γ‐Unsaturated Aldehydes as Potential Lilial Replacers

A series of Claisen rearrangements was undertaken in order to find a replacement for Lilial (=3‐(4‐(tert‐butyl)phenyl)‐2‐methylpropanal), a high‐tonnage perfumery ingredient with a lily‐of‐the‐valley odour, which is a CMR2 material [1]. 5,7,7‐Trimethyl‐4‐methyleneoctanal ( 10 ), the synthesis of which is described, became the main lead. It possesses an odour which is very close to that of Lilial but lacks its substantivity. Aldehydes with higher molecular weights than that of 10 were, therefore, synthesised in order to boost substantivity and to understand the structural requirements for a ‘Lilial’ odour. The aldehydes were obtained via Claisen rearrangements of ‘exo‐methylidene’ vinyl ethers, allenyl vinyl ethers, or allenyl allyl ethers. Alternatively, coupling of terminal alkynes with allyl alcohols led to the desired aldehydes. Derivatives of 10 and their sila analogues were also synthesised. The olfactory properties of all synthesised molecules were evaluated for possible structure? odour relationships (SOR).     

The signaling role of extracellular ATP and its dependence on Ca2+ flux in elicitation of Salvia miltiorrhiza hairy root cultures

The application of a polysaccharide elicitor from yeast extract,YE, to Salvia miltiorrhiza hairy root cultures induced transientrelease of ATP from the roots to the medium, leading to a dose-dependentincrease in the extracellular ATP (eATP) level. The eATP levelrose to a peak (about 6.5 nM with 100 mg l^–1 YE) at about10 h after YE treatment, but dropped to the control level 6h later. The elicitor-induced ATP release was dependent on membraneCa²⁺ influx, and abolished by the Ca²⁺ chelator EGTA or thechannel blocker La³⁺. The YE-induced H₂O₂ production was stronglyinhibited by reactive blue (RB), a specific inhibitor of membranepurinoceptors. On the other hand, the application of exogenousATP at 10–100 µM to the cultures also induced rapidand dose-dependent increases in H₂O₂ production and medium pH,both of which were effectively blocked by RB and EGTA. The non-hydrolyzableATP analog ATPS was as effective as ATP, but the hydrolyzedderivatives ADP or AMP were not so effective in inducing thepH and H₂O₂ increases. Our results suggest that ATP releaseis an early event and that eATP plays a signaling role in theelicitation of plant cell responses; Ca²⁺ is required for activationof the elicitor-induced ATP release and the eATP signal transduction.This is the first report on ATP release induced by a fungalelicitor and its involvement in the elicitor-induced responsesin plant cells.     

Distribution of the stimulatory GTP-binding proteins, Gs and Golf, within olfactory neuroepithelium

Several lines of evidence suggest that, for certain odorants,olfactory signal transduction may be mediated by a stimulatoryG-protein coupled adenylate cyclase cascade. Two stimulatoryG-proteins, G_olf and G_s, are expressed in olfactory tissue.To evaluate their relative contributions to the process of odorantsignal transduction, specific antisera were used to determinethe distribution and relative abundance of G_olf and G_s in ratolfactory neuroepithelium and olfactory sensory cilia. Theseanalyses demonstrate that (1) Golf is far more abundant thanG_s in olfactory neuroepithelium and (2) G_olf is essentiallythe only stimulatory G-protein present in olfactory sensorycilia. ¹Present address: Gene Expression Laboratory, The Salk Institute,PO Box 85800, San Diego, CA 92138, USA     

From pull-down data to protein interaction networks and complexes with biological relevance

Motivation: Recent improvements in high-throughput Mass Spectrometry(MS) technology have expedited genome-wide discovery of protein–proteininteractions by providing a capability of detecting proteincomplexes in a physiological setting. Computational inferenceof protein interaction networks and protein complexes from MSdata are challenging. Advances are required in developing robustand seamlessly integrated procedures for assessment of protein–proteininteraction affinities, mathematical representation of proteininteraction networks, discovery of protein complexes and evaluationof their biological relevance. Results: A multi-step but easy-to-follow framework for identifyingprotein complexes from MS pull-down data is introduced. It assessesinteraction affinity between two proteins based on similarityof their co-purification patterns derived from MS data. It constructsa protein interaction network by adopting a knowledge-guidedthreshold selection method. Based on the network, it identifiesprotein complexes and infers their core components using a graph-theoreticalapproach. It deploys a statistical evaluation procedure to assessbiological relevance of each found complex. On Saccharomycescerevisiae pull-down data, the framework outperformed othermore complicated schemes by at least 10% in F₁-measure and identified610 protein complexes with high-functional homogeneity basedon the enrichment in Gene Ontology (GO) annotation. Manual examinationof the complexes brought forward the hypotheses on cause offalse identifications. Namely, co-purification of differentprotein complexes as mediated by a common non-protein molecule,such as DNA, might be a source of false positives. Protein identificationbias in pull-down technology, such as the hydrophilic bias couldresult in false negatives. Contact: samatovan{at}ornl.gov Supplementary information: Supplementary data are availableat Bioinformatics online. Associate Editor: Jonathan Wren Present address: Department of Biomedical Informatics, VanderbiltUniversity, Nashville, TN 37232. The authors wish it to be known that, in their opinion, thefirst two authors should be regarded as joint First Authors.     

Background odour induces adaptation and sensitization of olfactory receptors in the antennae of houseflies

The presence of background odour was found to have a small but significant effect on the sensitivity of the antennal olfactory system of houseflies, Musca domestica Linnaeus (Diptera: Muscidae), to new pulses of odour. We show that cross-adaptation and cross-sensitization between a background odour of (+/-)-1-octen-3-ol and pulses of (+/-)-1-octen-3-ol, 2-pentanone and R-(+)-limonene can occur, confirming that olfactory receptor cells are sensitive to different odours. Background odour can increase the responses to low concentration odour pulses and decrease the responses to higher concentration odour pulses. It is suggested that background odour has a larger effect on olfactory receptor cells that respond with a tonic increase of spike frequency, giving information about the level of odour concentration, i.e. the 'static' environment. Cells that respond in a phasic way only provide information on the dynamics of the olfactory environment.     

Mining SARS-CoV protease cleavage data using non-orthogonal decision trees: a novel method for decisive template selection

Motivation: Although the outbreak of the severe acute respiratorysyndrome (SARS) is currently over, it is expected that it willreturn to attack human beings. A critical challenge to scientistsfrom various disciplines worldwide is to study the specificityof cleavage activity of SARS-related coronavirus (SARS-CoV)and use the knowledge obtained from the study for effectiveinhibitor design to fight the disease. The most commonly usedinductive programming methods for knowledge discovery from dataassume that the elements of input patterns are orthogonal toeach other. Suppose a sub-sequence is denoted as P₂P₁P_1'P_2',the conventional inductive programming method may result ina rule like ‘if P₁ = Q, then the sub-sequence is cleaved,otherwise non-cleaved’. If the site P₁ is not orthogonalto the others (for instance, P₂, P_1' and P_2'), the predictionpower of these kind of rules may be limited. Therefore thisstudy is aimed at developing a novel method for constructingnon-orthogonal decision trees for mining protease data. Result: Eighteen sequences of coronavirus polyprotein were downloadedfrom NCBI (http://www.ncbi.nlm.nih.gov). Among these sequences,252 cleavage sites were experimentally determined. These sequenceswere scanned using a sliding window with size k to generateabout 50 000 k-mer sub-sequences (for short, k-mers). The valueof k varies from 4 to 12 with a gap of two. The bio-basis functionproposed by Thomson et al. is used to transform the k-mers toa high-dimensional numerical space on which an inductive programmingmethod is applied for the purpose of deriving a decision treefor decision-making. The process of this transform is referredto as a bio-mapping. The constructed decision trees select about10 out of 50 000 k-mers. This small set of selected k-mers isregarded as a set of decisive templates. By doing so, non-orthogonaldecision trees are constructed using the selected templatesand the prediction accuracy is significantly improved. Availability: The program for bio-mapping can be obtained byrequest to the author. Contact: z.r.yang{at}exeter.ac.uk     

Are the Tastes of Polycose and Monosodium Glutamate Unique?

To study whether Polycose and monosodium L-glutamate (L-MSG)have unique tastes differing from the traditional four basictastes, chemosensory profiles were established for Polycose,L-MSG and a group of related compounds (sucrose, maltose, monosodiumD-glutamate (D-MSG), sodium chloride, calcium chloride). Flavourswere assessed using whole-mouth tests in human subjects withnose open or clamped to reduce olfactory input. Polycose (amixture of glucose-based oligosaccharides) had a flavor consistingof an olfactory component and a maltose-like taste. L-MSG andD-MSG profiles differed from each other, and from NaCl and CaCl₂.L-MSG had a lower threshold and a higher frequency of ‘other’tastes than the D form. The data do not support a ‘polysaccharide’taste, but suggest a chiral receptor site for ‘umami’taste. Chem. Senses 21: 341–347, 1996.     

Host location and discrimination mediated through olfactory stimuli in two species of Encyrtidae

The role of olfactory stimuli in host detection and evaluation was studied in two encyrtid Hymenoptera. The first, Epidinocarsis lopezi De Santis, is a monophagous parasitoid of the cassava mealybug Phenacoccus manihoti Matile-Ferrero, itself feeding exclusively on cassava, Manihot esculenta Crantz. The second, Leptomastix dactylopii Howard, is a monophagous parasitoid of the Citrus mealybug, Planococcus citri Risso, but this latter is highly polyphagous. The behaviour of females of both parasitoids (attaction and locomotion) was compared in a tubular olfactometer for the odours of their respective hosts on cassava and poinsettia. Tests were made using: 1) healthy host-plant alone; 2) host-plant infested with unparasitized mealybugs; 3) unparasitized mealybugs only; 4) host-plant infested with parasitized mealybugs and 5) parasitized mealybugs only. Only E. lopezi was attracted by the odour of the host-plant alone, but both species were attracted by the odour of an infested host-plant and that of unparasitized mealybugs. The odour of parasitized mealybugs, alone or on host-plant, induced an undirected activity. The attraction of E. lopezi to the odour of the host-plant alone could be linked to the monophagous diet of its host, whereas the attraction of the two species of parasitoids to the odours of infested host-plants and unparasitized mealybugs could be due to the fact that both parasitoids are specialists. The behavioural response of both species to the odour of parasitized mealybugs revealed a new aspect in host discrimination: the identification of parasitized hosts could be partly mediated through olfactory stimuli, and not only through gustatory stimuli.     

Thermodynamic Roles of Solubility in Taste Responses of Amino Acids

Bitter, sour and sweet responses of amino acids were relatedto their solubilities S_w, which are virtually equal to the reciprocalsof activity coefficients at infinite dilution in water _w, andalso related to their excess partial molar entropies of transferTS_t^E. Chem. Senses 21: 405–409, 1996. Present address: 5-32-12 Tamanawa, Kamakura-shi, 247 Japan     

Peripheral Mechanisms of Pheromone Reception in Moths

Moths pheromones mostly consist of two or a few chemical componentsin a species-specific ratio. Each component is perceived bya particular type of receptor cell. Some pheromone componentscan inhibit the behavioral responses to other pheromone components.A single pheromone molecule is sufficient to elicit a nerveimpulse. The dose-response curve of single pheromone receptorneurons increases over many decades of stimulus intensity. Pheromonereceptor cells can resolve single stimulus pulses up to a frequencyof 10 pulses/s. Electrophysiological and biochemical studieson perireceptor events suggest that the pheromone moleculesinteract with the receptor cell while bound to a reduced formof the pheromone binding protein. The enzymatic degradationof pheromone found on the antennae is much too slow to accountfor the decline of the receptor potential after end of stimulation.The postulated rapid deactivation of the odor molecules adsorbedmight be performed by an oxidation of the pheromone bindingprotein. Several second messenger systems seem to be involvedin the cellular transduction mechanism (IP₃ diacylglycerol,cGMP, Ca₂₊). It is, however, not excluded that pheromone moleculescan gate single ion channels directly and thus elicit the elementaryreceptor potentials, observed at weak stimulus intensities.Chem. Senses 21: 257–268, 1996.     

A dual-respiration chamber system with automated calibration

Schoffelen, Paul F. M., Klaas R. Westerterp, Wim H. M. Saris, and Foppe Ten Hoor. A dual-respiration chambersystem with automated calibration. J. Appl.Physiol. 83(6): 2064-2072, 1997.This studycharacterizes respiration chambers with fully automated calibration.The system consists of two 14-m³pull-type chambers. Care was taken to provide a friendly environment for the subjects, with the possibility of social contact during theexperiment. Gas analysis was automated to correct for analyzer driftand barometric pressure variations and to provide ease of use. Methodsused for checking the system's performance are described. Thegas-analysis repeatability was within 0.002%. Results of alcohol combustion (50-350 ml/minCO₂) show an accuracy of 0.5 ± 2.0 (SD) % for O₂consumption and 0.3 ± 1.6% forCO₂ production for 2- to 24-hexperiments. It is concluded that response time is not the main factorwith respect to the smallest practical measurement interval (duration);volume, mixing, gas-analysis accuracy, and levels ofO₂ consumption andCO₂ production are at leastequally important. The smallest practical interval was 15-25 min,as also found with most chamber systems described in the literature. We chose to standardize 0.5 h as the minimum measurementinterval.

     

The Increase in Anchorage with Tree Size of the Tropical Tap Rooted TreeMallotus wrayi, King (Euphorbiaceae)

The mechanical development of the anchorage system of the taprooted tropical speciesMallotus wrayiKing (Euphorbiaceae) wasinvestigated by pulling over and examining trees with a diameterat breast height (d_bh) of 4.2 cm to 14.3 cm. The mode of mechanicalfailure depended upon the size of the tree: thicker trees (d_bhapprox.9 cm) failed in the ground with their tap roots pushing intothe soil on the winchward side; in smaller trees (d_bhapprox.7 cm) the trunk snapped before anchorage failure; and in verysmall trees (of d_bh<6 cm) neither type of failure occurredand the trees returned to their original upright position undamagedafter the test. The anchorage strength of the trees was correlatedwith the second power of trunk diameter rather than with thethird power that theory suggests is optimal because tap rootsdid not show an isometric increase in length or diameter. Thereforeas trees grow larger the ‘factor of safety’ againstanchorage failure falls, making them prone to fail in theirroots. These results suggest that only relatively small treespecies can rely solely on the tap root to prevent uprooting.It may be for this reason that most larger trees develop thicklateral roots.Copyright 1998 Annals of Botany Company Anchorage, tap roots, scaling,Mallotus wrayi, isometric growth, functional development, windthrow, root systems.     

Plant odour plumes as mediators of plant–insect interactions

Insect olfactory orientation along odour plumes has been studied intensively with respect to pheromonal communication, whereas little knowledge is available on how plant odour plumes (POPs) affect olfactory searching by an insect for its host plants. The primary objective of this review is to examine the role of POPs in the attraction of insects. First, we consider parameters of an odour source and the environment which determine the size, shape and structure of an odour plume, and we apply that knowledge to POPs. Second, we compare characteristics of insect pheromonal plumes and POPs. We propose a ‘POP concept’ for the olfactory orientation of insects to plants. We suggest that: (i) an insect recognises a POP by means of plant volatile components that are encountered in concentrations higher than a threshold detection limit and that occur in a qualitative and quantitative blend indicating a resource; (ii) perception of the fine structure of a POP enables an insect to distinguish a POP from an unspecific odorous background and other interfering plumes; and (iii) an insect can follow several POPs to their sources, and may leave the track of one POP and switch to another one if this conveys a signal with higher reliability or indicates a more suitable resource. The POP concept proposed here may be a useful tool for research in olfactory‐mediated plant–insect interactions.     

Olfactory learning of plant genotypes by a polyphagous insect predator

Olfactory learning may allow insects to forage optimally by more efficiently finding and using favourable food sources. Although olfactory learning has been shown in bees, insect herbivores and parasitoids, there are fewer examples from polyphagous predators. In this study, olfactory learning by a predatory coccinellid beetle is reported for the first time. In laboratory trials, adults of the aphidophagous ladybird Coccinella septempunctata did not prefer the odour of one aphid-infested barley cultivar over another. However, after feeding on aphids for 24 h on a cultivar, they preferred the odour of that particular cultivar. The mechanism appeared to be associative learning rather than sensitisation. Although inexperienced ladybirds preferred the odour of an aphid-infested barley cultivar over uninfested plants of the same cultivar, after feeding experience on a different cultivar this preference disappeared. This may indicate the acquisition and replacement of olfactory templates. The odour blends of the different aphid-infested barley cultivars varied qualitatively and quantitatively, providing a potential basis for olfactory discrimination by the ladybird. The results show that predatory coccinellids can learn to associate the odour of aphid-infested plants with the presence of prey, and that this olfactory learning ability is sensitive enough to discriminate variability between different genotypes of the same plant.     

Perceptual and neural olfactory similarity in honeybees

The question of whether or not neural activity patterns recorded in the olfactory centres of the brain correspond to olfactory perceptual measures remains unanswered. To address this question, we studied olfaction in honeybees Apis mellifera using the olfactory conditioning of the proboscis extension response. We conditioned bees to odours and tested generalisation responses to different odours. Sixteen odours were used, which varied both in their functional group (primary and secondary alcohols, aldehydes and ketones) and in their carbon-chain length (from six to nine carbons).The results obtained by presentation of a total of 16 × 16 odour pairs show that (i) all odorants presented could be learned, although acquisition was lower for short-chain ketones; (ii) generalisation varied depending both on the functional group and the carbon-chain length of odours trained; higher generalisation was found between long-chain than between short-chain molecules and between groups such as primary and secondary alcohols; (iii) for some odour pairs, cross-generalisation between odorants was asymmetric; (iv) a putative olfactory space could be defined for the honeybee with functional group and carbon-chain length as inner dimensions; (v) perceptual distances in such a space correlate well with physiological distances determined from optophysiological recordings of antennal lobe activity. We conclude that functional group and carbon-chain length are inner dimensions of the honeybee olfactory space and that neural activity in the antennal lobe reflects the perceptual quality of odours.     

Olfactory receptors and odour coding

The first step of olfactory detection involves interactions between odorant molecules and neuronal protein receptors. Odour coding results from the combinatory activation of a set of receptors and rests on their clonal expression and olfactory neurone connexion, which lead to formation of a specific sensory map in the cortex. This system, sufficient to discriminate myriads of odorants with a mere 350 different receptors, allows humans to smell molecules that are not natural (new cooking flavours, synthetic chemicals...). The extreme olfactory genome diversity explains the absence of odour semantics. Olfactory receptors are also involved in cellular chemotaxis.     

Neural correlates of behavioural olfactory sensitivity changes seasonally in European starlings

Background

Possibly due to the small size of the olfactory bulb (OB) as compared to rodents, it was generally believed that songbirds lack a well-developed sense of smell. This belief was recently revised by several studies showing that various bird species, including passerines, use olfaction in many respects of life. During courtship and nest building, male European starlings (Sturnus vulgaris) incorporate aromatic herbs that are rich in volatile compounds (e.g., milfoil, Achillea millefolium) into the nests and they use olfactory cues to identify these plants. Interestingly, European starlings show seasonal differences in their ability to respond to odour cues: odour sensitivity peaks during nest-building in the spring, but is almost non-existent during the non-breeding season.

Methodology/Principal Findings

This study used repeated in vivo Manganese-enhanced MRI to quantify for the first time possible seasonal changes in the anatomy and activity of the OB in starling brains. We demonstrated that the OB of the starling exhibits a functional seasonal plasticity of certain plant odour specificity and that the OB is only able to detect milfoil odour during the breeding season. Volumetric analysis showed that this seasonal change in activity is not linked to a change in OB volume. By subsequently experimentally elevating testosterone (T) in half of the males during the non-breeding season we showed that the OB volume was increased compared to controls.

Conclusions/Significance

By investigating the neural substrate of seasonal olfactory sensitivity changes we show that the starlings'' OB loses its ability during the non-breeding season to detect a natural odour of a plant preferred as green nest material by male starlings. We found that testosterone, applied during the non-breeding season, does not restore the discriminatory ability of the OB but has an influence on its size.