisms (4).
Recently, chitosan oligosaccharides (COS), obtained through chemical or enzymatic hydrolysis of chitosan,
have gained interest for their high water-solubility at neutral pH, low viscosity, biodegradability,
biocompatibility and non-toxicity (6). These features make COS promising elicitors both for application
purposes and basic search.
This research aims to evaluate the effects of chitosan oligosaccharides (COS) both on in vitro root cultures of
H. perforatum and in vitro-grown plants. Chemical analyses have been conducted on both systems to
compare their elicitor-responsivity to COS in term of xanthone production. The experiments have been
carried out on in vitro-grown plantlets with elicitors such as jasmonates and salicylic acid, which in previous
tests resulted ineffective on in vitro cultures of regenerated roots, to verify if shoot organs are involved in the
perception of elicitors. The impact of elicitor treatments was evaluated not only in relation of root-specific
metabolites (e.g. xanthones), but also on shoot-specific metabolites (e.g. hypericin and hyperforin).
Further investigations regarded the expression, in COS-elicited root cultures, of genes involved in the
biosynthetic polyphenols pathway, namely phenylalanine ammonia lyase (PAL), benzophenone synthase
(BPS) and chalcone synthase (CHS). Previous results shown an antagonistic relationship between genes
involved in the biosynthesis of chalcones (mainly flavonoids) and benzophenones (mainly xanthones),
suggesting a common gene-regulation system, in agreement with (7)
Water-soluble chitooligosaccharides (COS) elicit xanthone biosynthesis in Hypericum perforatum root cultures
No full textHypericum perforatum L. (Hypericaceae), popularly known as St. John’s wort, is a medicinal plant widely used in folk medicine since ancient times, with a long list of medicinal uses. Most of the research on St. John’s wort has been focused on the aerial organs of the plant, and only recently the root has been recognized as an attractive source of secondary metabolites of pharmacological interest [1]. The root of H. perforatum contains xanthones, although at very low levels [2;3]. Xanthones are a wide and structurally diverse group of polyphenol with several pharmacological properties [4]. We have recently demonstrated that H. perforatum root cultures constitutively produce xanthones at higher levels than the root of the plant and that they respond to chitosan (CHIT) elicitation with a noteworthy increase in xanthone production. Among elicitors, CHIT is one of the most used to increase the biosynthesis of plant phytoalexins, including xanthones. However, CHIT is insoluble in neutral water as well as in most organic solvents, therefore, it is commonly dissolved in water acidulated with acetic acid [5], which greatly limits its application. Furthermore we recently demonstrated that acetic acid strongly affect xanthone biosynthesis, altering the effect of CHIT [5]. To overcome these problems, in this study, water-soluble oligosaccharides obtained through enzymatic digestion and deacetylation of chitosan have been tested. Initially, chitooligosaccharides (COS) have been administered to the root cultures following the same protocols used for CHIT elicitation. Fifteen days after the addition with COS a 100% increase in the production of total xanthones was obtained (from 4.4 to 9.8 mg/g DW). The most represented xanthones were paxanthone and 5-O-methyl-2 deprenylrheediaxanthone B. Additional experiments were carried out to optimize the elicitation protocol with COS. In particular, it was tested the effect of different concentrations of COS (from 50 to 800 mg/l) and the residence time of the elicitor in the culture medium (from 5 to 25 days). The best results were obtained with 400 mg/l COS and with 25 days of residence time (530% xanthone increase). The antifungal activity of the methanol extracts of roots treated with COS was evaluated on several human pathogenic fungi, including Candida albicans, Microsporum gypseum and Trichophyton mentagrophytes. Several extracts showed interesting MIC values (16-64), suggesting a possible use as antifungal agents. Gene expression studies are in progress to evaluate the contribution of some key genes in polyphenol biosynthesis, such as phenylalanine ammonia lyase (PAL, involved in the biosynthesis of all phenols), chalcone synthase (CHS, involved in both xanthones and flavonoids) and benzefenone synthase (BPS, specifically involved in xanthone biosynthesis). Preliminary results on COS-elicited roots shown a sub-expression of PAL and an overexpression of BPS, while the CHS expression does not shown significant alterations with respect to the control roots
IN VITRO ROOT CULTURES OF DIFFERENT HYPERICUM SPECIES: A PROMISING SYSTEM FOR THE PRODUCTION OF ANTIFUNGAL XANTHONE-RICH EXTRACTS
No full textAcetic acid acts as an elicitor exerting a chitosan-like effect on xanthone biosynthesis in Hypericum perforatum L. root cultures
No full textHypericum perforatum L. (Hypericaceae), popularly known as St. John’s wort, is a medicinal plant widely used in folk medicine [1]. It is known mainly for its antidepressant activity, and nowadays St. John’s wort preparations are among the most widely prescribed drugs for depression in many European countries [2]. Since the secondary metabolites responsible for the antidepressant activity (e.g. hyperforins and hypericins) are mainly accumulated in leaves and flowers, the chemical composition and the medicinal properties of aerial parts have been extensively investigated [3]. Differently the root has been poorly studied and only recently it has been recognized as an attractive source of bioactive secondary metabolites [4]. We have recently demonstrated that H. perforatum root cultures constitutively produce xanthones at higher levels than the root of the plant and that they respond to chitosan (CHIT) elicitation with a significant increase in xanthone production [5]. Xanthones are a wide and structurally diverse group of polyphenols produced by a restricted number of plants, fungi, lichens, and bacteria with multiple bioactivities [6]. In the present study, CHIT was administered to H. perforatum root cultures using three different elicitation protocols, and the increase in xanthone production was evaluated through HPLC. The best results (550 % xanthone increase) were obtained by subjecting the roots to a single elicitation with 200 mg l-1 CHIT and maintaining the elicitor in the culture medium for 1 week. To discriminate the effect of CHIT from that of the solvent, control experiments were performed by administering acetic acid alone at the same concentration used for CHIT solubilization. Unexpectedly, acetic acid caused an increase in xanthone production comparable to that observed in response to CHIT. Feeding experiments with 13C-labeled acetic acid demonstrated that this compound is not incorporated into the xanthone skeleton. Other short-chain monocarboxylic acids (i.e. propionic and butyric acid) had little or no effect on the production of xanthones. These results indicate that acetic acid acts as a specific signal molecule, able to significantly enhance xanthone biosynthesis in H. perforatum root cultures
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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