'Floral' scent production by Puccinia rust fungi that mimic flowers

Crucifers (Brassicaceae) in 11 genera are often infected by rust fungi in the Puccinia monoica complex. Infection causes a 'pseudoflower' to form that is important for attracting insect visitors that sexually outcross the fungus. 'Pollinator' attraction is accomplished through visual floral mimicry, the presence of a nectar reward and floral fragrances. Here we used gas chromatography and mass spectrometry to identify and quantify fragrance production by these rust fungi on several Arabis hosts, and by co-occurring true flowers that share insect visitors. Fungal pseudoflowers produced distinctive floral fragrances composed primarily of aromatic alcohols, aldehydes and esters. Pseudoflower fragrances were chemically similar to noctuid-moth-pollinated flowers, such as Cestrum nocturnum and Abelia grandiflora , but were very different from host flowers, host vegetation and the flowers of coblooming, nonhost angiosperms. There was variation in the quantity and composition of fragrance profiles from different fungal species as well as within and among hosts. The evolution of scent chemistry is relatively conservative in these fungi and can be most parsimoniously explained in three steps by combining chemical data with a previously determined rDNA ITS sequence-based phylogeny. Pseudoflower scent does not appear to represent a simple modification of host floral or vegetative emissions, nor does it mimic the scent of coblooming flowers. Instead, we suspect that the unique fragrances, beyond their function as pollinator attractants, may be important in reducing gamete loss by reinforcing constancy among foraging insects.     

Application of the headspace gas chromatographic technique for continuous monitoring of the acetone-butanol-ethanol fermentation

An automatic, electropneumatic gas sampling system has been coupled to a gas chromatograph in order to monitor the acetone-butanol-ethanol fermentation. During calibration, signal responses for individual aqueous solutions of acetone, butanol and ethanol were linear up to 20 g l^?1, and negligible deviations from linearity were observed in aqueous solvent mixtures. Although dissolved salts in the medium increased individual solvent activity coefficients, these remained constant throughout the fermentation. After calibration, this quantitative gas chromatographic method proved suitable for rapid, continuous, accurate and precise monitoring of the fermentation.     

基于GC-IMS技术的不同红火蚁监测诱饵的风味成分分析

探讨不同红火蚁Solenopsis invicta Buren监测诱饵的风味成分,以期获得优化诱饵配方的科学依据。本文采用顶空气相色谱-离子迁移谱法分析不同红火蚁监测诱饵在60℃下的气味指纹图谱,并通过主成分分析法分析其风味物质的差异。结果共鉴定出93个信号峰和87种挥发性化合物,载体物质（CK）中具有较高强度峰的化合物包括3种苯、2种醇、3种酮、2种酯、4种醛、1种呋喃和1种烯;自主配制的诱饵（JR、ZR、JZ）的风味组成相似,较高强度峰的化合物包括2种醇、1种酸、12种醛和1-8桉叶素等;市售火腿肠（HT）中的3种烯、10种酮、1种苯、5种醛、1种呋喃、3种醚、7种醇和4种酯是具有较高强度峰的化合物。主成分分析表明,CK、HT与自主研发的诱饵聚集距离较远,三者均单独聚为一类,相互风味成分区别较大。综上所述,JR、ZR和JZ诱饵中醛类物质较多,而HT中酮类与醇类物质较为丰富。上述诱饵的风味成分分析结果能为研发精准高效的红火蚁监测专用诱饵提供重要信息。     

藏药镰形棘豆挥发性成分研究(英文)

本文通过水蒸气蒸馏、超临界CO2萃取和顶空萃取三种方法并结合GC和GC/MS技术分析藏药镰形棘豆(Oxytropis falcate Bunge)中的挥发性成分,共鉴定出58个化合物,分别占71.0%,85.6%和84.5%。烷烃类、黄酮类和醛类化合物为主要挥发性成分。3种方法得到的挥发性成分在保留时间值上具有一定的连续性,能更完全地阐述清楚藏药镰形棘豆的挥发性成分,为进一步开发利用这种药用植物提供科学依据。     

Onion aphid (Neotoxoptera formosana) attractants, in the headspace of Allium fistulosum and A. tuberosum leaves

Abstract:  Attractancy of Allium fistulosum L. and Allium tuberosum Rottl. to adult apterae of the onion aphid, Neotoxoptera formosana (Takahashi), an oligophagous aphid pest of Allium crops, was investigated with a Y-tube olfactometer. The aphids were significantly attracted to both A. fistulosum and A. tuberosum . The headspace components of both plants were extracted with solid-phase microextraction (SPME) and analysed by gas chromatography-mass spectrometry (GC-MS). The main volatile components of A. fistulosum were dipropyl disulphide (relative contents: 67%), 1-propenyl propyl disulphide (23%) and dipropyl trisulphide (6%). In the headspace of A. tuberosum , diallyl disulphide was detected as the main component (58%). Attractancy of dipropyl disulphide, dipropyl trisulphide and diallyl disulphide to the aphids was examined with the Y-tube olfactometer. The aphids were significantly attracted to dipropyl trisulphide and diallyl disulphide at a concentration of 0.01%. Dipropyl disulphide did not significantly attract the aphids at any concentrations tested. It was revealed that attractancy of A. fistulosum and A. tuberosum was caused by dipropyl trisulphide and diallyl disulphide, respectively. The findings suggest that N. formosana uses these sulphur compounds, characteristic components of Allium plants, as olfactory cues to find the host plants.     

Detection thresholds for phenyl ethyl alcohol using serial dilutions in different solvents

Detection thresholds are typically obtained by presenting a subject with serial dilutions of an odorant. Many factors, including the solvent used to dilute the odorant, can influence the measurement of detection thresholds. Differences have been reported in detection thresholds for phenyl ethyl alcohol (PEA) when different solvents are used. In this study we used gas chromatography (GC) to investigate further the effect of solvent on odor detection thresholds. We used a single ascending method and serial dilutions of PEA in four different solvents--liquid paraffin (LP), mineral oil (MO), propylene glycol (PG) and dipropylene glycol (DPG)--to determine the PEA thresholds for 31 adult subjects. For each solvent, we prepared eight serial log base 10 step dilutions (1-8), with corresponding liquid PEA concentrations of 6.3 x 10(1)-6.3 x 10(-6) (% v/v). We found that the threshold concentrations for PEA in LP (step 6.5) and PEA in MO (step 5.5) were significantly lower (P < 0.05) than for PEA in PG (step 4.0) and DPG (step 4.0) We then used GC to measure both the liquid and gas PEA concentrations for the dilution steps prepared with LP and PG. Although there were large threshold differences in the liquid concentrations of PEA in LP and PG, the headspace gas concentrations of PEA were the same. These results demonstrate the importance of determining the gas concentration of odorant stimuli when performing odor threshold measurements, in particular when comparing odor detection thresholds obtained using different solvents.     

Circadian rhythm of volatile emission from flowers of Nicotiana sylvestris and N. suaveolens

The volatile profiles from flowers of Nicotiana sylvestris and N. suaveolens were investigated by means of dynamic headspace sampling and capillary gas chromatography. Under conditions of light/dark entrainment both species emitted phenylpropanoid-derived volatiles (e.g. benzyl alcohol, methyl benzoate) with maximum emission occurring during the dark period. Emission of these compounds was demonstrated to be circadian by continuance of rhythmicity under conditions of constant light and subsequent re-entrainment to a new light/dark cycle. In contrast, emission of the sesquiterpene hydrocarbon, caryophyllene, from N. sylvestris followed no apparent pattern. The emission of monoterpene hydrocarbons from flowers of N. suaveolens showed diurnal differences only under conditions of light/dark entrainment.     

Comparative headspace analysis of cabbage plants damaged by two species ofPieris caterpillars: consequences for in-flight host location byCotesia parasitoids

Headspace composition, collected from intact cabbage plants and cabbage plants infested with eitherPieris brassicae L. orP. rapae L. (Lepidoptera: Pieridae) first instar larvae, was determined by GC-MS. Twenty-one volatiles were identified in the headspace of intact plants. Twenty-two volatiles were identified in the headspace of plants infested byP. brassicae larvae, 2 of which, Z-3-hexenyl butyrate and Z-3-hexenyl isovalerate, were not detected in the headspace of either intact orP. rapae damaged plants. In the headspace of the latter, 21 compounds were identified, all of which which were also produced by intact plants. No significant quantitative differences were found between headspace composition of the plants damaged by one or the other caterpillar species. Major differences between intact and caterpillar-damaged plants in contribution to the headspace profile were revealed for hexyl acetate, Z-3-hexenyl acetate, myrcene, sabinene and 1,8-cineole. The larval endoparasitoidCotesia glomerata L. was attracted by the volatiles emanating fromB. oleracea damaged byP. brassicae first instar larvae.C. rubecula L., a specialized larval endoparasitoids ofP. rapae, was attracted by the volatiles released from theB. oleracea-P. rapae plant-host complex. This shows that cabbage plants kept under the conditions of headspace collection produce attractive volatiles for both parasitoids.