The only African wild tobacco, Nicotiana africana: Alkaloid content and the effect of herbivory

Herbivory in some Nicotiana species is known to induce alkaloid production. This study examined herbivore-induced defenses in the nornicotine-rich African tobacco N. africana, the only Nicotiana species indigenous to Africa. We tested the predictions that: 1) N. africana will have high constitutive levels of leaf, flower and nectar alkaloids; 2) leaf herbivory by the African bollworm Helicoverpa armigera will induce increased alkaloid levels in leaves, flowers and nectar; and 3) increased alkaloid concentrations in herbivore-damaged plants will negatively affect larval growth. We grew N. africana in large pots in a greenhouse and exposed flowering plants to densities of one, three and six fourth-instar larvae of H. armigera, for four days. Leaves, flowers and nectar were analyzed for nicotine, nornicotine and anabasine. The principal leaf alkaloid was nornicotine (mean: 28 µg/g dry mass) followed by anabasine (4.9 µg/g) and nicotine (0.6 µg/g). Nornicotine was found in low quantities in the flowers, but no nicotine or anabasine were recorded. The nectar contained none of the alkaloids measured. Larval growth was reduced when leaves of flowering plants were exposed to six larvae. As predicted by the optimal defense theory, herbivory had a localized effect and caused an increase in nornicotine concentrations in both undamaged top leaves of herbivore damaged plants and herbivore damaged leaves exposed to one and three larvae. The nicotine concentration increased in damaged compared to undamaged middle leaves. The nornicotine concentration was lower in damaged leaves of plants exposed to six compared to three larvae, suggesting that N. africana rather invests in new growth as opposed to protecting older leaves under severe attack. The results indicate that the nornicotine-rich N. africana will be unattractive to herbivores and more so when damaged, but that potential pollinators will be unaffected because the nectar remains alkaloid-free even after herbivory

Branched versus linear alkane adsorption in carbonaceous slit pores

The presence of carbonaceous deposits on the internal surfaces of a spark ignition engine has been linked in the literature to impaired vehicle performance, as manifested by increased knocking, higher fuel consumption, higher emissions and other adverse effects. One of the proposed mechanisms, in which the deposits affect the processes in the engine, is the adsorption and desorption of fuel components in the pores within the deposit. In this article we investigate this mechanism in more detail by considering single component adsorption of normal and branched alkanes in selected model slit pores representing the structure of the deposits. We further extend these studies to the binary mixture of normal heptane and isooctane, corresponding to a primary reference fuel blend. In particular, we show that in larger pores adsorption selectivity towards isooctane is about 1.2 on average throughout the pressure range. However, in the smaller 10 Å pore selectivity towards isooctane can be in excess of three as a result of packing effects. These results are then placed in the context of engine performance issues

Comparative Genomic Analysis of Drosophila melanogaster and Vector Mosquito Developmental Genes

Genome sequencing projects have presented the opportunity for analysis of developmental genes in three vector mosquito species: Aedes aegypti, Culex quinquefasciatus, and Anopheles gambiae. A comparative genomic analysis of developmental genes in Drosophila melanogaster and these three important vectors of human disease was performed in this investigation. While the study was comprehensive, special emphasis centered on genes that 1) are components of developmental signaling pathways, 2) regulate fundamental developmental processes, 3) are critical for the development of tissues of vector importance, 4) function in developmental processes known to have diverged within insects, and 5) encode microRNAs (miRNAs) that regulate developmental transcripts in Drosophila. While most fruit fly developmental genes are conserved in the three vector mosquito species, several genes known to be critical for Drosophila development were not identified in one or more mosquito genomes. In other cases, mosquito lineage-specific gene gains with respect to D. melanogaster were noted. Sequence analyses also revealed that numerous repetitive sequences are a common structural feature of Drosophila and mosquito developmental genes. Finally, analysis of predicted miRNA binding sites in fruit fly and mosquito developmental genes suggests that the repertoire of developmental genes targeted by miRNAs is species-specific. The results of this study provide insight into the evolution of developmental genes and processes in dipterans and other arthropods, serve as a resource for those pursuing analysis of mosquito development, and will promote the design and refinement of functional analysis experiments

Tight junctions: from simple barriers to multifunctional molecular gates

Epithelia and endothelia separate different tissue compartments and protect multicellular organisms from the outside world. This requires the formation of tight junctions, selective gates that control paracellular diffusion of ions and solutes. Tight junctions also form the border between the apical and basolateral plasma-membrane domains and are linked to the machinery that controls apicobasal polarization. Additionally, signalling networks that guide diverse cell behaviours and functions are connected to tight junctions, transmitting information to and from the cytoskeleton, nucleus and different cell adhesion complexes. Recent advances have broadened our understanding of the molecular architecture and cellular functions of tight junctions

Isolation and Identification of the Wax Esters from the Cuticular Waxes of Green Tobacco Leaf

Abstract Recent studies in our laboratory on the cuticular chemicals of green tobacco leaf have revealed the presence of wax esters, composed of fatty acids bound to fatty alcohols. Cuticular components of young green NC 2326 tobacco leaves were removed with methylene chloride, and partitioned between hexane and 80 % MeOH-H2O. The hexane-soluble fraction, which contained wax esters, paraffinic hydrocarbons, and fatty alcohols, was separated by silicic acid column chromatography, and the resulting wax ester fraction was further purified by lipophilic gel chromatography. Initial analyses of the wax ester fraction by capillary gas chromatography [GC] and capillary GC / MS, on a short fused silica [FS] SE-54 capillary column, indicated the presence of C30 - C52 wax esters. Application of the cold on-column injection technique and use of immobilized stationary phase, FS SE-54 capillary columns greatly improved the GC separation of the complex wax ester fraction and permitted the identification of individual wax ester isomers. Identification of wax ester isomers by GC/MS relied upon the presence of a molecular ion and ions characteristic of the acid and alcohol moieties. For the acid portion, these ions included the acid MW + 1 a.m.u. and MW - 17 a.m.u. ions, while for the alcohol, they were the alcohol MW - 18 a.m.u. and MW + 27 a.m.u. ions. Saponification of the wax ester fraction and subsequent analyses of the alcohols (as trimethylsilyl ethers) and acids (as methyl esters) revealed extensive iso- and anteiso-methyl branching of the acid moieties. The wax ester isomers with iso- and anteiso- methyl-branched acid moieties were separated from each other and from the normal straight-chain isomers by capillary GC and were identified by GC/MS, based upon characteristic ions resulting from the losses of the iso-branched (MW - 43 a.m.u.) and anteiso-branched (MW - 57 a.m.u.) groups from the molecular ion and from the acid moiety. One hundred and seventy individual wax esters were identified.</jats:p

The Contribution of Sucrose Esters to Tobacco Smoke Composition

Abstract Sucrose esters, principally the 6-O-acetyl-2,3,4-tri-O-(3-methylvaleryl)-a-D-glucopyranosyl-b-D-fructofuran-oside isomer, isolated from the cuticular waxes of green T.I. 165 tobacco leaf, were evaluated as enhancers of 3-methylvaleric acid in the smoke of a tobacco deficient in this important flavor compound. Analyses of the products from semi-micro pyrolyses of sucrose and isolated sucrose esters, over a temperature range of 250°C - 850°C, showed that free sucrose produced 5-hydroxy-methylfurfural as the major component, whereas the ester isolate yielded 3-methylvaleric acid and lesser amounts of isomeric C4 and C5 aliphatic acids. Incorporation of sucrose ester isolate of T.I. 165 leaf into cigarettes prepared from flue-cured NC 2326 tobacco, the smoke of which is essentially devoid of 3-methylvaleric acid, resulted in a total particulate matter with enhanced levels of this compound. The data indicated that addition of approximately 2 mg of sucrose ester isolate per cigarette produced levels of 3-methylvaleric acid in the smoke of NC 2326 cigarettes that were comparable to levels observed in the smoke from cigarettes containing all T.I. 165 or blended Turkish tobacco.</jats:p

Defining Participant Exposure Measures in Web-Based Health Behavior Change Programs

BACKGROUND: Published research on the use of Web-based behavior change programs is growing rapidly. One of the observations characterized as problematic in these studies is that participants often make relatively few website visits and spend only a brief time accessing the program. Properly structured websites permit the unobtrusive measurement of the ways in which participants access (are exposed to) program content. Research on participant exposure to Web-based programs is not merely of interest to technologists, but represents an important opportunity to better understand the broader theme of program engagement and to guide the development of more effective interventions. OBJECTIVES: The current paper seeks to provide working definitions and describe initial patterns of various measures of participant exposure to ChewFree.com, a large randomized controlled trial of a Web-based program for smokeless tobacco cessation. METHODS: We examined measures of participant exposure to either an Enhanced condition Web-based program (interactive, tailored, and rich-media program) or a Basic condition control website (static, text-based material). Specific measures focused on email prompting, participant visits (number, duration, and pattern of use over time), and Web page viewing (number of views, types of pages viewed, and Web forum postings). RESULTS: Participants in the ChewFree.com Enhanced condition made more visits and spent more time accessing their assigned website than did participants assigned to the Basic condition website. In addition, exposure data demonstrated that Basic condition users thoroughly accessed program content, indicating that the condition provided a meaningful, face-valid control to the Enhanced condition. CONCLUSIONS: We recommend that researchers conducting evaluations of Web-based interventions consider the collection and analysis of exposure measures in the broader context of program engagement in order to assess whether participants obtain sufficient exposure to relevant program content