Phylogenetic isolation of host trees affects assembly of local Heteroptera communities.

A host may be physically isolated in space and then may correspond to a geographical island, but it may also be separated from its local neighbours by hundreds of millions of years of evolutionary history, and may form in this case an evolutionarily distinct island. We test how this affects the assembly processes of the host's colonizers, this question being until now only invoked at the scale of physically distinct islands or patches. We studied the assembly of true bugs in crowns of oaks surrounded by phylogenetically more or less closely related trees. Despite the short distances (less than 150 m) between phylogenetically isolated and non-isolated trees, we found major differences between their Heteroptera faunas. We show that phylogenetically isolated trees support smaller numbers and fewer species of Heteroptera, an increasing proportion of phytophages and a decreasing proportion of omnivores, and proportionally more non-host-specialists. These differences were not due to changes in the nutritional quality of the trees, i.e. species sorting, which we accounted for. Comparison with predictions from meta-community theories suggests that the assembly of local Heteroptera communities may be strongly driven by independent metapopulation processes at the level of the individual species. We conclude that the assembly of communities on hosts separated from their neighbours by long periods of evolutionary history is qualitatively and quantitatively different from that on hosts established surrounded by closely related trees. Potentially, the biotic selection pressure on a host might thus change with the evolutionary proximity of the surrounding hosts.

Role of peptide primary sequence in polyphenol-protein recognition: an example with neurotensin.

Polyphenols are known for their impact on health and one of their major properties is the formation of complexes with proteins. To investigate the involvement of polyphenol-protein complexes in health, the interactions between bioactive polyphenols and neurotensin were examined by structural NMR and molecular modeling. Neurotensin is a linear bioactive tridecapeptide and polyphenols seem to affect the NT metabolism. We studied the polyphenols resveratrol and its glucoside the piceid in order to observe the possible role of glucose group and the penta-O-galloyl-D-glucopyranose (PGG). NMR data and molecular modeling showed that interaction occurred with the three polyphenols involving hydrophobic stacking and hydrogen bonds. Moreover, the peptide primary sequence plays a role in the specificity of complex formation.

Polyphenols newly extracted in red wine from southwestern France by centrifugal partition chromatography.

Polyphenols from the ethyl acetate extracts of red wine were successfully fractionated using a four-step process (solvent extraction, ion-exchange column chromatography, centrifugal partition chromatography, and semipreparative HPLC), which resulted in the isolation of 22 compounds belonging to different classes of polyphenols (stilbenes, cinnamic acids, flavonoids). Five of them are red wine constituents reported for the first time. The newly isolated compounds include resveratrol dimers, dihydroflavonols, and a cinnamic derivative.

Sugar sensing and Ca2+-calmodulin requirement in Vitis vinifera cells producing anthocyanins.

We have previously reported that sucrose modulates anthocyanin biosynthesis in cell suspension cultures of Vitis vinifera L. The main role of sugar in this response does not seem to be that of general carbohydrate source for the supply of energy. In the present work, a number of pharmacological agents were used to further investigate the components of the signal transduction pathway involved in the induction of anthocyanin biosynthesis by sugar. We found that the phosphorylation of hexose by hexokinase, but not its transport, has to be taken into account for the sucrose signal transduction leading to anthocyanin accumulation. Indeed, 3-O-methylglucose, a glucose analog transported into cells but not phosphorylated by hexokinase, has no effect on anthocyanin production. Mannose mimics the effect of sucrose in grape cells, and mannoheptulose, a specific inhibitor of hexokinase, reduces the accumulation of anthocyanins in response to sucrose. The results with the two latter analogs are discussed. Ca2+ channel blockers, verapamil and LaCl3, which were used to investigate the role of extracellular Ca2+, all inhibited the sugar response. Ca2+ depletion by pretreatment with ethylene glycol bis (beta-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA) also blocked the sugar response, which was partially recovered when Ca2+ was added exogenously after Ca2+ depletion. The use of two potent calmodulin antagonists, N-(6-aminohexyl)-5-chloro-1-naphtalenesulphonamide (W7) and chlorpromazine, showed that calmodulin is involved in the sugar signal transduction. A protein kinase inhibitor, 6-dimethylaminopurine (6-DMAP), and the protein phosphatase inhibitors, endothall and cantharidin, also inhibited the sugar response. The results of the present study suggest the involvement of several components of general signal transduction pathways such as Ca2+, calmodulin, and protein kinases phosphatases in the induction of anthocyanin biosynthesis by sugar.