Barbara Soldo

Chemical Composition and Biological Activity of Allium cepa L. and Allium × cornutum (Clementi ex Visiani 1842) Methanolic Extracts

Here, we report a comparative study of the phytochemical profile and the biological activity of two onion extracts, namely Allium cepa L. and Allium × cornutum (Clementi ex Visiani 1842), members of the family Amaryllidaceae. The identification of flavonoids and anthocyanins, and their individual quantities, was determined by high-performance liquid chromatography (HPLC). The potency of both extracts to scavenge free radicals was determined by the DPPH (2,2′-diphenyl-1-picrylhydrazyl) radical-scavenging activity and oxygen radical absorbance capacity (ORAC) methods. The DNA protective role was further tested by the single-cell gel electrophoresis (COMET) assay and by Fenton’s reagent causing double-strand breaks on the closed circular high copy pUC19 plasmid isolated from Escherichia coli. In the presence of both extracts, a significant decrease in DNA damage was observed, which indicates a protective role of Allium cepa and Allium × cornutum on DNA strand breaks. Additionally, cytotoxicity was tested on glioblastoma and breast cancer cell lines. The results showed that both extracts had antiproliferative effects, but the most prominent decrease in cellular growth was observed in glioblastoma cells.

The A9 Core Sequence from NRPS Adenylation Domain Is Relevant for Thioester Formation

The adenylation (A) domain in nonribosomal peptide synthetases catalyses a two‐step reaction in which an amino acid is activated and then transferred to the neighbouring thiolation (T) domain. In this study, we investigated the role of the conserved A9 core sequence of the A‐domain of tyrocidine synthetase 1, by analysis of single amino acid mutations in the A9 region. Mutation of an absolutely conserved proline (P490G) significantly reduced the conformational stability of the protein, as evidenced by increased susceptibility to proteolytic cleavage and denaturation. All mutant A‐domains were capable of amino acid activation, but the activity in the overall reaction was reduced. Surprisingly, the S491R mutant (mutation at the first residue following the A9 motif) showed elevated overall activity compared to the wild‐type protein. Our results suggest that the A9 core sequence plays a role in the second reaction step, in which it could serve as a “clip” for the proper positioning of residues important for the interaction with the T‐domain, and/or stabilisation of the thioester‐forming conformation.

Evaluation of Olive Fruit Lipoxygenase Extraction Protocols on 9- and 13-Z,E-HPODE Formation

In plant tissues, enzymes implicated in the lipoxygenase (LOX) pathway are responsible for the hydroperoxydation of polyunsaturated fatty acids, ultimately leading to the production of small chemical species involved in several physiological processes. During industrial olive oil production, these enzymes are activated upon crushing and grinding of olive fruit tissue, subsequently leading to the synthesis of volatile compounds responsible for the positive aroma and flavor of the oil. An investigation of LOX activity during olive fruit ripening and malaxation could assist in the production of oils with favorable aroma and taste. Therefore, a reliable method for olive LOX purification is crucial. Here we report a critical review of six LOX extraction protocols, two of which have shown minimum enzyme activity, possibly leading to misconceptions in the interpretation of experimental data. Future research concerning olive LOX should employ extraction methods that preserve enzyme activity.

Manganese soil and foliar fertilization of olive plantlets: the effect on leaf mineral and phenolic content and root mycorrhizal colonization: Manganese soil and foliar fertilization of olive plantlets

BACKGROUND The present study aimed to examine the effect of foliar (Mn_fol) and soil Zeolite-Mn (Mn_ZA) application on leaf mineral, total phenolic and oleuropein content, and mycorrhizae colonization of self-rooted cv. Leccino plantlets grown on calcareous soil. RESULTS The dissolution of zeolite was 97% when citric acid was applied at 0.05 mM dm-3 , suggesting that organic acids excreted by roots can dissolve modified zeolite (Mn_ZA), making Mn available for plant uptake. The leaf Mn concentration was the highest for Mn_fol treatment at 90 days after transplanting (DAT) (172 mg kg-1 ) and 150 DAT (70 mg kg-1 ) compared to other treatments. Mn_ZA soil application increased leaf Mn concentration at 150 DAT compared to control and NPK treatments. The oleuropein leaf content was highest for Mn_fol compared to other treatments at 90 DAT and lowest at 150 DAT. Arbuscular mycorrhizal colonization was higher for Mn_fol treatment at 150 DAT compared to all other treatments. CONCLUSION Changes in the arbuscular colonization percentage and oleuropein content may be connected to stress conditions provoked by a high leaf Mn concentration in the Mn_fol treatment at 90 DAT. Mn_ZA application increased leaf Mn concentration at 150 DAT compared to control and NPK treatments. It can be assumed that the dominant mechanism in Mn uptake from modified zeolite is Mn_ZA dissolution through root exudates.

Quaternary salts derived from 3-substituted quinuclidine as potential antioxidative and antimicrobial agents

Abstract Two series of novel ammonium salts containing the quinuclidine moiety were prepared in order to evaluate their antioxidative, antibacterial and antifungal potential. The synthesized homologues of 3-hydroxy (QOH) and 3-chloroquinuclidine (QCl) with the different N-benzyl substituents at the para-position (bromo, chloro or nitro group) were obtained in very good yields and characterized by IR and NMR spectroscopies and elemental analysis. All compounds were tested for antioxidative activity using the oxygen radical absorbance capacity (ORAC) assay and among tested samples, N-p-nitrobenzyl-3-hydroxyquinuclidinium bromide (QOH-4) exhibited the highest antioxidative potential (293.80 nmol (TE) mL-1), which was further investigated by the DNA nicking assay. The biological activity of selected compounds was evaluated by measuring the zone of inhibition and by determining the minimal inhibitory concentration (MIC) against three Gram-positive bacteria (B. cereus, E. faecalis and S. aureus), three Gram-negative bacteria (E. coli, P. aeruginosa and C. sakazakii) and three fungi species (C. albicans, A. niger and P. notatum). The bioactivity assay showed that some newly synthetized quaternary quinuclidinium compounds display a comparable or even better antibacterial and antifungal activity than the reference drugs such as gentamicin (GEN), cefotaxime (CTX) and amphotericin B (AMPHB). Among the tested compounds, N-p-chlorobenzyl-3-hydroxyquinuclidinium bromide (QOH-3) exhibited a considerable antibacterial efficiency against P. aeruginosa (MIC=0.39 µg mL-1) and QOH-4 displayed a potent antifungal activity against C. albicans (MIC=1.56 µg mL-1).