María A. Ponce

Flavonoids exhibit fungal species and genus specific effects on the presymbiotic growth of Gigaspora and Glomus.

The effect of the flavonoids chrysin, isorhamnetin, kaempferol, luteolin, morin and rutin on pre-symbiotic growth, such as spore germination, hyphal length, hyphal branching and the formation of auxiliary cells and secondary spores, of the arbuscular mycorrhizal fungi Gigaspora rosea, G. margarita, Glomus mosseae and G. intraradices was studied. According to the effect on each fungal growth parameter, the tested compounds could be classified to be genus and/or species specific or specific, for a certain developmental stage of pre-symbiotic growth. A clear arbuscular mycorrhizal genus specific, and even species specific, effect of some flavonoids was observed. However, this specificity of a flavonoid could not be generalized but differs depending on the pre-symbiotic stage of the AM fungus. Moreover, our show that for a better understanding of the role of compounds in the AM symbiosis, studies should not be conducted only with one AM fungus looking at one fungal growth parameter such as spore germination or hyphal length, but should be wider, including several growth parameters and several AM fungi.

The effect of flavones and flavonols on colonization of tomato plants by arbuscular mycorrhizal fungi of the genera Gigaspora and Glomus

No clear data are available on how flavonoids from different chemical groups affect root colonization by arbuscular mycorrhizal fungi (AMF) and whether flavonoids affecting the presymbiotic growth of AMF also affect root colonization by AMF. In the present work, we compared the effect of flavones (chrysin and luteolin) and flavonols (kaempferol, morin, isorhamnetin, and rutin) on root colonization (number of entry points and degree of root colonization) of tomato plants (Lycopersicum esculentum L.) with the effect of these flavonoids on the presymbiotic growth of these AMF, which has been reported in a recent study. With all tested AMF (Gigaspora rosea, Gigaspora margarita, Glomus mosseae, and Glomus intraradices) a correlation between the number of entry points and the percentage of root colonization was found. When the number of entry points was high, root colonization was also enhanced. Application of the flavones chrysin and luteolin and of the flavonol morin increased the number of entry points and the degree of colonization,whereas the flavonols kaempferol, isorhamnetin, and rutin showed no effect. These results show that in contrast to their effect on the presymbiotic growth of the AMF on the level of root colonization, the tested flavonoids do not exhibit a genus- and species-specificity. Moreover, comparison of our data with the data obtained by J.M. Scervino, M.A. Ponce, R. Erra-Bassells, H. Vierheilig, J.A. Ocampo, and A. Godeas. (2005a. J. Plant Interact. 15: 22-30) indicates that a positive effect on the hyphal growth of AMF does not necessarily result in an enhanced AM root colonization, further indicating that the mode of action of flavonoids at the level of root colonization is more complex.

Flavonoids exclusively present in mycorrhizal roots of white clover exhibit a different effect on arbuscular mycorrhizal fungi than flavonoids exclusively present in non-mycorrhizal roots of white clover

Abstract The flavonoids 5,6,7,8,9-hydroxy chalcone, 3,7-hydroxy-4′methoxy flavone, 5,6,7,8-hydroxy-4′-methoxy flavone and 3,5,6,7,4′-hydroxy flavone can be detected only in non-mycorrhizal roots of white clover, but not in mycorrhizal roots, whereas the flavonoids acacetin, quercetin and rhamnetin are only present in mycorrhizal roots. We tested the effect of several concentrations of these compounds on spore germination, hyphal growth, hyphal branching, formation of clusters of auxiliary cells and of secondary spores of the arbuscular mycorrhizal fungi Gigaspora rosea, Gigaspora margarita, Glomus mosseae and Glomus intraradices. Our results indicate that depending on the flavonoid, the tested compounds are involved at different stages in the regulation of mycorrhization. This hypothesis is strengthened by their differing effect on several AM fungal growth parameters. Furthermore, our study provides more data on the AM fungus genus/species specificity of flavonoids.

A new look into the reaction between ergosterol and singlet oxygen in vitro

The reaction of ergosterol (ERGO) with singlet oxygen in vitro was studied by using different combinations of the photosensitizers (i.e. rose Bengal and eosine) and solvents (i.e. pyridine, ethanol and methyl tert-butyl ether) and all the products obtained were isolated and fully characterized (mp, Rf, UV, 1H-NMR, 13C-NMR, EI-MS, ESI-MS and HR-MS). In pyridine. together with the expected (22E)-5alpha,8alpha-epidioxyergosta-6,22-dien-3beta-ol, EEP, the keto derivative (22E)-3beta-hydroxyergosta-5,8(9),22-trien-7-one. KE, was obtained. In ethanol the expected EEP was obtained together with (22E)-5alpha,8alpha-epidioxyergosta-6,9,22-trien-3beta-ol, EEP9(11), and (22E)-ergosta-6,9,22-triene-3beta,5alpha,8alpha-triol, DHOE, as main products and (22E)-ergosta-5,7,9,22-tetraen-3beta-ol, DHE, in trace amounts In methyl tert-butyl ether, a complex mixture of EEP, KE, DHOE, EEP9(11), DHE, together with (22E)-7alpha-hydroperoxyergosta-5.8(9),22-trien-3beta-ol, EHP, and (22E)-ergosta-5,8(9),22-triene-3beta, 7alpha-diol, EH, was obtained. The minor products were characterized and showed strong dependence on the reaction medium. The regioselective and stereoselective character of the singlet oxygen attack on the ERGO diene moiety is discussed in terms of ERGO HOMOs properties.

Antiviral activity of natural and synthetic β-carbolines against dengue virus.

Dengue virus (DENV) is the most prevalent mosquito borne viral pathogen worldwide. In this work we first evaluated the antiviral activity of natural and synthetic β-carbolines against DENV-2 multiplication in cell cultures. We determined that the natural β-carboline harmol and a synthetic harmine derivative, 9N-methylharmine, exhibit inhibitory effect on DENV-2 production without virucidal activity. The active compounds were inhibitory of all DENV serotypes, being DENV-2 the more susceptible to their antiviral action. The mode of action of 9N-methylharmine against DENV-2 was further explored. We determined that the derivative neither affects viral adsorption-internalization events nor viral RNA synthesis. The quantification of intracellular and extracellular viral genomes and infectious virus particles indicated that 9N-methylharmine would impair the maturation and release of virus particles to the extracellular medium affecting the spreading of the infection. Furthermore, we also determined that 9N-methylharmine antiviral activity is not related to the ability of the compound to downregulate p38 MAPK phosphorylation.

The photophysics of nitrocarbazoles studied by using spectroscopic, photoacoustic and luminescence techniques

The photophysical behaviour of 1-nitrocarbazol and 3-nitrocarbazol in different organic solvents has been studied by using spectroscopic, luminescence and photoacoustic techniques. Absorption spectra and triplet state transient spectra were recorded and formation quantum yields and lifetimes determined. Phosphorescence emission at 77 K and laser induced luminescence in acetonitrile solution at 298 K for the nitrocarbazoles were studied. Results are discussed in terms of the optimized structure of 1-nitrocarbazole and 3-nitrocarbazole and compared with that of carbazole. The nitro group attached to the carbazole moiety induces important changes in the photophysical behavior of those compounds.

Singlet-oxygen ene reaction with 3β-substituted stigmastanes. An alternative pathway for the classical Schenck rearrangement

The course of the singlet-oxygen ene reaction with stigmasta-5,22-dienes may be controlled if in the substrate a good leaving group as substituent is present at 3-C. Thus when the 5α-hydroperoxystigmasta-5,22-diene is formed instead of the well known allylic rearrangement to yield the 7α-hydroperoxystigmasta-5,22-diene isomer an intramolecular nucleophilic substitution can then occur yielding 5α-hydroxystigmasta-6,22-dien-3-one. Various stigmasta-5,22-dienes were chosen to elucidate which feature of the stigmastane is necessary to control the course of the reaction. Thus, 3β-F, 3β-Cl, 3β-Br, 3β-I and 3α-Br-stigmasta-5,22-dienes were firstly prepared and fully characterized in order to study their reaction with 1O2 under different experimental conditions. 3β-Acetoxy- and 3β-mesyloxy-stigmasta-5,22-diene derivatives were also prepared and studied.