Membrane microheterogeneity: Förster resonance energy transfer characterization of lateral membrane domains

Lateral membrane heterogeneity, in the form of lipid rafts and microdomains, is currently implicated in cell processes including signal transduction, endocytosis, and cholesterol trafficking. Various biophysical techniques have been used to detect and characterize lateral membrane domains. Among these, Förster resonance energy transfer (FRET) has the crucial advantage of being sensitive to domain sizes smaller than 50-100 nm, below the resolution of optical microscopy but, apparently, similar to those of rafts in cell membranes. In the last decade, several formalisms for the analysis of FRET in heterogeneous membrane systems have been derived and applied to the study of microdomains. They are critically described and illustrated here.     

Somatostatin binding sites in cytosolic fractions of parietal and non-parietal cells from rabbit fundic mucosa

Specific binding sites for somatostatin have been found in the cytosolic fractions of both parietal and non-parietal cells from rabbit gastric fundic mucosa. The stoichiometric data suggested the presence of two classes of binding sites in both types of ceils. The number of low-affinity binding sites was significantly higher in parietal cells than in non-parietal cells. The reverse was true for the high-affinity binding sites. However, the affinity of each class of binding sites was similar in the cytosolic fractions of both parietal and non-parietal ceils. It thus appears that low-affinity somatostatin binding sites are mainly located in the parietal ceils whereas the high-affinity sites occur principally in the non-parietal cells.     

Rapid Quantification of Phototrophic Microorganisms and their Physiological State through their Colour

Quantification of phototrophic organisms on solid substrata together with their metabolic activity can be assessed easily, reliably and quickly through measurement of the organisms' colour. For that purpose only a chroma meter for solid substrata able to quantify the three components of colour is needed. A correlation between these three components and the number of organisms and their physiological state was demonstrated. The methodology developed here makes it possible to save time and materials in comparison with traditional microbiological methods. Moreover, it is a non-destructive method which can be used directly on site and in site. This characteristic is important when microbial environmental monitoring of cultural heritage is involved.     

Somatostatin action on insulin secretion induced by chicken and porcine vasoactive intestinal peptide in the perfused rat pancreas

The isolated perfused rat pancreas with duodenal exclusion was used to study the stimulation of glucose-induced insulin release in response to chicken and porcine vasoactive intestinal peptide (VIP). The insulin response to 5.5 or 16.7 mM glucose was markedly enhanced by 750 pM porcine VIP and a concentration of 250 pM was still effective. At 250 pM, chicken VIp exhibited a slightly higher potency than porcine VIP at both glucose concentrations. The main difference between the two peptides was that the effect of porcine VIP disappeared immediately after the peptide suppression but tha of chicken VIP persisted for an additional period of 8-10 min. Somatostatin (10 ng/ml) blocked the stimulatory effect of both VIP molecules on glucose-induced insulin secretion. After suppression of VIP and somatostatin from the perfusion medium, insulin release increased to levels higher than those with glucose alone in the case of the avian peptide, but not in that porcine VIP. The data are consistent with previous results in the literature on stimulation of exocrine pancreas secretion and interaction with intestinal epithelium.     

Efficient colonization of the endophytes Herbaspirillum huttiense RCA24 and Enterobacter cloacae RCA25 influences the physiological parameters of Oryza sativa L. cv. Baldo rice

Several important bacterial characteristics, such as biological nitrogen fixation, phosphate solubilization, 1-aminocyclopropane-1-carboxylate deaminase activity and production of siderophores and phytohormones, can be assessed as plant growth promotion traits. Our aim was to evaluate the effects of nitrogen fixing and indole-3-acetic acid (IAA) producing endophytes in two Oryza sativa cultivars (Baldo and Vialone Nano). Three bacteria, Herbaspirillum huttiense RCA24, Enterobacter asburiae RCA23 and Staphylococcus sp. 377, producing different IAA levels, were tested for their ability to enhance nifH gene expression and nitrogenase activity in Enterobacter cloacae RCA25. Results showed that H. huttiense RCA24 performed best. Improvement in nitrogen fixation and changes in physiological parameters such as chlorophyll, nitrogen content and shoot dry weight were observed for plants co-inoculated with strains RCA25 and RCA24 in a 10:1 ratio. Based on confocal laser scanning microscopy analysis, strain RCA24 was the best colonizer of the root interior and the only IAA producer located in the same root niche occupied by RCA25 cells. This work shows that the choice of a bio-inoculum having the right composition is one of the key aspects to be considered for the inoculation of a specific host plant cultivar with microbial consortia.     

Feeding behavior,life history,and virus transmission ability of Bemisia tabaci Mediterranean species (Hemiptera: Aleyrodidae) under elevated CO2

The continuous rise of CO₂ concentrations in the atmosphere is reducing plant nutritional quality for herbivores and indirectly affects their performance. The whitefly (Bemisia tabaci, Gennadius) is a major worldwide pest of agricultural crops causing significant yield losses. This study investigated the plant‐mediated indirect effects of elevated CO₂ on the feeding behavior and life history of B. tabaci Mediterranean species. Eggplants were grown under elevated and ambient CO₂ concentrations for 3 weeks after which plants were either used to monitor the feeding behavior of whiteflies using the Electrical Penetration Graph technique or to examine fecundity and fertility of whiteflies. Plant leaf carbon, nitrogen, phenols and protein contents were also analyzed for each treatment. Bemisia tabaci feeding on plants exposed to elevated CO₂ showed a longer phloem ingestion and greater fertility compared to those exposed to ambient CO₂ suggesting that B. tabaci is capable of compensating for the plant nutritional deficit. Additionally, this study looked at the transmission of the virus Tomato yellow leaf curl virus (Begomovirus) by B. tabaci exposing source and receptor tomato plants to ambient or elevated CO₂ levels before or after virus transmission tests. Results indicate that B. tabaci transmitted the virus at the same rate independent of the CO₂ levels and plant treatment. Therefore, we conclude that B. tabaci Mediterranean species prevails over the difficulties that changes in CO₂ concentrations may cause and it is predicted that under future climate change conditions, B. tabaci would continue to be considered a serious threat for agriculture worldwide.