Composition Of Floral Volatiles Research Articles

Floral scent of eastern skunk cabbage (Symplocarpus foetidus: Araceae)

Symplocarpus foetidus (L.) Salisb. (eastern skunk cabbage) occurs across a broad geographic range of northeastern North America, blooming in winter between December and March. The inflorescences are well-known for their thermogenic and thermoregulatory metabolic capabilities. The perceptual qualities of their fetid floral aroma have been described widely in the literature, but to date the floral volatile composition remained largely unknown. Here we present a detailed study of the floral scent produced by S. foetidus collected from intact female- and male-stage inflorescences and from dissected floral parts. Our results show a large range of biosynthetically diverse volatiles including nitrogen- and sulfur-containing compounds, monoterpenes, benzenoids, and aliphatic esters and alcohols. We document high inter-individual variation with some organ-specific volatile trends but no clear strong variation based on sexual stage. Multivariate data analysis revealed two distinct chemotypes from our study populations that are not defined by sexual stage or population origin. The chemotype differences may explain the bimodal perceptual descriptions in earlier work which vary between highly unpleasant/fetid and pleasant/apple-like. We discuss the results in ecological contexts including potential for floral mimicry, taking into account existing pollination studies for the species. We also discuss the results in evolutionary contexts, comparing our scent data to published scent data from the close sister species Symplocarpus renifolius. Future work should more closely examine the chemotype occurrence and frequency within these and other populations, and the impact these chemotypes may have on pollinator attraction and reproductive success.

Floral volatile composition of Jasminum sambac variants developed through colchicine

Jasmines are commercially grown for their fragrant flowers and essential oil. The present study investigates the composition of the volatile compounds from flowers of Jasminum sambac cv. Ramanthapuram Gundumalli and its variants that were evolved through colchicine. GC-MS analysis revealed that the flowers possessed major terpenes and sesquiterpenes such as Linalool, α-farnesene, germacrene-D, geranyl Linalool and D-Limonene as well as benzenoids (including benzyl acetate, benzyl alcohol and (Z)-Cinnamyl benzoate). The relative abundance of these volatile compounds in the variants have shown higher percentages than their wild-type (parent) which indicates that the variants possessed enhanced volatile composition. The new variations generated in floral volatile composition of J. sambac through polyploidisation are likely to have significant impact on the loose flower and perfume industries. Besides, the identified unique compounds can also be used as metabolic signatures to characterise the novel variants.

Taxonomic insights from floral scents of western North American sessile-flowered Trillium.

Chemical composition of floral volatiles can be an important complement to morphological characters in describing and identifying species. Four of the five species of western sessile-flowered Trillium are challenging to distinguish morphologically due to wide intraspecific variation and overlapping characters among taxa. Characterizing their floral volatile compositions could aid future taxonomic, ecological, and evolutionary studies of Trillium and related taxa. We addressed two major questions: How do western sessile Trillium taxa vary in floral chemistry? Can floral scent be used to distinguish species? We collected petals from 600 individuals at 42 wild populations of four sessile Trillium species across California, Oregon, and Washington. Volatile organic compounds from the petals were extracted using solid-phase microextraction, and the volatiles were identified and quantified by gas chromatography-mass spectrometry. The utility of floral scent composition in distinguishing species was tested using nonmetric multidimensional scaling and random forest analysis. Floral volatiles of the white-petaled T. albidum were dominated by oxygenated monoterpenes and showed considerable geographic variation that paralleled morphological variation. The maroon-petaled T. angustipetalum and T. kurabayashii produced floral scents characterized by aliphatic esters, but each had a distinct chemical composition. Petal color of Trillium chloropetalum is highly variable, as were its scent compositions, which were blends of volatiles from both white-petaled and maroon-petaled congeneric taxa. Differences in floral scent compositions are consistent with current taxonomy of the western sessile Trillium group. In cases where species delimitations are difficult based on morphology, floral scent composition provides taxonomic insight and suggests a potential hybrid origin for T. chloropetalum.

Critical Pollination Chemistry: Specific Sesquiterpene Floral Volatiles in Carrot Inhibit Honey Bee Feeding.

Many plants rely on insect pollination, yet numerous agricultural plant-breeding programs focus on traits that appeal to growers and consumers instead of pollinators, leading to declining pollinator attraction and crop yields. Using hybrid carrot seed production as a model, we investigated low-yielding carrot varieties by analyzing sugars and minerals in nectar and floral volatile composition. While the analysis of nectar sugars and minerals did not reveal any key differences between the carrot varieties, differences between the 112 detected volatiles in 23 samples were observed. Numerous differentiating sesquiterpenes were identified in floral solvent extracts, and subsequent behavioral assays showed that β-ocimene from higher-yielding carrot varieties stimulated nectar feeding (attractant), while α- and β-selinene from lower-yielding lines decreased feeding (deterrents). Sesquiterpenes have previously been implicated in plant defense, suggesting a trade-off between pollination and protection. Our results highlight the importance of volatiles as regulators of pollinator attraction in agricultural settings.

Reproductive biology of Piper species (Piperaceae): a review to link the past to the future

Abstract Piper species are important components of the understory in tropical and subtropical forests, and some species are of economic and medicinal importance. This genus has been studied in different areas of science. However, some questions remain unanswered after the new circumscription as proposed by phylogenetic studies. Here, I review different aspects related to the reproductive biology of Piper species (phenology, sexual expression, floral biology, pollination and mating systems), comparing the results between Neotropical (representing most of the studies carried out so far) and Paleotropical regions. Seventy-five species were analyzed. Some patterns can be observed, mainly in Neotropical species, such as the predominance of annual flowering and fruiting, dichogamy (generally incomplete protogyny) with gradual and sequential exposure of stigmas, asynchronous pollen release, and pollination by insects. Some aspects have been poorly studied, such as variations in sexual expression, the efficiency of different pollinators, and the chemical composition of floral volatiles associated with their role in pollination. In addition, I discuss remaining gaps and further studies that are required, mainly on Paleotropical Piper species, to obtain basic information on the reproductive biology of these plants. From this, comparisons with Neotropical species can be made, allowing the verification of patterns in this genus.

Genotype, mycorrhizae, and herbivory interact to shape strawberry plant functional traits.

Arbuscular mycorrhizal fungi (AMF) and herbivores are ubiquitous biotic agents affecting plant fitness. While individual effects of pairwise interactions have been well-studied, less is known about how species interactions above and belowground interact to influence phenotypic plasticity in plant functional traits, especially phytochemicals. We hypothesized that mycorrhizae would mitigate negative herbivore effects by enhancing plant physiology and reproductive traits. Furthermore, we expected genotypic variation would influence functional trait responses to these biotic agents. To test these hypotheses, we conducted a manipulative field-based experiment with three strawberry (Fragaria x ananassa) genotypes to evaluate plant phenotypic plasticity in multiple functional traits. We used a fully-crossed factorial design in which plants from each genotype were exposed to mycorrhizal inoculation, herbivory, and the combined factors to examine effects on plant growth, reproduction, and floral volatile organic compounds (VOCs). Genotype and herbivory were key determinants of phenotypic variation, especially for plant physiology, biomass allocation, and floral volatiles. Mycorrhizal inoculation increased total leaf area, but only in plants that received no herbivory, and also enhanced flower and fruit numbers across genotypes and herbivory treatments. Total fruit biomass increased for one genotype, with up to 30-40% higher overall yield depending on herbivory. Herbivory altered floral volatile profiles and increased total terpenoid emissions. The effects of biotic treatments, however, were less important than the overall influence of genotype on floral volatile composition and emissions. This study demonstrates how genotypic variation affects plant phenotypic plasticity to herbivory and mycorrhizae, playing a key role in shaping physiological and phytochemical traits that directly and indirectly influence productivity.

Floral Scent Composition and Fine-Scale Timing in Two Moth-Pollinated Hawaiian Schiedea (Caryophyllaceae).

Floral scent often intensifies during periods of pollinator activity, but the degree of this synchrony may vary among scent compounds depending on their function. Related plant species with the same pollinator may exhibit similar timing and composition of floral scent. We compared timing and composition of floral volatiles for two endemic Hawaiian plant species, Schiedea kaalae and S. hookeri (Caryophyllaceae). For S. kaalae, we also compared the daily timing of emission of floral volatiles to evening visits of their shared pollinator, an endemic Hawaiian moth (Pseudoschrankia brevipalpis; Erebidae). The identity and amount of floral volatiles were measured in the greenhouse during day and evening periods with dynamic headspace sampling and GC-MS (gas chromatography – mass spectrometry). The timing of emissions (daily rise, peak, and fall) was measured by sampling continuously for multiple days in a growth chamber with PTR-MS (proton transfer reaction mass spectrometry). Nearly all volatiles detected underwent strong daily cycles in emission. Timings of floral volatile emissions were similar for S. kaalae and S. hookeri, as expected for two species sharing the same pollinator. For S. kaalae, many volatiles known to attract moths, including several linalool oxides and 2-phenylacetaldehyde, peaked within 2 h of the peak visitation time of the moth which pollinates both species. Floral volatiles of both species that peaked in the evening were also emitted several hours before and after the brief window of pollinator activity. Few volatiles followed a daytime emission pattern, consistent with increased apparency to visitors only at night. The scent blends of the two species differed in their major components and were most distinct from each other in the evening. The qualitative difference in evening scent composition between the two Schiedea species may reflect their distinct evolutionary history and may indicate that the moth species uses several different floral cues to locate rewards.

Pollinator Preferences for Floral Volatiles Emitted by Dimorphic Anthers of a Buzz-Pollinated Herb

Floral scents attract pollinators to plant rewards; in nectarless flowers, pollen grains are the only reward. Thus, pollen not only fertilizes ovules, but also feeds pollinators. This dilemma is resolved by specialization of anthers (i.e., heteranthery): feeding anthers that feed pollinators and pollinating anthers for fertilization. We hypothesized that the chemical composition of floral volatiles differs between the two types of anther and influences pollination preference for feeding anthers. We used Solanum rostratum as a study model because its heterantherous flowers produce a floral scent that suggests a close association with their pollinators. The main aim of this study was to determine the chemical composition of the two types of anther and to investigate how they influence foraging behaviour of pollinators. To characterize this composition, we used solid phase microextraction and hexane extraction followed by gas chromatography-mass spectrometry. We registered 12 volatile compounds in S. rostratum floral extracts, mainly aromatic and sesquiterpene compounds. The proportion of these compounds differed between feeding and pollinating anthers. Some of these compounds were probably emitted by osmophores located in both anther types. Also, we used electroantennography to investigate Melipona solani antennal response to floral volatiles. The M. solani antennae are receptive to the highest floral extract dose tested. Finally, we conducted two behavioural bioassays to test bee attraction for each type of floral extract: a) multiple-choice in a feeding arena using M. solani and b) Y-olfactometer bioassay using Bombus impatiens. Both bee species preferred feeding anthers in bioassays. In conclusion, heteranthery involves chemical differentiation (i.e., proportion of volatiles compounds) in anther specialization that influences bee preference for feeding anthers over pollinating anthers.

Jatropha curcas flowers from southern Mexico: chemical profile and morphometrics

Jatropha curcas flowers from two localities in the Soconusco region, southern Mexico, were chemical and morphometrically analyzed: Camino a la Pita (CP) and Manuel Lazos (ML). Our results showed significant differences in floral volatile composition and flower morphology. A total of 30 compounds were identified; (E)-β-ocimene was the main compound in all flowers, followed by dendrolasin, (Z, E)-α-farnesene, linalool, and (3Z)-hexenyl benzoate. (Z, E)-α-farnesene was the first discriminant compound between flower sex and locations, followed by (3Z)-hexenyl benzoate, (cis)-β-elemenone and linalool based on the Gini index. Morphometrically, there were significant differences between study sites, where CP female flowers were smaller in sepal, petal length and gynoecium height. These phenotypic variations could be the consequence of the high genetic differentiation driven for the environmental conditions where these populations are grown.

Floral scent emitted by white and coloured morphs in orchids

Polymorphism of floral signals, such as colour and odour, is widespread in flowering plants and often considered to be adaptive, reflecting various pollinator preferences for particular floral traits. Several authors have recently hypothesized that particular associations exist between floral colour and scent, which would result from shared biochemistry between these two floral traits. In this study, we compared the chemical composition of floral volatiles emitted by white- and purple-flowered morphs of three different orchid species, including two food-deceptive species (Orchis mascula and Orchis simia) and a food-rewarding species (Anacamptis coriophora fragrans). We found clear interspecific differences in floral odours. As expected from their pollination strategy, the two deceptive orchids showed high inter-individual variation of floral volatiles, whereas the food-rewarding A. c. fragrans showed low variation of floral scent. Floral volatiles did not differ overall between white- and coloured-flowered morphs in O. mascula and A. c. fragrans, while O. simia exhibited different volatile profiles between the two colour morphs. However, a detailed analysis restricted to benzenoid compounds (which are associated with the production of floral anthocyanin pigments) showed that white inflorescences emitted more volatiles of the shikimic pathway than coloured ones, both for O. mascula and O. simia. These results are consistent with the current hypothesis that shared biochemistry creates pleiotropic links between floral colour and scent. Whether intraspecific variation of floral signals actually affects pollinator attraction and influences the reproductive success of these orchids remains to be determined.

Floral volatile composition of four species of Vaccinium1This article is part of a Special Issue entitled “A tribute to Sam Vander Kloet FLS: Pure and applied research from blueberries to heathland ecology”.

The floral volatile composition of four species of Vaccinium was profiled to asses the diversity of the floral chemistry within this genus. Flowers of Vaccinium angustifolium Aiton, Vaccinium varingiaefolium Miq., Vaccinium arboreum Marsh., and Vaccinium poasanum Donn. Sm. were sampled from three or more plants, and volatiles were collected and analyzed by gas chromatography – mass spectroscopy. A total of 45 volatile compounds were detected in the air (headspace) surrounding flowers including 40 from V. angustifolium, 34 for V. varingiaefolium, 37 for V. arboreum, and 17 for V. poasanum. Of the volatile compounds identified, 34 were terpenoids, 6 were benzoids and phenylpropanoids, 4 were aliphatics, and 1 was a miscellaneous cyclic compound. Terpenoids accounted for 98%, 80%, 76%, and 67% of the total volatiles for V. angustifolium, V. varingiaefolium, V. arboreum, and V. poasanum, respectively. The most abundant volatile compound emitted from the flowers of each species was α-pinene for V. angustifolium (23%) and V. arboreum (63%), methyl benzoate for V. varingiaefolium (18%), and ethyl benzene for V. poasanum (21%). Substantial variation was observed in the floral volatile composition of these four Vaccinium species, which may reflect their diverse ecological origins.

Rare white‐flowered morphs increase the reproductive success of common purple morphs in a food‐deceptive orchid

How floral colour polymorphism can be maintained in evolutionary time is still debated. In rewardless orchids, it is unknown whether rare white-flowered morphs differ in scent chemistry from pigmented morphs, and whether such intraspecific variation in floral signals may have an impact on reproductive success. We compared the chemical composition of floral volatiles emitted by white- and purple-flowered morphs of Orchis mascula, and recorded the fruit set of both colour morphs. We also used white ping-pong balls to mimic white-flowered morphs in field bioassays. We found that colour polymorphism was not associated with floral odour polymorphism. Surprisingly, when populations of purple-flowered plants included a few white-flowered individuals, the fruit set of the purple morph increased significantly (from 6 to 27%), while that of the white morph remained low. We obtained the same fourfold increase in fruit set when using ping-pong balls as visual lures, demonstrating the association between colour variation and fruit set, and the key role of visual signals in pollinator attraction. Our results are incompatible with negative frequency-dependent selection, a hypothesis invoked to explain colour polymorphism in other rewardless orchids. We propose several hypotheses to explain the maintenance of white morphs in O. mascula.

Integrating floral scent, pollination ecology and population genetics

Summary1. Floral scent is a key factor in the attraction of pollinators. Despite this, the role of floral scent in angiosperm speciation and evolution remains poorly understood. Modern population genetic approaches when combined with pollination ecology can open new opportunities for studying the evolutionary role of floral scent.2. A framework of six hypotheses for the application of population genetic tools to questions about the evolutionary role of floral scent is presented. When floral volatile chemistry is linked to pollinator attraction we can analyse questions such as: Does floral volatile composition reflect plant species boundaries? Can floral scent facilitate or suppress hybridization between taxa? Can the attraction of different pollinators influence plant mating systems and pollen‐mediated gene flow? How is population genetic structure indirectly influenced by floral scent variation?3. The application of molecular tools in sexually deceptive orchids has confirmed that volatile composition reflects species boundaries, revealed the role of shared floral odour in enabling hybridization, confirmed that the sexual attraction mediated by floral odour has implications for pollen flow and population genetic structure and provided examples of pollinator‐mediated selection on floral scent variation. Interdisciplinary studies to explore links between floral volatile variation, ecology and population genetics are rare in other plant groups.4. Ideal study systems for future floral scent research that incorporate population genetics will include closely related taxa that are morphologically similar, sympatric and co‐flowering as well as groups that display wide variation in pollination mechanisms and floral volatiles.

Effects of florivory on floral volatile emissions and pollination success in the wild parsnip

In addition to reducing fitness by consuming reproductive structures, florivores may also reduce plant fitness by altering interactions with pollinators. To date, the effects of florivore activity on the volatile profile of flowers and subsequent attractiveness to pollinators have not been extensively investigated. In this study, we had three specific objectives: to determine the impact of florivory by the parsnip webworm Depressaria pastinacella on the floral volatile profile of the wild parsnip Pastinaca sativa, to ascertain the mechanisms by which florivory changes the volatile profile, and to estimate the consequences of florivory on visitation by pollinators and eventual seed set. An overall indirect effect of webworms on seed set, that is, the effect of infestation on pollination success, was not detected. However, this overall lack of indirect effect masks the heterogeneity among individual plants. For seven of 14 plants examined, pollination success was altered by webworms, and in four of these plants the alteration in pollination success was consistent with webworm-altered visitation. Webworms significantly altered floral fragrance, in particular causing disproportionate increases in the emissions of octyl esters. Additionally, volatiles from webworm frass, which contains large amounts of the octyl ester metabolite n-octanol, may alter the floral fragrance in ways that change attractiveness of flowers to pollinators. This study suggests that the effects of florivores on plant fitness are not limited to the removal of floral units but may also involve alterations in floral volatile composition, through damage-induced release and detoxification of particular constituents, that affect visitation and pollination success.

The ecological and taxonomic importance of flower volatiles of Clusia species (Guttiferae)

The chemical composition of floral volatiles of sixteen species of Clusia (Guttiferae) belonging to four different taxonomic sections of the genus was investigated. The volatiles were extracted from fresh petals by microhydrodistillation and analysed by GC/MS. The composition of the volatiles was in part, but not always, related to the taxonomic position of the species, and to a minor extent to the type of pollinator observed on the flowers as revealed by clustering analysis. The composition of the volatile components of female and male flowers belonging to the same species ( C. grandiflora, C. lanceolata, C. paralicola, C. parviflora and C. spiritu-sanctensis) was found to be almost identical. Field bioassays showed the petal extracts to be attractive to pollinating bees.

The Pollination Biology of Tuckahoe, Peltandra virginica (Araceae)

This study describes the specialized brood-site-based pollination system of Peltandra virginica Kunth (Araceae) with the chloropid fly Elachiptera formosa Loew and provides experimental evidence that gender-related changes in floral odor composition synchronize pollinator behavior with the blooming sequence. P. virginica is protogynous and does not self-pollinate because of a strong temporal separation in sexual function, and it is dependent upon insects for pollination because the spathe completely surrounds the spadix during the pistillate stage. Field observations conducted in central New Jersey and southeastern Pennsylvania showed that E. formosa is closely associated with P. virginica inflorescences. Within the floral chamber, E. formosa adults feed on pollen, mate, and find oviposition sites while the larvae complete their development. Although drosophilid and syrphid flies were collected and reared from inflorescences of both sexual stages, only E. formosa emerged from pistillate-stage inflorescences and adult E. formosa rapidly transferred fluorescent dye particles between inflorescences of both sexual stages in laboratory enclosures. These findings indicate that this fly species is the primary pollinator at our study locations. Field censuses demonstrated that although E. formosa visited P. virginica inflorescences of both sexual stages with equal frequency, the female flies preferentially oviposited within pistillate-stage inflorescences. Analysis of floral volatiles with gas chromatography-mass spectrometry showed that only the spathes emit the floral fragrance and that the composition of the floral volatiles changed during the transition from pistillate to staminate stage. A particularly noticeable change occurred in the emission ratio of the two primary floral odor components, 4,5,7-trimethyl-6,8-dioxabicyclo[3.2.1.]octane and an unidentified chemical analog with molecular weight of 142. The relationship between floral volatile composition and fly oviposition behavior was evaluated using sham inflorescences placed in the P. virginica study population. The sham inflorescences were constructed by covering spadices dissected from mature inflorescence buds with spathes excised from different-age inflorescences. After a 2-hr-long exposure period, sham inflorescences fitted with pistillate-stage spathes contained more E. formosa eggs than the sham inflorescences with staminate-stage spathes. However, the highest number of ovipositions occurred in sham inflorescences fitted with spathes excised from mature inflorescence buds. The fragrance emitted by these spathes was composed almost entirely of the two principal odor components. The decline in ovipositions observed in both real and sham inflorescences corresponded to an increase in the emission ratio of 4,5,7-trimethyl-6,8-dioxabicyclo[3.2.1.]octane to the molecular weight 142 analog. This suggests that gravid flies searching for oviposition sites used the ratio of the two primary floral volatile components as an inflorescence gender or age recognition cue.