Floral Scent Emission Research Articles

Aerial litter mimicry: A novel form of floral deception mediated by a monoterpene synthase

Abstract Floral mimics deceive their pollinators by developing visual and olfactory resemblance to various models. We report a flower that exhibits phenotypes like aerial litter and deceives an aerial litter specialist beetle to achieve pollination. We assessed the floral phenology and the effective pollinators of an Australian understorey treelet, Meiogyne heteropetala (Annonaceae). The similarities of morphology, colour and odour between the flowers and co‐occurring aerial litter were investigated. The terpene synthase involved in floral scent emission was identified by expression patterns and product profile. The behavioural responses of the pollinator to various odours were assessed using bioassays. The erotylid beetle Loberus sharpi is the most likely effective pollinator because it was the only pollen‐laden visitor during the pistillate phase. Loberus sharpi was exclusively found in aerial litter and M. heteropetala flowers. The flowers offer an honest shelter reward. The beetle also oviposits there, but most larvae eventually perished as the petals dropped onto the forest floor. The morphology and spectral reflectance of the flowers overlap with aerial litter. The floral scent was dominated by monoterpenes, especially 1,8‐cineole. The cineole synthase MhCINS was the only highly expressed floral terpene synthase and possessed a highly similar product profile to the floral scent composition. The volatile composition of M. heteropetala flowers is distinct from other congeners and highly similar to aerial litter, indicating advergence to aerial litter. Visual and odour resemblance, coupled with low larval survivorship, provides evidence that the beetles were deceived into pollinating the flowers. Behavioural experiments showed that the pollinator was attracted to both aerial litter and M. heteropetala flowers. The beetles were also attracted to 1,8‐cineole and synthetic mixes of floral odour and MhCINS products. The beetles were unable to distinguish floral scent from MhCINS products nor from 1,8‐cineole, suggesting MhCINS alone sufficed to attract the pollinator olfactorily. The beetles, however, preferred aerial litter over flowers. The beetles likely categorised the flower as a general, but not the most preferred, brood substrate. Synthesis. This study reports the first case of floral mimicry of aerial litter and characterises the biochemical process responsible for olfactory mimicry.

Evidence for diurnal bee pollination in the ancestrally hawkmoth-pollinated genus Crinum (Amaryllidaceae)

Abstract Shifts between diurnal and nocturnal pollination systems have been important in the radiation of the angiosperms. Here we examined the pollination ecology of Crinum campanulatum (Amaryllidaceae), an aquatic geophyte. Although visits by noctuid moths were observed in the evening, the flowers of C. campanulatum were visited mainly by honeybees and carpenter bees. The species was found to be self-incompatible, and flowers exposed to only diurnal visitors produced a higher number of fruits and seeds than those exposed to only nocturnal visitors. Overall seed production was not pollen limited. The floral scent was found to be dominated by aromatic compounds, including many with functional groups containing nitrogen. The chemical composition of scent did not differ between day and night samples, but floral scent emissions during the day were ~8-fold greater than those at night. Flower colour changes from white to a dark pink over four days from anthesis, which is associated with increased conspicuousness to bees. Ancestral state reconstruction revealed that long-tubed flowers pollinated by hawkmoths are ancestral and widespread in Crinum. These results are indicative of a shift from nocturnal to diurnal pollination in Crinum that is associated with a reduction in flower size and an increase in diurnal scent emission.

Petunia PHYTOCHROME INTERACTING FACTOR 4/5 transcriptionally activates key regulators of floral scent

Floral scent emission of petunia flowers is regulated by light conditions, circadian rhythms, ambient temperature and the phytohormones GA and ethylene, but the mechanisms underlying sensitivity to these factors remain obscure. PHYTOCHROME INTERACTING FACTORs (PIFs) have been well studied as components of the regulatory machinery for numerous physiological processes. Acting redundantly, they serve as transmitters of light, circadian, metabolic, thermal and hormonal signals. Here we identified and characterized the phylogenetics of petunia PIF family members (PhPIFs). PhPIF4/5 was revealed as a positive regulator of floral scent: TRV-based transient suppression of PhPIF4/5 in petunia petals reduced emission of volatiles, whereas transient overexpression increased scent emission. The mechanism of PhPIF4/5-mediated regulation of volatile production includes activation of the expression of genes encoding biosynthetic enzymes and a key positive regulator of the pathway, EMISSION OF BENZENOIDS II (EOBII). The PIF-binding motif on the EOBII promoter (G-box) was shown to be needed for this activation. As PhPIF4/5 homologues are sensors of dawn and expression of EOBII also peaks at dawn, the prior is proposed to be part of the diurnal control of the volatile biosynthetic machinery. PhPIF4/5 was also found to transcriptionally activate PhDELLAs; a similar positive effect of PIFs on DELLA expression was further confirmed in Arabidopsis seedlings. The PhPIF4/5–PhDELLAs feedback is proposed to fine-tune GA signaling for regulation of floral scent production.

Floral scent and pollination of the invasive plant Coreopsis lanceolata in Japan

The invasive plant Coreopsis lanceolata threatens ecosystems in Japan by competing for resources with native plants. This species is self-incompatible and requires pollinator agents for seed production; however, it is known to produce many seeds. Here, we document the pollination biology and plant-pollinator interactions that facilitate seed production of C. lanceolata in the introduced range. Results revealed that C. lanceolata attracted a wide array of floral visitors comprising 60 species from 20 families. Although most floral visitors could be potential pollinators, the functional groups of halictid bees appeared to be the most important pollinators of C. lanceolata in terms of visitation frequency and the ability to carry pollen. The floral scent emission of C. lanceolata consists predominantly of monoterpenes, sesquiterpenes, and benzenoids. Furthermore, the mean seed set was nearly 30% of the ovule mean. Our study confirmed that in the introduced range in Japan, C. lanceolata is integrated into the local pollinator community, especially with the functional group of halictid bees involved in the reproductive success.

Floral Scents in Bee-Pollinated Buckwheat and Oilseed Rape under a Global Warming Scenario.

Many wild plants and crops are pollinated by insects, which often use floral scents to locate their host plants. The production and emission of floral scents are temperature-dependent; however, little is known about how global warming affects scent emissions and the attraction of pollinators. We used a combination of chemical analytical and electrophysiological approaches to quantify the influence of a global warming scenario (+5 °C in this century) on the floral scent emissions of two important crop species, i.e., buckwheat (Fagopyrum esculentum) and oilseed rape (Brassica napus), and to test whether compounds that are potentially different between the treatments can be detected by their bee pollinators (Apis mellifera and Bombus terrestris). We found that only buckwheat was affected by increased temperatures. Independent of temperature, the scent of oilseed rape was dominated by p-anisaldehyde and linalool, with no differences in relative scent composition and the total amount of scent. Buckwheat emitted 2.4 ng of scent per flower and hour at optimal temperatures, dominated by 2- and 3-methylbutanoic acid (46%) and linalool (10%), and at warmer temperatures threefold less scent (0.7 ng/flower/hour), with increased contributions of 2- and 3-methylbutanoic acid (73%) to the total scent and linalool and other compounds being absent. The antennae of the pollinators responded to various buckwheat floral scent compounds, among them compounds that disappeared at increased temperatures or were affected in their (relative) amounts. Our results highlight that increased temperatures differentially affect floral scent emissions of crop plants and that, in buckwheat, the temperature-induced changes in floral scent emissions affect the olfactory perception of the flowers by bees. Future studies should test whether these differences in olfactory perception translate into different attractiveness of buckwheat flowers to bees.

PbABCG1 and PbABCG2 transporters are required for the emission of floral monoterpenes in Phalaenopsis bellina.

Terrestrial plants emit volatiles into the atmosphere to attract both pollinators and the enemies of herbivores, for defense. Phalaenopsis bellina is a scented orchid species in which the main scent components are monoterpenes, including linalool and geraniol, and their derivatives. Here, we investigated whether ABC transporters are involved in floral scent emission. We carried out whole-genome identification of ABC transporter-related genes using four floral transcriptomics libraries of P. bellina. We identified 86 ABC subfamily G genes related to terpenoid transport. After comparing the gene expression patterns of P. bellina with that of Phalaenopsis aphrodite subsp. formosana, a scentless species, followed by gene-to-gene correlation analysis, PbABCG1 and PbABCG2 were selected. The temporal expression of both PbABCG1 and PbABCG2 was highly correlated with that of the key enzyme PbGDPS and the major transcription factor PbbHLH4 in monoterpene biosynthesis, with optimal expression on day5 post-anthesis. Spatial gene expression analysis showed that PbABCG1 was highly expressed in sepals, whereas PbABCG2 was expressed in the lip. Subcellular localization with a GFP fusion protein revealed that both PbABCG1 and PbABCG2 are cytoplasmic membrane proteins. Co-downregulation of PbABCG1 and PbABCG2 using both double-strand RNA interference and tobacco rattle virus-based gene silencing led to a significant decrease in monoterpene emission, accompanied by an increase in the internal monoterpene pools. Furthermore, ectopic expression of PbABCG1 and PbABCG2 in an ABC16- mutant yeast strain rescued its tolerance to geraniol. Altogether, our results indicate that PbABCG1 and PbABCG2 play substantial roles in monoterpene transport/emission in P. bellina floral scent.

Water Deficit, Nitrogen Availability, and Their Combination Differently Affect Floral Scent Emission in Three Brassicaceae Species

Floral scent plays a central role in plant-pollinator interactions, as flower visitors can discriminate between scent differences to recognize and forage on rewarding flowers. Changes in scent compositions might therefore lead to recognition mismatches between host plants and flower visitors. An understanding of the phenotypic plasticity of floral scent, especially in crop species, is becoming important because of climate change, e.g., increasing drought periods, and other anthropogenic influences, e.g., nitrogen (N) deposition. We have investigated the effects of the combination of progressive water deficits (dry-down) and N supplementation on floral scent emission in three Brassicaceae species (cultivated vs. wild). Individuals were randomly assigned to one of four treatments: (1) well-watered without N supplementation; (2) well-watered with N supplementation; (3) dry-down without N supplementation; (4) dry-down with N supplementation. We collected scent on day 0, 2, 7, and 14 after the commencement of the watering treatment. All samples were analyzed using gas chromatography coupled with mass spectrometry. We found that the highly cultivated Brassica napus had the lowest overall emission rate; its scent composition was affected by the interaction of watering treatment and N supplementation. Scent bouquets of the cultivated Sinapis alba also changed under these treatments. Scent bouquets of the common weed Sinapis arvensis were affected by watering treatment, but not by time and N supplementation. Furthermore, the influence of treatments on the emission rate of single compounds was highly compound-specific. Nonetheless, our study revealed that especially terpenes were negatively affected by drought-stress.

Do onion (Allium cepa L.) floral scent emissions peak when pollinators are most active?

Do onion (Allium cepa L.) floral scent emissions peak when pollinators are most active?

Population-specific responses of floral volatiles to abiotic factors in changing environments.

Shifts in abiotic factors can affect many plant traits, including floral volatiles. This study examined the response of floral volatiles to water availability and whether phenotypic plasticity to water availability differs among populations. It also investigated genetic differentiation in floral volatiles, determined the effect of temperature on phenotypic plasticity to water availability, and assessed temporal variation in floral scent emission between day and evening, since pollinator visitation differs at those times. Rocky Mountain columbine plants (Aquilegia coerulea), started from seeds collected in three wild populations in Colorado, Utah, and Arizona, were grown under two water treatments in a greenhouse in Madison, Wisconsin, United States. One population was also grown under the two water treatments, at two temperatures. Air samples were collected from enclosed flowers using dynamic headspace methods and floral volatiles were identified and quantified by gas chromatography (GC) with mass spectrometry (MS). Emission of three floral volatiles increased in the wetter environment, indicating phenotypic plasticity. The response of six floral volatiles to water availability differed among populations, suggesting genetic differentiation in phenotypic plasticity. Five floral volatiles varied among populations, and emission of most floral volatiles was greater during the day. Phenotypic plasticity to water availability permits a quick response of floral volatiles in changing environments. The genetic differentiation in phenotypic plasticity suggests that phenotypic plasticity can evolve but complicates predictions of the effects of environmental changes on a plant and its pollinators.

Real-Time Visualization of Scent Accumulation Reveals the Frequency of Floral Scent Emissions.

Flowers emit a bouquet of volatiles to attract pollinators or to protect flowers from pathogen and herbivore attacks. Most floral volatiles are synthesized in the cytoplasm of petals and released into the headspace at a specific time of day. Various floral scent sampling methods coupled with gas chromatography-mass spectrometry have been used to measure the quality and quantity of floral volatiles. However, little is known about the emission patterns of floral scents. In most cases, it is still unclear whether floral scents emit continuously or discontinuously. Here we measured the frequency with which lily flowers emit scents using optical interferometry. By analyzing the refractive index difference between volatile organic compounds and ambient air, we were able to visualize the accumulation of the volatile vapors. The frequency of volatile emission was calculated from the unique footprint of temporal power spectrum maps. Based on these real-time measurements, we found that lily flowers emit the volatile compounds discontinuously, with pulses observed around every 10–50 min.

Extensive population-level sampling reveals clinal variation in (R)-(−)-linalool produced by the flowers of an endemic evening primrose, Oenothera harringtonii

The study of floral trait diversity has a long history due to its role in angiosperm diversification. While many studies have focused on visual traits including morphology and color, few have included floral scent despite its importance in pollination. Of the studies that have included floral scent, sampling has been limited and rarely explores variation at the population level. We studied geographic variation in the flowers of Oenothera harringtonii, a rare plant endemic to a vulnerable shortgrass prairie habitat, whose population structure and conservation status are well studied. The self-incompatible flowers of O. harringtonii open at dusk, produce nectar and a strong fragrance, and are pollinated by hawkmoths. We collected floral trait (morphology, scent chemistry and emission rates) data from 650 individuals from 19 wild populations to survey floral variation across the entire range of this species. Similarly, we collected floral data from 49 individuals grown in a greenhouse common garden, to assess whether variation observed in the field is consistent when environment factors (temperature, watering regime, soil) are standardized. We identified 35 floral volatiles representing 5 biosynthetic classes. Population differentiation was stronger for floral scent chemistry than floral morphology. (R)-(−)-linalool was the most important floral trait differentiating populations, exhibiting clinal variation across the distribution of O. harringtonii without any correlated shifts in floral morphology. Populations in the north and west produced (R)-(−)-linalool consistently, those in the east and south largely lacked it, and populations at the center of the distribution were polymorphic. Floral scent emissions in wild populations varied across four years but chemical composition was largely consistent over time. Similarly, volatile emission rates and chemical composition in greenhouse-grown plants were consistent with those of wild populations of origin. Our data set, which represents the most extensive population-level survey of floral scent to date, indicates that such sampling may be needed to capture potentially adaptive geographic variation in wild populations.

The Similarity of Floral Scent Composition in Two Breynia Species Pollinated by the Same Host-Specific Epicephala Moth

Floral scent has been thought to play a critical role in the obligate pollination–seed consumption mutualism between Breynia (Phyllanthaceae) species and Epicephala moths. The two closely related Breynia species, B. fruticosa and B. Rostrata are jointly pollinated by the same moth species (E. lativalvaris and E. mirivalvata), which has led to an obligate pollination mutualism of ‘two-to-two’ species specificity. However, empirical data on host floral volatiles as chemical cues maintaining the plant−moth specificity are missing. In the present study, 27 volatile compounds were identified from floral scents of the two Breynia species. A total of 25 compounds were shared jointly by the two species, and only one compound, β-humulene, was species specific and exclusively produced by B. fruticosa. The two Breynia species clearly showed no interspecific floral scent profiles within both sexes, especially in male flowers. Male and female flowers of floral scent from these plants exhibited major qualitative differences, and male flowers produced more scent than female flowers. For male flowers of B. fruticosa, there was significant temporal variation in the volatile chemical profiles and total floral scent emission before and after pollination. Interestingly, β-phenylethyl butyrate and phenylethyl alcohol were present in maximal amounts during pollination, but they rapidly reduced in concentration after pollination. The findings suggest that the similar floral scent profiles of the two Breynia species reflect adaptations to the same pollinator, Epicephala, for their pollination. Sexually dimorphic floral scent between male and female flowers has been selected to provoke pollinator’s active pollination behavior on host flowers. Temporal changes in floral scent of male flowers before and after pollination may have evolved to limit the overexploitation of the ovaries by seed predators, Epicephala moths. We speculate that the two most abundant compounds in the male flowers, β-phenylethyl butyrate and phenylethyl alcohol, may be two signal compounds to attract Epicephala in a species-specific manner.

Nocturnal emission and post‐pollination change of floral scent in the leafflower tree, Glochidion rubrum, exclusively pollinated by seed‐parasitic leafflower moths

AbstractMany insect‐pollinated plants use floral scent signals to attract and guide the effective pollinators, and temporal patterns of their floral scent emission may be tuned to respond to the pollinator's activity and pollination status. In the intimate nursery pollination mutualism between monoecious Glochidion trees (Phyllanthaceae) and Epicephala moths (Gracillariidae), floral scent signals mediate species‐specific interactions and influence the moth's efficient pollen‐collecting and pollen‐depositing behaviors on male and female flowers, respectively. We tested the hypotheses that both sexes of flowers of Epicephala‐pollinated Glochidion rubrum exhibit a diel pattern of scent emission matching the activity period of the nocturnally active pollinator, and that female flowers change the chemical signal after pollination to reduce further visits and oviposition by the pollinator. We investigated the diel change of floral scent emissions during two consecutive days and the influence of pollination on the floral scent by conducting hand‐pollinations in the field. The total scent emission of male and female flowers was higher at night than in the day, which would be expected from the nocturnal visitations of Epicephala moths. Some compounds exhibited a clear nocturnal emission rhythm. Hand‐pollination experiments revealed that emission of two compounds, nerolidol and eugenol, drastically decreased in pollinated flowers, suggesting that these compounds may function as key attractants for the pollinator; however, the total scent emission of the female flower was not influenced by hand‐pollination. The pattern of the floral scent emission of G. rubrum may be optimized to attract nocturnal pollinators and reduce oviposition.

Phenotypic plasticity in floral scent in response to nutrient, but not water, availability in the perennial plant Arabis alpina

Abstract Floral scent is an important mediator of plant–pollinator interactions. Multiple recent studies report ample intraspecific scent variation among populations and individuals. Yet, few studies have estimated effects of phenotypic plasticity on floral scent in response to differing environmental factors. In this study, we investigated the effects of nutrient and water availability on floral scent in self‐compatible and self‐incompatible populations of the perennial herb Arabis alpina. We subjected greenhouse grown plants to different nutrient and water treatments in a crossed design, examined the effects on floral scent emission rate and composition, compared the level of plasticity to that of other plant traits, and conducted hand‐pollinations of nutrient‐limited individuals to test for a potential allocation cost of scent production. For both self‐compatible and self‐incompatible populations, the per‐flower scent emission rate was 1.2–4 times higher when nutrients were abundant, but this effect explained little variation in scent emission rate and was limited compared to plasticity in flower number. There was no effect of water treatment on scent emission. Additionally, neither treatment had an effect on the composition of the floral scent, and there was no detectable trade‐off between scent and seed production that would imply a cost of floral scent production. Overall, while per‐flower floral scent emission displayed limited phenotypic plasticity in response to nutrient conditions, the total amount of scent emitted by plants may increase more strongly at higher nutrient availabilities due to an increase in flower production. Therefore, our results suggest that fitness benefits due to increased scent emission rates under favourable nutrient conditions might depend on the extent to which floral scent serves as a long‐ or short‐distance pollinator attractant for the focal plant species. A free Plain Language Summary can be found within the Supporting Information of this article.

Pollination ecology and floral scent chemistry of Philodendron fragrantissimum (Araceae)

ABSTRACT In French Guiana, Philodendron fragrantissimum (Hook.) G.Don was specifically pollinated by a single species of night-active cyclocephaline scarab, Cyclocephala simulatrix Höhne. Its inflorescences exhibited short-lasting anthesis (~30 h) and characteristic floral traits such as floral thermogenesis, edible/nutritious floral tissues, and profuse floral scent emission. Our insect exclusion experiments indicate that entomophilous cross-pollination is obligatory for P. fragrantissimum, with olfactory signalling playing a pivotal role in pollinator attraction. Three volatile organic compounds – methyl benzoate, (Z)-jasmone, and dehydrojasmone – dominate the floral scent of pistillate phase inflorescences (84–99%), but their relative proportions were different according to the headspace sampling method used, dynamic or static. Local pollination services provided by both female and male C. simulatrix are effective, as evidenced by a high visitation rate (>70%) that resulted in 55% of the inflorescences maturing into infructescences. Moreover, pollination was highly efficient, since 2–3 beetles sufficed to pollinate an average 94% of the pistillate flowers.

GcProfileMakeR: An R Package for Automatic Classification of Constitutive and Non-Constitutive Metabolites.

Metabolomes comprise constitutive and non-constitutive metabolites produced due to physiological, genetic or environmental effects. However, finding constitutive metabolites and non-constitutive metabolites in large datasets is technically challenging. We developed gcProfileMakeR, an R package using standard Excel output files from an Agilent Chemstation GC-MS for automatic data analysis using CAS numbers. gcProfileMakeR has two filters for data preprocessing removing contaminants and low-quality peaks. The first function NormalizeWithinFiles, samples assigning retention times to CAS. The second function NormalizeBetweenFiles, reaches a consensus between files where compounds in close retention times are grouped together. The third function getGroups, establishes what is considered as Constitutive Profile, Non-constitutive by Frequency i.e., not present in all samples and Non-constitutive by Quality. Results can be plotted with the plotGroup function. We used it to analyse floral scent emissions in four snapdragon genotypes. These included a wild type, Deficiens nicotianoides and compacta affecting floral identity and RNAi:AmLHY targeting a circadian clock gene. We identified differences in scent constitutive and non-constitutive profiles as well as in timing of emission. gcProfileMakeR is a very useful tool to define constitutive and non-constitutive scent profiles. It also allows to analyse genotypes and circadian datasets to identify differing metabolites.

Genome-wide identification and expression pattern of SnRK gene family under several hormone treatments and its role in floral scent emission in Hedychium coronarium.

The SnRK (Snf1-Related protein Kinase) gene family plays crucial roles in various plant signaling pathways and stress-adaptive responses including biotic and abiotic stresses via activating protein phosphorylation pathways. However, there is no information available on the role of the SnRK gene family in Hedychium coronarium. H. coronarium is an important crop widely cultivated as an ornamental plant, herb, spice, or condiment. In this study, 60 HcSnRK genes were identified from the H. coronarium genomic and transcriptome data. Phylogenetic and gene structure analysis showed that the HcSnRK genes were divided into three groups (HcSnRK1, HcSnRK2 and HcSnRK3) and among them HcSnRK3 subfamily was further subdivided into two clades according to the number of introns. Chromosome localization analysis showed that HcSnRK genes were unevenly mapped onto all chromosomes, and the Ka/Ks ratio of 24 paralogues includes four tandems and 20 segmental duplications indicated that the HcSnRK gene family underwent a purifying selection. Cis-regulatory elements analysis suggested that the HcSnRK genes respond to multiple hormones and other stresses. The responsiveness of HcSnRK genes to several hormones was analyzed by quantitative real-time PCR. Based on the different transcriptome data, two candidates HcSnRK genes (HcSnRK2.2 and HcSnRK2.9) were screened out for further characterization . The subcellular localization experiment revealed that both genes were located in the nucleus and cytoplasm. Moreover, virus-induced gene silencing (VIGS) of HcSnRK2.2 and HcSnRK2.9 significantly reduced the floral volatile contents by suppressing the expression of terpene synthase genes (HcTPS1, HcTPS3, and HcTPS5), indicating that HcSnRK2.2 and HcSnRK2.9 genes play an important role in the regulatory mechanism of floral aroma. These results will provide novel insights into the functional dissection of H. coronarium SnRK gene family.

Evolution of floral scent in relation to self-incompatibility and capacity for autonomous self-pollination in the perennial herb Arabis alpina.

Background and AimsThe transition from outcrossing to selfing is a frequent evolutionary shift in flowering plants and is predicted to result in reduced allocation to pollinator attraction if plants can self-pollinate autonomously. The evolution of selfing is associated with reduced visual floral signalling in many systems, but effects on floral scent have received less attention. We compared multiple populations of the arctic–alpine herb Arabis alpina (Brassicaceae), and asked whether the transition from self-incompatibility to self-compatibility has been associated with reduced visual and chemical floral signalling. We further examined whether floral signalling differ between self-compatible populations with low and high capacity for autonomous self-pollination, as would be expected if benefits of signalling decrease with reduced dependence on pollinators for pollen transfer.MethodsIn a common garden we documented flower size and floral scent emission rate and composition in eight self-compatible and nine self-incompatible A. alpina populations. These included self-compatible Scandinavian populations with high capacity for autonomous self-pollination, self-compatible populations with low capacity for autonomous self-pollination from France and Spain, and self-incompatible populations from Italy and Greece.Key ResultsThe self-compatible populations produced smaller and less scented flowers than the self-incompatible populations. However, flower size and scent emission rate did not differ between self-compatible populations with high and low capacity for autonomous self-pollination. Floral scent composition differed between self-compatible and self-incompatible populations, but also varied substantially among populations within the two categories.ConclusionsOur study demonstrates extensive variation in floral scent among populations of a geographically widespread species. Contrary to expectation, floral signalling did not differ between self-compatible populations with high and low capacity for autonomous self-pollination, indicating that dependence on pollinator attraction can only partly explain variation in floral signalling. Additional variation may reflect adaptation to other aspects of local environments, genetic drift, or a combination of these processes.

Scent emissions and expression of scent emission-related genes: A comparison between cut and intact carnation flowers

Although the physiological states of intact and cut flowers are expected to be significantly different, the floral scent emissions of these two conditions has yet to be compared. We compared the scent emissions from intact and cut flowers using carnation (Dianthus caryophyllus L.) cultivars with two different scent-types—a fruity scent based on benzenoid methyl benzoate and a spicy scent based on eugenol. Methyl benzoate or eugenol, which were the principal scent components, always had the highest percentage (> 30 %) in both intact and cut flowers from flower opening to wilting. The total emissions from intact flowers remained at a similar level for approximately 6 days after flower opening, and then gradually decreased with flower senescence. The total emissions from cut flowers were highest on the day of flower opening and then decreased more rapidly than emissions from intact flowers. Furthermore, the duration of noticeable scent of cut flowers was estimated to be shorter than that of intact flowers. The expression of various scent emission-related genes encoding floral volatile benzenoid/phenylpropanoid biosynthesis enzymes, adenosine triphosphate-binding cassette transporters, and MYB transcription factors increased with flower opening and were accompanied by scent emissions. However, the expressions of most of these genes were not affected by cutting, suggesting that the decrease in scent emissions from cut flowers is unlikely due to changes in gene expression. Recently, we reported that cutting accelerates the decrease in sugar content and increases ethylene production in carnation petals, resulting in hastened flower senescence. Therefore, the rapid decrease in scent emissions from cut flowers may be due to a decrease in sugars, which are substrates for the scent components.

Bumblebee Behavior on Flowers, but Not Initial Attraction, Is Altered by Short-Term Drought Stress.

Climate change is leading to increasing drought and higher temperatures, both of which reduce soil water levels and consequently water availability for plants. This reduction often induces physiological stress in plants, which in turn can affect floral development and production inducing phenotypic alterations in flowers. Because flower visitors notice and respond to small differences in floral phenotypes, changes in trait expression can alter trait-mediated flower visitor behavior. Temperature is also known to affect floral scent emission and foraging behavior and, therefore, might modulate trait-mediated flower visitor behavior. However, the link between changes in flower visitor behavior and floral traits in the context of increasing drought and temperature is still not fully understood. In a wind-tunnel experiment, we tested the behavior of 66 Bombus terrestris individuals in response to watered and drought-stressed Sinapis arvensis plants and determined whether these responses were modulated by air temperature. Further, we explored whether floral traits and drought treatment were correlated with bumblebee behavior. The initial attractiveness of drought and watered plants did not differ, as the time to first visit was similar. However, bumblebees visited watered plants more often, their visitation rate to flowers was higher on watered plants, and bumblebees stayed for longer, indicating that watered plants were more attractive for foraging. Bumblebee behavior differed between floral trait expressions, mostly independently of treatment, with larger inflorescences and flowers leading to a decrease in the time until the first flower visit and an increase in the number of visits and the flower visitation rate. Temperature modulated bumblebee activity, which was highest at 25°C; the interaction of drought/water treatment and temperature led to higher visitation rate on watered plants at 20°C, possibly as a result of higher nectar production. Thus, bumblebee behavior is influenced by the watered status of plants, and bumblebees can recognize differences in intraspecific phenotypes involving morphological traits and scent emission, despite overall morphological traits and scent emission not being clearly separated between treatments. Our results indicate that plants are able to buffer floral trait expressions against short-term drought events, potentially to maintain pollinator attraction.