Antioxidant response in Chenopodium album elicited by Ascochyta caulina mycoherbicide phytotoxins

Antioxidant defence responses were evaluated in Chenopodium album plants treated with a mixture of the phytotoxins ascaulitoxin, 2,4,7-triamino-5-hydroxyoctandioic acid (ascaulitoxin aglycone) and trans-4-aminoproline, produced by the pathogenic fungus Ascochyta caulina, previously proposed as mycoherbicide for this noxious weed. The enzymatic and non-enzymatic effects of these phytotoxins on the ascorbate system and on catalase activity were assessed by evaluating their biological and specific activities through spectrophotometric and electrophoretic analyses. In addition, the oxidative status was monitored through evaluating H2O2 content during the time-course. The mixture of toxins induced high levels of H2O2 accumulation resulting in an oxidative burst in the plant cells. Ascorbate peroxidase and catalase had crucial roles in detoxifying H2O2. The persisting metabolic perturbations, however, led to severe necrosis and death of C. album plants. The induced H2O2 production may be generated by the fungus as part of its necrotrophic nature. This study explains the defence responses in C. album to the mycoherbicide, in particular, the ascorbate systems’ components and H2O2 as an index of oxidative stress

Phytotoxins produced by Pestalotiopsis guepinii, the causal agent of hazelnut twig blight

The main lipophilic phytotoxic metabolite was isolated from the culture filtrates of Pestalotiopsis guepinii, the fungus causing twig blight of hazelnut. The metabolite was spectroscopically identified as pestalopyrone, a pentaketide that it was originally identified as a minor toxin produced by Pestalotiopsis oenotherae. The toxic activity of pestalopyrone was compared with that of nectriapyrone, a structurally related monoterpenoid recently isolated from Phomopsis foeniculi, and that of the new dihydro-derivative of nectriapyrone. The high phytotoxic activity of nectriapyrone and its dihydro-derivative on three non host  plants, showed that the double bond of the 1-methylpropenyl group at C-6 of the aromatic ring is inessential for its activity, while the much lower activity of pestalopyrone showed that the methyl group at C-3 of the same ring is an important structural feature. The high molecular weight hydrophilic phytotoxins produced by this fungus are reported for the first time

Higginsianins A and B, Two Diterpenoid α-Pyrones Produced by Colletotrichum higginsianum, with in Vitro Cytostatic Activity

Two new diterpenoid α-pyrones, named higginsianins A (1) and B (2), were isolated from the mycelium of the fungus Colletotrichum higginsianum grown in liquid culture. They were characterized as 3-[5a,9b-dimethyl-7-methylene-2-(2-methylpropenyl)dodecahydronaphtho[2,1-b]furan-6-ylmethyl]-4-hydroxy-5,6-dimethylpyran-2-one and 4-hydroxy-3-[6-hydroxy-5,8a-dimethyl-2-methylene-5-(4-methylpent-3-enyl)decahydronaphthalen-1-ylmethyl]-5,6-dimethylpyran-2-one, respectively, by using NMR, HRESIMS, and chemical methods. The structure and relative configuration of higginsianin A (1) were confirmed by X-ray diffractometric analysis, while its absolute configuration was assigned by electronic circular dichroism (ECD) experiments and calculations using a solid-state ECD/TDDFT method. The relative and absolute configuration of higginsianin B (2), which did not afford crystals suitable for X-ray analysis, were determined by NMR analysis and by ECD in comparison with higginsianin A. 1 and 2 were the C-8 epimers of subglutinol A and diterpenoid BR-050, respectively. The evaluation of 1 and 2 for antiproliferative activity against a panel of six cancer cell lines revealed that the IC50 values, obtained with cells reported to be sensitive to pro-apoptotic stimuli, are by more than 1 order of magnitude lower than their apoptosis-resistant counterparts (1 vs >80 μM). Finally, three hemisynthetic derivatives of 1 were prepared and evaluated for antiproliferative activity. Two of these possessed IC50 values and differential sensitivity profiles similar to those of 1

Antioxidant response in Chenopodium album elicited by Ascochyta caulina mycoherbicide phytotoxins

Antioxidant defence responses were evaluated in Chenopodium album plants treated with a mixture of the phytotoxins ascaulitoxin, 2,4,7-triamino-5-hydroxyoctandioic acid (ascaulitoxin aglycone) and trans-4-aminoproline, produced by the pathogenic fungus Ascochyta caulina, previously proposed as mycoherbicide for this noxious weed. The enzymatic and non-enzymatic effects of these phytotoxins on the ascorbate system and on catalase activity were assessed by evaluating their biological and specific activities through spectrophotometric and electrophoretic analyses. In addition, the oxidative status was monitored through evaluating H2O2 content during the time-course. The mixture of toxins induced high levels of H2O2 accumulation resulting in an oxidative burst in the plant cells. Ascorbate peroxidase and catalase had crucial roles in detoxifying H2O2. The persisting metabolic perturbations, however, led to severe necrosis and death of C. album plants. The induced H2O2 production may be generated by the fungus as part of its necrotrophic nature. This study explains the defence responses in C. album to the mycoherbicide, in particular, the ascorbate systems’ components and H2O2 as an index of oxidative stress

Terpestacin, a toxin produced by Phoma exigua var. heteromorpha, the causal agent of a severe foliar disease of oleander (Nerium oleander L.)

Since 1987, several cytochalasins were isolated from Phoma exigua var. heteromorpha, the causal agent of foliar blight disease of oleander (Nerium oleander L.), and chemically and biologically characterised. During the purification process of a large-scale production of cytochalasins A and B, necessary to continue the study on their anticancer activity, a metabolite having a different carbon skeleton compared to that of cytochalasans, was isolated. It was identified as terpestacin, a well-known toxic fungal stestertepenoid, isolated for the first time from P. exigua var. heteromorpha, by spectroscopic investigation (essentially 1D and 2D 1H and 13C-NMR and ESI MS) and optical methods in comparison with the literature data. Terpestacin and some its derivatives (including a natural one, fusaproliferin) were prepared and tested for their biological activity. Terpestacin and fusaproliferin had some inhibitory effects on seed germination of Phelipanche ramosa, whereas none of the compounds caused phytotoxic effects on weed leaves.[Formula: see text]

Inuloxin A Inhibits Seedling Growth and Affects Redox System of Lycopersicon esculentum Mill. and Lepidium sativum L.

Allelochemicals are considered an environment-friendly and promising alternative for weed management, although much effort is still needed for understanding their mode of action and then promoting their use in plant allelopathy management practices. Here, we report that Inuloxin A (InA), an allelochemical isolated from Dittrichia viscosa, inhibited root elongation and growth of seedlings of Lycopersicon esculentum and Lepidium sativum at the highest concentrations tested. InA-induced antioxidant responses in the seedlings were investigated by analysing the contents of glutathione (GSH) and ascorbate (ASC), and their oxidized forms, dehydroascorbate (DHA), and glutathione disulphide (GSSG), as well as the redox state of thiol-containing proteins. An increase in ASC, DHA, and GSH levels at high concentrations of InA, after 3 and 6 days, were observed. Moreover, the ASC/DHA + ASC and GSH/GSSG + GSH ratios showed a shift towards the oxidized form. Our study provides the first insight into how the cell redox system responds and adapts to InA phytotoxicity, providing a framework for further molecular studies

Antibiotic and Nematocidal Metabolites from Two Lichen Species Collected on the Island of Lampedusa (Sicily)

The antibiotic and nematocidal activities of extracts from two coastal lichen species collected on Lampedusa Island (Sicily), Ramalina implexa Nyl. and Roccella phycopsis Ach., were tested. Methyl orsellinate, orcinol, (+)-montagnetol, and for the first time 4-chlororcinol were isolated from Roccella phycopsis. (+)-Usnic acid was obtained from Ramalina implexa. The crude organic extract of both lichen species showed strong antibiotic activity against some bacterial species and nematocidal activity. Among all the pure metabolites tested against the infective juveniles (J2) of the root-knot nematode (RKN) Meloydogine incognita, (+)-usnic acid, orcinol, and (+)-montagnetol had significant nematocidal activity, comparable with that of the commercial nematocide Velum® Prime, and thus they showed potential application in agriculture as a biopesticide. On the contrary, methyl orsellinate and 4-chlororcinol had no nematocidal effect. These results suggest that the substituent pattern at ortho-para-position in respect to both hydroxyl groups of resorcine moiety, which is present in all metabolites, seems very important for nematocidal activity. The organic extracts of both lichens were also tested against some Gram-positive and Gram-negative bacteria. Both extracts were active against Gram-positive species. The extract of Ramalina implexa showed, among Gram-negative species, activity against Escherichia coli and Acinetobacter baumannii, while that from Roccella phycopsis was effective towards all test strains, with the exception of Pseudomonas aeruginosa. The antimicrobial activity of (+)-usnic acid, methyl orsellinate, and (+)-montagnetol is already known, so tests were focused on orcinol and 4-chlororcinol. The former showed antibacterial activity against all Gram positive and Gram-negative test strains, with the exception of A. baumannii and K. pneumoniae, while the latter exhibited a potent antibacterial activity against Gram-positive test strains and among Gram-negative strains, was effective against A. baumannii and K. pneumonia. These results suggest, for orcinol and 4-chlororcinol, an interesting antibiotic potential against both Gram-positive and Gram-negative bacterial strains