Floral Scent Composition Research Articles

Strong Conservation of Floral Scent Composition in Two Allopatric Yuccas

Floral scent has been suggested to play a key role in the obligate pollination mutualism between yuccas and yucca moths. We analyzed floral fragrance compounds of Yucca elata with headspace collection followed by gas chromatography and mass spectrometry, and compared the odor blend with the recently characterized blend of the allopatric Yucca filamentosa. A principal component analysis based on 20 scent compounds revealed that the floral odor bouquets of Y. elata and Y. filamentosa are virtually identical. Although the two plants belong to the same section of capsular-fruited yuccas, they rely on different species of Tegeticula moths for pollination and probably have been allopatric for several million years. Yet, their floral odor blends are very similar, which may indicate that strong selection by obligate pollinators counteracts drift or divergence in this trait.

Chemistry and geographic variation of floral scent in Yucca filamentosa (Agavaceae)

We identified volatiles from the floral headspace of Yucca filamentosa using gas chromatography and mass spectrometry and analyzed floral scent composition and variation among populations pollinated by different yucca moth species. Twenty-one scent compounds were repeatedly identified and most could be categorized into two major classes: (1) homoterpenes derived from the sesquiterpene alcohol nerolidol and (2) long chain aliphatic hydrocarbons. Two biosynthetic pathways are thus responsible for the majority of floral volatiles in Y. filamentosa. The homoterpene E-4,8-dimethylnona-1,3,7-triene, which is released systemically by higher plants upon herbivory, was the most abundant compound. Two di-oxygenated compounds not previously reported as floral compounds also were detected. No differentiation in floral scent was observed between populations pollinated by different yucca moths, nor was there any correlation between chemical distance and geographic distance among populations. The total release rate of volatiles differed significantly among populations, but not between populations with different pollinators. The combination of unique compounds and low variation in the fragrance blend may reflect highly selective attraction of obligate pollinators to flowers. The observed lack of differentiation in floral scent can putatively explain high moth-mediated gene flow among sites, but it does not explain conservation of odor composition across populations with different pollinators.

THE SCENT OF A MALE: THE ROLE OF FLORAL VOLATILES IN POLLINATION OF A GENDER DIMORPHIC PLANT

Most flowering plants rely on animal pollinators to transfer male gametes between individuals, and thus a significant problem for gender dimorphic plants is that pollinators often avoid female flowers. Here we show for the first time that one important reason pollinators shun female flowers is because they do not smell like males. We compared emission rates and floral scent composition in a gynodioecious wild strawberry (Fragaria virginiana) where females receive half as many visits by generalist pollinators as conspecific hermaphrodites. We used floral extracts to determine the source of sexually dimorphic odor and pollinator responses. Specifically, we used extracts of whole flowers and specific floral parts in choice tests to determine that pollinators preferred the scent of hermaphrodite flowers over those of females and that this discrimination was due primarily to the scent of hermaphrodite anthers. These data conclusively show that scent can be a major driver of pollinator behavior in gender dimorphic plants. Our results also indicate that scent is an important modulator of pollinator behavior even in a small flowered, weakly scented species visited by generalist pollinators, and not just peculiar to intensely scented, deceptive, or specialized pollination systems.

Qualitative and quantitative analyses of flower scent in Silene latifolia

The quantitative and qualitative variability in floral scent of 98 specimens of the dioecious species Silene latifolia belonging to 15 European and 19 North American populations was determined. Floral scent was collected from single flowers using dynamic headspace methods, and analysed by Micro-SPE and GC-MS methods. The flowers showed a nocturnal rhythm, and scent was emitted only at night. The amount of emitted volatiles varied greatly during the season, from 400 ng/flower/2 min in June to 50 ng/flower/2 min in August and September. The qualitative variability in the floral scent was high and different chemotypes, characterised by specific scent compounds, were found. Female and male flowers emitted the same type and amount of volatiles. The differences in floral scent composition between European and North American populations were small. Typical compounds were isoprenoids like lilac aldehyde isomers, or trans-β-ocimene, and benzenoids like benzaldehyde, phenyl acetaldehyde, or veratrole. Some of these compounds are known to attract nocturnal Lepidoptera species. The high qualitative variability is discussed in relation to the pollination biology of S. latifolia, and the results are compared with other studies investigating intraspecific variability of flower scent.

Trends in floral scent chemistry in pollination syndromes: floral scent composition in hummingbird-pollinated taxa

We studied an assemblage of 17 species of bird-pollinated Ecuadorian plants (from 14 angiosperm families), including taxa pollinated by short-billed (trochiline) and sickle-billed (hermit) hummingbirds. Hummingbirds are widely supposed to ignore fragrance while visiting flowers. We collected floral headspace odours in order to test the general prediction that specialist hummingbird-pollinated flowers are scentless. In nine out of 17 of these species we failed to detect any odours using gas chromatography-mass spectrometry (GC-MS), whereas the remaining eight species produced trace levels of volatile compounds. Most of these odour compounds were of terpenoid or lipoxygenase derivation and are commonly emitted by vegetative as well as floral plant tissues. Further studies will be required to determine whether these weak odours attract alternative pollinators, repel enemies or represent vestiges of a scented ancestry.

Flower scent composition in diurnal Silene species (Caryophyllaceae): phylogenetic constraints or adaption to flower visitors?

A comparative analysis of the flower volatiles of 10 day-flowering Silene species native to Central Europe was made to improve the understanding of the pollination biology and evolution of floral odours in the genus. Floral scent was collected by dynamic headspace adsorption and analysed via gas chromatography–mass spectrometry. In total, 60 compounds could be identified by their mass spectra as well as by their relative retention times. The number of compounds per species ranged between 16 in Silene rupestris and 40 in S. viscaria. Main compounds in most species were fatty acid derivatives (FADs, cis-3-hexen-1-ol, cis-3-hexenyl acetate, n-nonanal), benzenoids (benzaldehyde, phenylacetaldehyde, methyl benzoate), and monoterpenes (limonene, linalool), accompanied by sesquiterpenes, and nitrogen-containing compounds. Nonmetric multidimensional scaling (CNESS, NMDS) based on relative amounts of single components leads to the same conclusion as visualization of similarities based on component classes reflecting to some degree biosynthetic pathways: differences in floral scent composition can be related to both the taxonomy and the pollination biology of the species investigated. In all but one species of the Silene group, and all species of the Lychnis group ( S. dioica, S. flos-cuculi, S. flos-jovis, S. pendula), the dominating compound classes are benzenoids followed by FADs. The relatively high amounts of aromatic compounds (e.g. benzaldehyde, phenylacetaldehyde, methyl benzoate) are indicative of an adaptation towards butterfly pollination. Species of the Viscaria and Eudianthe groups showed high relative amounts of FADs but a lower content of benzenoids. Relatively high amounts of monoterpenes (>10%) were found in S. alpestris, S. coeli-rosa, S. gallica, and S. viscaria. It is suggested that the high relative content of the most volatile monoterpene alkenes (e.g. limonene) in S. gallica and S. coeli-rosa may be indicative of an adaptation to bees as pollinators in these species.

Floral scent of bat-pollinated species: West Africa vs. the New World

Floral scent of seven West African bat-pollinated tree species, belonging to six families, was collected in situ from flowering individuals using headspace adsorption. The seven species shared neither any specific compounds nor any other discernible pattern in their floral scent composition. Most of the identified compounds are common in the floral scent of species pollinated by a variety of animals. Adansonia digitata (Bombacaceae) was the only African species found to have a substantial proportion of sulphur compounds in its floral scent. This feature contrasts with the sampled New World bat-pollinated plants, which frequently contain these compounds. The floral scent of Ceiba pentandra (Bombacaceae), native to both South America and Africa, contained no sulphur substances, contradicting a previous study in the New World that identified the major floral compounds as dimethyl disulphide and dimethyl trisulphide. We suggest that the differences in the floral scent of C. pentandra, including the absence of sulphur compounds in the African variety, result from the different selective regimes exerted by the Pteropotidae bats, in Africa, and Phyllostomidae bats, in the New World, that visit their flowers. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82, 161–168.

Nectar sugar composition and floral scent compounds of diurnal and nocturnal Conophytum species (Aizoaceae)

The putative correlation between nectar sugar composition, floral scent compounds, and the pollination syndrome (diurnal vs nocturnal) was evaluated in the genus Conophytum (Aizoaceae). Nectar sugar compositions of 39 species, subspecies, and varieties of the genus Conophytum were analysed via high performance liquid chromatography (HPLC). Nectar contained mainly glucose and fructose and in several cases small amounts of sucrose. In all Conophytum species investigated nectar is hexose-dominant, or at least hexose-rich. An interesting variation in the fructose:glucose ratio was observed — samples of diurnal species had significantly higher fructose:glucose ratios than samples of nocturnal species. Floral scents of 27 diurnal and nocturnal Conophytum species from 11 sections were collected by headspace adsorption and analysed via gas chromatography–mass spectrometry (GC-MS). In total 33 compounds could be identified by their mass spectra as well as by their relative retention times. Most of the species were dominated by only a few (3–5) floral scent compounds. The species showed basic similarities in being dominated by benzenoids accompanied by fatty-acid derivatives, nitrogen-containing compounds, and terpenoids. The floral scent composition of all species was dominated by benzaldehyde and benzeneacetaldehyde. Compared to nocturnal species, diurnal species are characterised by a lower number of compounds, low amounts of aromatic esters, and an almost total absence of nitrogen-containing compounds. It is assumed that the relatively high amounts of aromatic esters in the scent of some nocturnal species are an adaptation to moth pollination.

Variation in floral scent composition within and between populations of Geonoma macrostachys (Arecaceae) in the western Amazon

In geonomoid palms floral scent is both an important pollinator attractant and an important factor in reproductive isolation. However, little is known about intraspecific variation in floral scent composition in these as well as in other plants. In this study the level of variation in floral scent composition found within and among five populations of Geonoma macrostachys var. macrostachys in the western Amazon is documented. Floral scent samples were collected using head-space adsorption and were analyzed by gas chromatography-mass spectrometry. Most of the 108 compounds recorded were of isoprenoid origin, but only 28 of the compounds were found in all 62 samples analyzed. No differentiation was found between the studied populations, confirming that G. macrostachys var. macrostachys is outbreeding and indicating that the individual populations are part of a metapopulation linked by sufficient gene flow to avoid local differentiation. However, a negative correlation between distance and similarity of floral scent chemistry indicates a case of clinal variation within the distribution area of G. macrostachys. Male euglossine bees are infrequent visitors to G. macrostachys, while other groups of insects are abundant. However, the level of variation and the chemical composition lend support to a suggested importance of male euglossine bees in long-distance pollen flow in G. macrostachys. Other insect groups are probably important in securing pollination of most flowers with pollen from nearby sources.

Floral scents in butterfly-pollinated plants: possible convergence in chemical composition

The study explores whether or not there are convergent patterns in floral scent composition among plant species that completely or partially rely on butterflies for pollination. Floral scent compounds were analysed from 22 flowering butterfly-pollinated plant species, representing 13 families which originate mainly from temperate North Europe but also from tropical and temperate America. Scents were collected using the dynamic headspace adsorption method and identified with coupled gas chromatography and mass spectrometry (GC-MS). In total, 217 floral scent compounds were identified, with the number per species ranging from 8 to 65. The major emerging pattern is the occurrence of certain compounds emitted exclusively by the flowers of many of the investigated species in major amounts – the benzenoids phenylacetaldehyde and 2-phenylethanol, the monoterpenes linalool and linalool oxide (furanoid) I and II and the irregular terpene oxoisophorone. It is likely that these compounds serve as a signal to attract pollinating butterflies, and may have evolved in conjunction with the sensory capabilities of butterflies as a specific group of pollinators. While there is convergence in terms of the compounds sharing this function there has been a geographical divergence in terms of their relative abundance. The predominance (in terms of both numbers and relative amount) of benzenoids in many of the scent blends of the European temperate species and of linalool and its derivatives in those of the American species constitute two discernible groups among these plants. © 2002. The Linnean Society of London, Botanical Journal of the Linnean Society, 2002, 140, 129–153.

Biochemical and molecular genetic aspects of floral scents.

The chemical composition of floral scents has been extensively investigated for hundreds of years because of the commercial value of floral volatiles in perfumery. More recently, several ecological studies have examined the roles of floral scent in the biology of the plant. However, in contrast to

Floral scent differentiation among coflowering, sympatric species ofGeonoma(Arecaceae)

AbstractThis paper presents an investigation of the chemical composition of the floral scent of eight coflowering, sympatric taxa ofGeonoma, a neotropical genus of understory palms with little or no variation in floral characteristics. The objective was to evaluate if floral scent might function as a reproductive isolation mechanism. Floral scent was collected with headspace techniques and the chemical composition analyzed and determined by gas chromatography–mass spectrometry. The eight studied taxa each had a characteristic, distinct floral scent composition, as revealed by grouping of individuals of each taxon together in a principal component analysis. As flower morphology and colors, as well as the diurnal flowering phenology, often vary little between sympatric, coflowering plants, other mechanisms to keep the species reproductively isolated are needed. It was concluded that variation in floral scent composition potentially is of importance to keep taxa ofGeonomareproductively isolated.

Floral Scent Attraction in Geonoma macrostachys, an Understorey Palm of the Amazonian Rain Forest

The flowers of Geonoma macrostachys, a monoecious, neotropical, understorey palm, produce a strong floral scent and are visited by beetles, flies, and bees. To study the importance of floral scent in the attraction of insects to G. macrostachys, a biotest with natural scented and non-scented inflorescence models was set up in the field. Variation in floral scent composition was studied diurnally as well as between staminate and pistillate flowers and individuals. Floral scent was collected using headspace methods and was analysed by combined gas chromatography-mass spectrometry. The natural scented inflorescence models attracted significantly (p<0.0001) more insects than the non-scented models. Although the total amount of floral scent produced decreased steadily during the daily flowering, individual compounds showed three patterns of variation: a steady decrease, an increase during the morning followed by a steady decrease, and an increase during the morning and midday followed by a steady decrease. The variation in chemical composition of the floral scent of staminate and pistillate flowers on the same individual was as large as it was between all pistillate and staminate samples and individuals investigated. The diurnal variation in floral scent production and composition is hypothesized to be related to a daily variation in the visiting fauna. Due to floral scent collection on both staminate and pistillate flowers male euglossine bees are regarded as potentially important pollinators of G. macrostachys. However. G. macrostachys rely partly on a deceptive pollination strategy, since, for all visitors except male euglossine bees the pistillate flowers contain no reward.

Floral scents of hawkmoth-pollinated flowers in Japan

Similarity among the floral scents of hawkmoth-pollinated plants was investigated with headspace samplings. Six of seven plant species belonging to different families were found to be rich in isoprenoids, among which linalool was the most common compound. Linalool showed rhythmicity with a nocturnal increase inLonicera japonica. These findings suggest that linalool is a common attractant for nocturnal hawkmoths. However, the composition of other isoprenoids, benzenoids and fatty acid derivatives varied markedly among the plant species examined. There was a significant correlation between species composition of flower-visiting hawkmoths and specific floral scents, suggesting that attractiveness to each hawkmoth species is dependent upon floral scent.

Floral Scent and Pollination in Browneopsis disepala (Leguminosae: Caesalpinioideae) in Western Ecuador

Aspects of the pollination ecology of Browneopsis disepala, including floral scent composition, were studied. Floral scent was collected with head space techniques and analyzed by coupled gas chromatography-mass spectrometry. Inflorescence and flower development were followed, and amount and concentration of nectar measured. Flower-visiting animals were observed nocturally and diurnally. Inflorescences of B. disepala emit a floral scent that is typical of neither moth- nor bat-pollinated plants, but contains some compounds related to both pollination types. Nectar is produced in quantities and with sugar concentrations falling within a range typical of both moth- and bat-pollinated plants. The inflorescences are visited by both moths and bats, but the behavior of the bats suggests that they are the more efficient pollinators. Browneopsis disepala has a mixed pollination system and is dependent on animals for pollination.

Floral scent variation in the Pyrola rotundifolia complex in Scandinavia and Western Greenland

The variation in floral scent composition within and among populations of four taxa belonging to the Pyrola rotundifolia complex was analyzed using Principal Component Analysis. Two major groups were recognized, P. norvegica and P. grandiflora on the one side and P. rotundifolia s. str. on the other. Benzaldehyde dominated the scent of the first group and methoxy benzenes and phenyl propanoids that of the second group. A large variation in the floral scent chemistry was found both within some of the studied populations as well as among them. The floral scent composition of P. rotundifolia ssp. maritima was no more different from P. rotundifolia ssp. rotundifolia, than the differences between populations of P. rotundifolia ssp. rotundifolia. The findings are in partial agreement with the current delimitation of the taxa in the P. rotundifolia complex.

Floral odours in the Theophrastaceae

Floral scent was collected by head-space adsorption from seven species of the Theophrastaceae, viz. Theophrasta americana, Deherainia smaragdina, Jacquínia keyensis, J. macrocarpa, J. sprucei, Clavija euerganea and C. repanda. The chemical composition of the floral scent was determined with coupled gas chromatography-mass spectrometry (GC-MS). The floral scent composition accord with the generic delimitation within the Theophrastaceae; Theophrasta is characterized by a fatty acid derived alcohol and an acid, Deherainia by fatty acid derived esters and an acid, and pyrazines, Jacquinia by benzenoids and phenyl propanoids with additionally trimethylcyclohexanes-derivatives of carotenoids in the orange-flowered species ( J. macrocarpa, J. sprucei), and Clavija mainly by sesquiterpene hydrocarbons. We suggest that the trimethylcyclohexenes in the floral scent of the orange-flowered Jacquinia species are formed during anthesis through degradation of carotenoids in the corolla pigments. Floral morphology and scent chemistry suggest that Theophrasta and Deherainia are sapromyophilous, while Jacquinia and Clavija are melittophilous. Melittophily is suggested to be the ancient condition in the family, while the derived condition, sapromyophily, may have evolved independently in Deherainia and Theophrasta.

A multivariate approach to post‐pollination changes in the floral scent of Platanthera bifolia (Orchidaceae)

The effect of pollination on floral scent composition and production in the moth‐pollinated orchid Platanthera bifolia was studied. A significant decrease in scent production was detected both two and five days after pollination. The proportion of wilted flowers was higher in pollinated compared to control plants after seven days. A principal component analysis (PCA) showed how pollination reduced scent production. All scent compounds were affected by pollination, even though some compounds had larger impact on the overall scent reduction. A classification of samples offered a quantitative test of the changes found in individual plants after pollination. The induced decrease in floral scent production following pollination is suggested to be of adaptive value for both plants and pollinators.

Trends in floral scent chemistry in pollination syndromes: floral scent composition in moth-pollinated taxa

Floral scent from 15 moth-pollinated species in nine families was collected by head-space adsorption. The chemical composition was determined by coupled gas chromatography-mass spectrometry (GC-MS). The typical floral scent of moth-pollinated flowers contains some acyclic terpene alcohols, their corresponding hydrocarbons, benzenoid alcohols and esters and small amounts of some nitrogen compounds. The floral scent composition of sphingophilous flowers can be distinguished from that of phalaenophilous flowers by the presence of oxygenated sesquiterpenes. The flowers of three of the studied species had the general appearance and floral scent composition of moth-pollinated flowers, but contained no nectar reward. These species probably rely on deceptive pollination by naive visitors, which are deceived by the similarity of the flowers' morphological and scent chemistry to that of rewarding moth flowers. The finding of similar or structurally closely related floral scent compounds in both temperate and tropical species from both the Old and New worlds suggests that floral scent composition has been selected by a specific group of pollinators, moths that have similar sensory preferences. The functions of floral scent in moth-pollinated flowers are discussed in relation to an often observed over-representation of male moth visitors.

Trends in floral scent chemistry in pollination syndromes: floral scent composition in moth-pollinated taxa

Floral scent from 15 moth-pollinated species in nine families was collected by head-space adsorption. The chemical composition was determined by coupled gas chromatography-mass spectrometry (GC-MS). The typical floral scent of moth-pollinated flowers contains some acyclic terpene alcohols, their corresponding hydrocarbons, benzenoid alcohols and esters and small amounts of some nitrogen compounds. The floral scent composition of sphingophilous flowers can be distinguished from that of phalaenophilous flowers by the presence of oxygenated sesquiterpenes. The flowers of three of the studied species had the general appearance and floral scent composition of moth-pollinated flowers, but contained no nectar reward. These species probably rely on deceptive pollination by naive visitors, which are deceived by the similarity of the flowers' morphological and scent chemistry to that of rewarding moth flowers. The finding of similar or structurally closely related floral scent compounds in both temperate and tropical species from both the Old and New worlds suggests that floral scent composition has been selected by a specific group of pollinators, moths that have similar sensory preferences. The functions of floral scent in moth-pollinated flowers are discussed in relation to an often observed over-representation of male moth visitors.