Responses of Two Olive Tree (Olea Europaea L.) Cultivars to Elevated CO2 Concentration in the Field

Five-year-old plants of two olive cultivars (Frantoio and Moraiolo) grown in large pots were exposed for 7 to 8 months to ambient (AC) or elevated (EC) CO₂ concentration in a free-air CO₂ enrichment (FACE) facility. Exposure to EC enhanced net photosynthetic rate (P _N) and decreased stomatal conductance, leading to greater instantaneous transpiration efficiency. Stomata density also decreased under EC, while the ratio of intercellular (C _i) to atmospheric CO₂ concentration and chlorophyll content did not differ, except for the cv. Moraiolo after seven months of exposure to EC. Analysis of the relationship between photosynthesis and C _i indicated no significant change in carboxylation efficiency of ribulose-1,5-bisphosphate carboxylase/oxygenase after five months of exposure to EC. Based on estimates derived from the P _N-C _i relationship, there were no apparent treatment differences in daytime respiration, CO₂ compensation concentration, CO₂-saturated photosynthetic rate, or photosynthetic rate at the mean C _i, but there was a reduction in stomata limitation to P _N at EC. Thus 5-year-old olive trees did not exhibit down regulation of leaf-level photosynthesis in their response to EC, though some indication of adjustment was evident for the cv. Frantoio with respect to the cv. Moraiolo.     

The ORC/Cdc6/MCM2-7 complex facilitates MCM2-7 dimerization during prereplicative complex formation

The replicative mini-chromosome-maintenance 2–7 (MCM2-7) helicase is loaded in Saccharomyces cerevisiae and other eukaryotes as a head-to-head double-hexamer around origin DNA. At first, ORC/Cdc6 recruits with the help of Cdt1 a single MCM2-7 hexamer to form an ‘initial’ ORC/Cdc6/Cdt1/MCM2-7 complex. Then, on ATP hydrolysis and Cdt1 release, the ‘initial’ complex is transformed into an ORC/Cdc6/MCM2-7 (OCM) complex. However, it remains unclear how the OCM is subsequently converted into a MCM2-7 double-hexamer. Through analysis of MCM2-7 hexamer-interface mutants we discovered a complex competent for MCM2-7 dimerization. We demonstrate that these MCM2-7 mutants arrest during prereplicative complex (pre-RC) assembly after OCM formation, but before MCM2-7 double-hexamer assembly. Remarkably, only the OCM complex, but not the ‘initial’ ORC/Cdc6/Cdt1/MCM2-7 complex, is competent for MCM2-7 dimerization. The MCM2-7 dimer, in contrast to the MCM2-7 double-hexamer, interacts with ORC/Cdc6 and is salt-sensitive, classifying the arrested complex as a helicase-loading intermediate. Accordingly, we found that overexpression of the mutants cause cell-cycle arrest and dominant lethality. Our work identifies the OCM complex as competent for MCM2-7 dimerization, reveals MCM2-7 dimerization as a limiting step during pre-RC formation and defines critical mechanisms that explain how origins are licensed.     

Silver enhancement of protein A-gold probes on resin-embedded ultrathin sections

Summary A simple method is described allowing the enhancement of the visibility of small gold probes for the electron microscopy.This method, which allows the silver intensification of gold directly on epon-embedded ultrathin sections, was used for the electron microscopic localization of Mouse Mammary Tumor Virus (MMTV) antigens in cultured cells derived from GR and BALB/cfRIII mouse mammary tumors. After the immunostaining with the preembedding protein A-gold technique, the ultrathin sections, placed on 200 mesh copper grids, were rehydrated and exposed to a photographic developer containing silver nitrate. During this physical development gold particles are incapsulated in growing shells of metallic silver, which gradually become more and more visible. We were able to obtain a heavy labelling of the viral particles, well visible even at low magmfication, with a negligeable background staining.The present technique can be useful whenever it is necessary to use the smallest gold probes today available.Supported by contract No. 85.02038.44 from the National Research Council, Rome, Progetto Finalizzato Oncologia     

Ethylene dimerization catalyzed by mixed phosphine–iminophosphorane nickel(II) complexes: a DFT investigation

A computational study utilizing density functional theory (DFT) was performed to analyze the mechanism of ethylene dimerization catalyzed by (P,N) nickel(II) complexes, where (P,N) is a mixed phosphine–iminophosphorane ligand. Two plausible reaction pathways were considered, namely the Cossee and metallacycle pathways, for three model systems. The fundamental role of ligand assymetry and the importance of steric and trans effects were elucidated. In order to discriminate between both mechanisms, the activation of the precatalyst by trimethylaluminum was modeled. The results obtained allow the establishment of useful guidelines for creating new specifically tailored nickel-based catalysts for controlled dimerization.     

Line field confocal optical coherence tomography: An adjunctive tool in the diagnosis of autoimmune bullous diseases

Autoimmune bullous diseases (AIBDs) still represent a considerable a source of morbidity and mortality: early identification of a specific AIBD is often difficult due to overlapping clinical and/or laboratory features and time-consuming invasive laboratory tests. We aimed to investigate the potential role of a new imaging technology, line-field confocal optical coherence tomography (LC-OCT), in the non-invasive diagnosis of AIBDs. LC-OCT was performed at lesional, perilesional and contralateral healthy sites in 30 patients, before histology and direct immunofluorescence. LC-OCT examination was able to identify the level of split (subcorneal/suprabasal/subepidermal/sublamina densa), to provide detailed images of the bulla roof morphology and content (eg, erythrocytes/acantholytic cells/polymorphonucleates). Areas of intra/subepidermal detachment were also detected also at clinically normal perilesional skin sites. LC-OCT can support physicians, real time and at bed-site, in the differential diagnosis of various AIBDs and their mimickers. Moreover, it can be used for the identification of subclinical lesions and therapy tapering.     

Sucrose signaling in plants: A world yet to be explored

The role of sucrose as a signaling molecule in plants was originally proposed several decades ago. However, recognition of sucrose as a true signal has been largely debated and only recently this role has been fully accepted. The best-studied cases of sucrose signaling involve metabolic processes, such as the induction of fructan or anthocyanin synthesis, but a large volume of scattered information suggests that sucrose signals may control a vast array of developmental processes along the whole life cycle of the plant. Also, wide gaps exist in our current understanding of the intracellular steps that mediate sucrose action. Sucrose concentration in plant tissues tends to be directly related to light intensity, and inversely related to temperature, and accordingly, exogenous sucrose supply often mimics the effect of high light and cold. However, many exceptions to this rule seem to occur due to interactions with other signaling pathways. In conclusion, the sucrose role as a signal molecule in plants is starting to be unveiled and much research is still needed to have a complete map of its significance in plant function.     

A DFT study of the Al2Cl6-catalyzed Friedel–Crafts acylation of phenyl aromatic compounds

The reaction pathways of several Friedel–Crafts acylations involving phenyl aromatic compounds were studied using density functional theory. The reactions were related to the Friedel–Crafts polycondensation of polyaryletherketones. In particular, the acylation of benzene with benzoyl chloride to form benzophenone and variations on this reaction were investigated. The acylation of benzene by one molecule of terephthaloyl chloride or isophthaloyl chloride as well as acylations at the m-, o-, and p-positions of diphenyl ether with one molecule of benzoyl chloride were studied. Adding an additional acyl chloride group to the electrophile appeared to have little influence on the reaction pathway, although the activation energy for the C–C bond-forming steps that occurred when isophthaloyl choride was used was different to the activation energy observed when terephthaloyl chloride was used. Upon changing the nucleophile to diphenyl ether, the reactivity changed according to the trend predicted on based on the o-, p-directing effects of the ether group. The deprotonation step that restored aromaticity varied widely according to the reaction. The rate-determining step in all of the studied reactions was the formation of the acylium ion, followed in importance by either the formation of the Wheland intermediate or the abstraction of hydrogen, depending on the reactivity of the nucleophile.