Emission Of Floral Volatiles Research Articles

Impacts of ramet density and herbivory on floral volatile emissions and seed production in Solidago altissima.

Plants produce an array of floral olfactory and visual cues to attract pollinators, including volatile organic compounds (VOC), which mediate plant-pollinator interactions and may be influenced by herbivory and neighboring plants. Consequently, these factors may affect plant fitness by disrupting pollination. However, most evidence comes from controlled experiments, limiting our understanding of how VOCs function in natural populations. This study investigated how herbivory and conspecific ramet density influence floral VOC profile, pollination, and seed production in a naturally occurring population of Solidago altissima. We recorded leaf herbivory and ramet density surrounding one focal ramet in 1-m2 plots. We collected VOCs from the floral headspace and measured ovary fertilization as a proxy for pollination success and the number of seeds produced by the focal ramet. Our findings revealed interactive effects between ramet density and herbivory on floral VOC emission, richness, and diversity. Specifically, at lower ramet densities, herbivory did not affect floral volatile emissions. However, in highly dense stands, herbivory suppressed floral volatile emissions. Despite these changes, floral volatiles did not affect pollination and the number of seeds in S. altissima. Our field-based findings underscore the importance of understanding the complex responses of floral VOCs to environmental stressors and their contributions to plant reproduction within natural communities. Our results suggest that while herbivory and ramet density influence floral scent, these changes do not affect reproduction in our study. Ultimately, generalist-pollinated plants like S. altissima might not rely heavily on chemical signaling during pollination.

Natural selection on floral volatiles and other traits can change with snowmelt timing and summer precipitation.

Climate change is disrupting floral traits that mediate mutualistic and antagonistic species interactions. Plastic responses of these traits to multiple shifting conditions may be adaptive, depending on natural selection in new environments. We manipulated snowmelt date over three seasons (3-11 d earlier) in factorial combination with growing-season precipitation (normal, halved, or doubled) to measure plastic responses of volatile emissions and other floral traits in Ipomopsis aggregata. We quantified how precipitation and early snowmelt affected selection on traits by seed predators and pollinators. Within years, floral emissions did not respond to precipitation treatments but shifted with snowmelt treatment depending on the year. Across 3 yr, emissions correlated with both precipitation and snowmelt date. These effects were driven by changes in soil moisture. Selection on several traits changed with earlier snowmelt or reduced precipitation, in some cases driven by predispersal seed predation. Floral trait plasticity was not generally adaptive. Floral volatile emissions shifted in the face of two effects of climate change, and the new environments modulated selection imposed by interacting species. The complexity of the responses underscores the need for more studies of how climate change will affect floral volatiles and other floral traits.

Diurnal patterns of floral volatile emissions in three species of Narcissus.

Plants generate a wide array of signals such as olfactory cues to attract and manipulate the response of pollinators. The present study addresses the temporal patterns of scent emission as an additional dimension to the scent composition. The expectation is that divergent floral function is reflected in divergent qualitative and temporal emission patterns. We used GC-ion mobility spectrometry with an integrated pre-concentration for automated acquisition of the temporal trends in floral volatile emissions for N. viridiflorus, N. papyraceus, and N. cantabricus subsp. foliosus. We found a considerable increase in scent emissions and changes in scent composition for N. viridiflorus at night. This increase was particularly pronounced for aromatic substances such as benzyl acetate and p-cresol. We found no diurnal patterns in N. papyraceus, despite a similar qualitative composition of floral volatiles. Narcissus cantabricus subsp. foliosus showed no diurnal patterns either and differed considerably in floral scent composition. Scent composition, circadian emission patterns, and floral morphology indicate divergent, but partially overlapping pollinator communities. However, the limited pollinator data from the field only permits a tentative correlation between emission patterns and flower visitors. Narcissus papyraceus and N. cantabricus show no clear diurnal patterns and thus no adjustment to the activity patterns of their diurnal pollinators. In N. viridiflorus, timing of scent emission indicates an adaptation to nocturnal flower visitors, contradicting Macroglossum as the only reported pollinator. We propose that the legitimate pollinators of N. viridiflorus are nocturnal and are still unidentified.

Temporal, Developmental, and Comparative Characterization of the Floral Volatile Emissions of the Famously Scented Violet Species, Viola odorata

Violets (Viola) are potential candidates for aroma-focused breeding research. Though most Viola species and modern hybrids lack fragrance, the genus contains a famously scented species, Viola odorata L. This species and its cultivars are genetic resources of aroma traits that could be used to investigate the selection for and transmission of fragrance during the breeding process. Despite its famous scent, however, the floral volatile emissions of V. odorata have not been characterized using modern headspace techniques. Using static and dynamic headspace volatile collection methods and gas chromatography–mass spectrometry, the floral volatile emissions of V. odorata were temporally and developmentally characterized. Floral volatiles were also sampled from 10 V. odorata cultivars, three Parma violet cultivars, five violet species, and one hybrid, and variation in scent among these violets was investigated. Total volatile emissions in V. odorata were highest from 0600 HR to 1900 HR, suggesting a diurnal pattern of emission. Volatile emissions also varied over the developmental lifespan of the flower, with the highest emission of individual and total volatiles occurring, in general, from stages 0 or +1 to stages +3 or +4. Floral scent qualitatively and quantitatively differed among assorted violets. The floral volatile emissions of V. odorata exhibit temporal and developmental variation. Compared with the other violet species in this study, sweet violets are intensely fragrant. The quantity and quality of floral scent differs among V. odorata cultivars, providing genetic variation from which selections could be made in a fragrance-focused breeding program.

Effects of experimental warming on floral scent, display, and rewards in two subalpine herbs.

Floral volatiles, visual traits, and rewards mediate attraction and defense in plant-pollinator and plant-herbivore interactions, but these floral traits may be altered by global warming through direct effects of temperature or longer term impacts on plant resources. We examined the effect of warming on floral and leaf volatile emissions, floral morphology, plant height, nectar production, and oviposition by seed predators. We used open-top chambers that warmed plants in the field +2-3 °C on average (+6-11 °C increase in daily maxima) for 2-4 weeks across 1-3 years at 3 sites in Colorado, USA. Volatiles were sampled from two closely related species of subalpine Ipomopsis with different pollinators: I. aggregata ssp. aggregata, visited mainly by hummingbirds, and I. tenuituba ssp. tenuituba, often visited by hawkmoths. While warming had no detected effects on leaf volatiles, the daytime floral volatiles of both I. aggregata and I. tenuituba responded in subtle ways to warming, with impacts that depended on the species, site, and year. In addition to the long-term effect of warming, temperature at the time of sampling independently affected the floral volatile emissions of I. aggregata during the day and I. tenuituba at night. Warming had little effect on floral morphology for either species, and no effect on nectar concentration, maximum inflorescence height, or flower redness in I. aggregata. However, warming increased nectar production in I. aggregata by 41%, a response that would attract more hummingbird visits, and reduced oviposition by fly seed predators by at least 72%. Our results suggest that floral traits can show different levels of plasticity to temperature changes in subalpine environments, with potential effects on animal behaviors that help or hinder plant reproduction. They also illustrate the need for more long-term field warming studies, as shown by responses of floral volatiles in different ways to weeks of warming versus temperature at the time of sampling.

Insect herbivory but not plant pathogen infection drive floral volatile‐mediated indirect effects on pollinators and plant fitness in Brassica rapa

Abstract Plant enemies can indirectly affect pollinators by modifying plant traits, but simultaneous tests of herbivore and pathogen effects are lacking, and the role of floral volatiles has seldom been assessed. In this study, we tested for indirect effects of insect herbivores and pathogens on pollinator attraction via altered floral volatile emissions, and its consequences for plant fitness in Brassica rapa. Plants in the field were exposed to either no damage or damage by caterpillars (Mamestra brassicae), aphids (Brevicoryne brassicae), a leaf fungus (Sclerotinia sclerotiorum), or a bacterium (Xanthomonas campestris pv. campestris). We then recorded pollinator visits and measured floral traits (flower number, volatiles) and plant fitness‐correlates. We additionally performed a greenhouse experiment with artificial floral emitters to test for effects of target volatiles on pollinator attraction. In the field experiments, relative to controls, plants subjected to herbivory by the aphid B. brassicae (but not those exposed to the other enemies) exhibited a marked reduction in the emission of two volatile organic compounds (nonanal and 2‐butyl‐1‐octanol), experienced lower pollinator visits and produced seeds of lower quality in terms of seed biomass and germination rate, while flower output itself was not affected. Consistently, artificial emitters with reduced amounts of these volatile organic compounds were less attractive to pollinators under greenhouse conditions. Synthesis. These results provide strong evidence for volatile‐mediated indirect interactions between plant enemies and pollinators ultimately impacting plant fitness, and further point at enemy and compound specificity in such effects.

Bumblebee responses to variation in pollinator-attracting traits of Vicia faba flowers.

Adaptations that attract pollinators to flowers are central to the reproductive success of insect-pollinated plants, including crops. Understanding the influence of these non-rewarding traits on pollinator preference is important for our future food security by maintaining sufficient crop pollination. We have identified substantial variation in flower shape, petal size, corolla-tube length, petal spot size and floral volatile compounds among a panel of 30 genetically distinct lines of Vicia faba. Using this variation, we found that Bombus terrestris was able to distinguish between natural variation in petal spot size, floral volatile emissions and corolla-tube length. Foragers showed some innate preference for spotted flowers over non-spotted flowers and preferred shorter corolla-tube lengths over longer tubes. Our results suggest that some floral traits may have significant potential to enhance pollinator attraction to V. faba crops, particularly if paired with optimised rewards.

Fungicides and strawberry pollination-Effects on floral scent, pollen attributes and bumblebee behavior.

Fungicides are used in agriculture to protect crops from various fungal diseases. However, they may modulate the plants metabolism. Moreover, fungicides can accumulate in the environment and may cause toxic effects on non-target organisms such as nectar microbes and pollinators. Nectar microbes contribute to the volatile profile of flowers and can influence pollinators behaviour. Thus, fungicide treatment could potentially affect the pollination. In this study, we investigated the influence of fungicide treatment on floral attributes as well as the behavioural impact on bumblebees. In separate experiments, we used one or both strawberry cultivars (Fragaria × ananassa var. Darselect and Malwina), which were either kept untreated (control) or treated with either Cuprozin® progress or SWITCH® fungicide. We analysed various flower traits including volatiles, pollen weight, pollen protein, and the attraction of bumblebees towards the flowers in the greenhouse. Additionally, we analysed the viability of pollen and pollen live-to-dead ratio, as well as the composition of nectar fungi in the field. A treatment with Cuprozin® progress led to a lower emission of floral volatiles and a slightly lower pollen protein content. This had no impact on the visit latency of bumblebees but on the overall visit frequency of these flowers. The treatment with the fungicide SWITCH® resulted in a higher emission of floral volatiles as well as a delayed first visit by bumblebees. Furthermore, flowers of control plants were visited more often than those treated with the two fungicides. Plant-pollinator interactions are highly complex, with many contributing factors. Fungicides can have an impact on the pollen quality and pollinator attraction, potentially leading to an altered pollen dispersal by pollinators and a change in fruit quality.

Supplemental far-red light influences flowering traits and interactions with a pollinator in tomato crops

Plants sense a reduction in the red to far-red light ratio as a cue of light competition and respond by accelerated growth and reproduction. These responses can be exploited in horticulture by applying far-red light-emitting diodes (LEDs). Responses to far-red light also have marked effects on plant defences and influence plant-herbivore and plant-carnivore interactions. It is, however, not known how changes in flowering traits induced by far-red light affect plant-pollinator interactions. We studied the effects of supplemental far-red light on tomato truss development, floral volatiles, pollen sugar and amino acid content, and the foraging behaviour of the buff-tailed bumblebee (Bombus terrestris).Far-red light significantly increased plant height, accelerated flowering and increased the number of flowers per truss. Floral volatile emission was increased in the early stages of tomato development, and sugar content was higher in pollen of plants exposed to far-red light. Pollen amino acid content was not affected. Bumblebees spent more time foraging on far-red-exposed plants and visited more flowers on these plants.We conclude that plant exposure to far-red light leads to changes in flower traits that increase the attraction of bumblebees, which has promising implications for the use of supplemental far-red LEDs in greenhouse tomato crops.

Emission of floral volatiles is facilitated by cell-wall non-specific lipid transfer proteins

For volatile organic compounds (VOCs) to be released from the plant cell into the atmosphere, they have to cross the plasma membrane, the cell wall, and the cuticle. However, how these hydrophobic compounds cross the hydrophilic cell wall is largely unknown. Using biochemical and reverse-genetic approaches combined with mathematical simulation, we show that cell-wall localized non-specific lipid transfer proteins (nsLTPs) facilitate VOC emission. Out of three highly expressed nsLTPs in petunia petals, which emit high levels of phenylpropanoid/benzenoid compounds, only PhnsLTP3 contributes to the VOC export across the cell wall to the cuticle. A decrease in PhnsLTP3 expression reduces volatile emission and leads to VOC redistribution with less VOCs reaching the cuticle without affecting their total pools. This intracellular build-up of VOCs lowers their biosynthesis by feedback downregulation of phenylalanine precursor supply to prevent self-intoxication. Overall, these results demonstrate that nsLTPs are intrinsic members of the VOC emission network, which facilitate VOC diffusion across the cell wall.

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.

Zn2+ induces changes in activities of mitochondrial respiratory chain complexes and emissions of floral volatiles in Dendrobium huoshanense

Abstract In recent years, there has been increasing interest in floral volatiles due to their important function in reproduction, self-protection and so on. Although some progress was made on deciphering emissions of floral volatiles and on related mechanisms under a variety of environmental factors, the effects of Zn2+ concentrations on mitochondrial function and floral volatile emissions are yet to be revealed. Dendrobium huoshanense petals were used as materials and were treated with a 0–8 mM ZnSO4 solution. Intracellular Zn2+ concentrations were evaluated by the fluorescent dye method and atomic absorption method. Mitochondrial respiratory chain complex activities and the precursor and ATP contents were determined by the biochemical method. Floral volatile components were analyzed by the gas chromatograph-mass spectrometer (GC-MS). The results indicated that ZnSO4 application significantly increased intracellular Zn2+ concentrations. Elevated intracellular Zn2+ concentrations differently affected mitochondrial respiratory chain complex activities, precursor and adenosine triphosphate (ATP) productions and floral volatile emissions. Moreover, positive correlations exist among the activities of mitochondrial respiratory chain complexes, productions of precursors and ATP and emissions of floral volatiles. It is concluded that Zn2+ concentrations induce the activity changes of mitochondrial respiratory chain complexes, especially complex II and V, which promote or inhibit the emissions of floral volatiles by affecting the precursor and ATP levels that are closely related to the production of terpenoids, benzoids and fatty acid derivatives. The research will contribute to understanding the relationship between Zn2+ concentrations and floral volatile emissions from the perspective of mitochondrial function.

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.

Dynamic regulation of volatile terpenoid production and emission from Chrysanthemum morifolium capitula

Flower-associated communities consist of both mutualistic and antagonistic organisms. We have limited knowledge on how flowers regulate volatiles to balance their defense against antagonists and the attraction of beneficial organisms necessary for reproductive success. Asteraceae is the largest family among flowering plants. Its representatives are characterized by unique inflorescence called capitulum, which has been reduced to a reproduction unit resembling a single flower. Here, we chose Chrysanthemum morifolium, a model species of Asteraceae, to investigate how the capitulum balances the accumulation and emission of floral terpenoid volatiles that are implicated in defense and pollinator attraction, respectively. Our results showed that the capitula of C. morifolium produce and emit complex mixtures of monoterpenoids and sesquiterpenoids. The highest concentrations of terpenoids were detected in the bud stage of the capitula. In contrast, the capitulum reached the highest emission level prior to full blooming. The disc florets were the dominant organs of terpenoid accumulation and emission in the full-openness stage. To understand the molecular basis of volatile terpenoid biosynthesis in C. morifolium, experiments were designed to study terpene synthase (TPS) genes, which are pivotal for terpene biosynthesis. Eight CmCJTPS genes were identified in the transcriptomes of C. morifolium, and the proteins encoded by five genes were found to be biochemically functional. CmCJTPS5 and CmCJTPS8 were the multi-product enzymes catalyzing the monoterpenoid and sesquiterpenoid formation, which closely matched the major terpenoids produced in the flower heads. The five functional terpene synthase genes exhibited similar temporal expression patterns but diverse spatial expression levels, suggesting tissue-specific functions. Altogether, our results illustrate the dynamic patterns of accumulation and emission of floral volatile terpenoids implicated in defense and attracting pollinators in C. morifolium, for which both the regulation of TPS gene expression and the regulation of release may play critical roles.

Floral traits differentiate pollination syndromes and species but fail to predict the identity of floral visitors to Castilleja.

Animal pollination is critical to plant reproduction and may cause convergent evolution of pollination syndromes. Pollination syndromes in Castilleja have been distinguished based on floral traits and historical observations of floral visitors. Here we addressed these questions: (1) Can pollination syndromes be distinguished using floral morphological traits or volatile organic compound emissions? (2) Is there significant variation in floral traits within a pollination syndrome at the level of populations or species? (3) Do pollination syndromes predict the most frequent floral visitor to Castilleja? Floral traits and visitation were measured for five co-occurring Castilleja species (C. applegatei, C. linariifolia, C. miniata, C. nana, and C. peirsonii), representing three pollination syndromes (bee, fly, and hummingbird), at four sites in the Sierra Nevada Mountains. We used nonmetric multidimensional scaling (NMDS) and multiple linear regressions to address key questions in the differentiation of Castilleja and floral visitors. Our analyses revealed that both morphological traits and floral VOCs can be used to distinguish between some pollination syndromes and Castilleja species. Morphological traits defined pollination syndromes reliably, but within the hummingbird syndrome, there was also significant variation among populations and species. Pollination syndrome was a poor predictor of visitors to Castilleja. Floral trait differentiation among Castilleja individuals reflects both taxonomy and pollination syndromes. Differentiation was generally more evident in morphological traits compared to VOCs. Furthermore, a priori notions of pollination syndromes in this system are overly simplistic and fail to predict which animals most frequently visit Castilleja in natural populations.

Differences in Floral Scent and Petal Reflectance Between Diploid and Tetraploid Chamerion angustifolium

Genome duplication in plants is thought to be a route to speciation due to cytotype incompatibility. However, to reduce cross-pollination between cytotypes in animal-pollinated species, distinctive floral phenotypes, which would allow pollinator-mediated assortative mating between flowers, are also expected. Chamerion angustifolium is a Holarctic species that forms a hybrid zone between diploid and tetraploid populations in the North American Rocky Mountains. Extensive research has shown that these cytotypes differ in many ways, including some floral traits, and that pollinators can discriminate between cytotypes, leading to assortative mating. However, two signals commonly used by insect pollinators have not been measured for this species, namely petal colour and floral scent. Using greenhouse-grown diploids and tetraploids of C. angustifolium from the ploidy hybrid-zone in the North American Rocky Mountains, we show that both floral scent signals and petal reflectance differ between cytotypes. These differences, along with differences in flower size shown previously, could help explain pollinator-mediated assortative mating observed in previous studies. However, these differences in floral phenotypes may vary in importance to pollinators. While the differences in scent included common floral volatiles readily detected by bumblebees, the differences in petal reflectance may not be perceived by bees based on their visual sensitivity across the spectra. Thus, our results suggest that differences in floral volatile emissions are more likely to contribute to pollinator discrimination between cytotypes and highlight the importance of understanding the sensory systems of pollinators when examining floral signals.

Bumblebee electric charge stimulates floral volatile emissions in Petunia integrifolia but not in Antirrhinum majus

The timing of volatile organic compound (VOC) emission by flowering plants often coincides with pollinator foraging activity. Volatile emission is often considered to be paced by environmental variables, such as light intensity, and/or by circadian rhythmicity. The question arises as to what extent pollinators themselves provide information about their presence, in keeping with their long co-evolution with flowering plants. Bumblebees are electrically charged and provide electrical stimulation when visiting plants, as measured via the depolarisation of electric potential in the stem of flowers. Here we test the hypothesis that the electric charge of foraging bumblebees increases the floral volatile emissions of bee pollinated plants. We investigate the change in VOC emissions of two bee-pollinated plants (Petunia integrifolia and Antirrhinum majus) exposed to the electric charge typical of foraging bumblebees. P. integrifolia slightly increases its emissions of a behaviorally and physiologically active compound in response to visits by foraging bumblebees, presenting on average 121 pC of electric charge. We show that for P. integrifolia, strong electrical stimulation (600–700 pC) promotes increased volatile emissions, but this is not found when using weaker electrical charges more representative of flying pollinators (100 pC). Floral volatile emissions of A. majus were not affected by either strong (600–700 pC) or weak electric charges (100 pC). This study opens a new area of research whereby the electrical charge of flying insects may provide information to plants on the presence and phenology of their pollinators. As a form of electroreception, this sensory process would bear adaptive value, enabling plants to better ensure that their attractive chemical messages are released when a potential recipient is present.

Biosynthesis and emission of methyl hexanoate, the major constituent of floral scent of a night-blooming water lily Victoriacruziana

Among the factors that have made flowering plants the most species-rich lineage of land plants is the interaction between flower and insect pollinators, for which floral scent plays a pivotal role. Water lilies belong to the ANA (Amborellales, Nymphaeales, and Austrobaileyales) grade of basal flowering plants. In this study, Victoria cruziana was investigated as a model night-blooming water lily for floral scent biosynthesis. Four volatile compounds, including three benzenoids and one fatty acid methyl ester methyl hexanoate, were detected from the flowers of V. cruziana during their first bloom, with methyl hexanoate accounting for 45 % of total floral volatile emission. Emission rates were largely constant before significant drop starting at the end of second bloom. To understand the molecular basis of floral scent biosynthesis in V. cruziana, particularly methyl hexanoate, a transcriptome from the whole flowers at the full-bloom stage was created and analyzed. Methyl hexanoate was hypothesized to be biosynthesized by SABATH methyltransferases. From the transcriptome, three full-length SABATH genes designated VcSABATH1-3 were identified. A full-length cDNA for each of the three VcSABATH genes was expressed in Escherichia coli to produce recombinant proteins. When tested in in vitro methyltransferase enzyme assays with different fatty acids, both VcSABATH1 and VcSABATH3 exhibited highest levels of activity with hexanoic acid to produce methyl hexanoate, with the specific activity of VcSABATH1 being about 15 % of that for VcSABATH3. VcSABATH1 and VcSABATH3 showed the highest levels of expression in stamen and pistil, respectively. In phylogenetic analysis, three VcSABATH genes clustered with other water lily SABATH methyltransferase genes including the one known for making other fatty acid methyl esters, implying both a common evolutionary origin and functional divergence. Fatty acid methyl esters are not frequent constituents of floral scents of mesangiosperms, pointing to the importance for the evolution of novel fatty acid methyltransferase for making fatty acid methyl esters in the pollination biology of water lilies.

Revealing floral metabolite network in tuberose that underpins scent volatiles synthesis, storage and emission.

The role of central carbon metabolism in the synthesis and emission of scent volatiles in tuberose flowers was revealed through measurement of changes in transcripts and metabolites levels. Tuberose or Agave amica (Medikus) Thiede & Govaerts is a widely cultivated ornamental plant in several subtropical countries. Little is known about metabolite networking involved in biosynthesis of specialized metabolites utilizing primary metabolites. In this study, metabolite profiling and gene expression analyses were carried out from six stages of maturation throughout floral lifespan. Multivariate analysis indicated distinction between early and late maturation stages. Further, the roles of sugars viz. sucrose, glucose and fructose in synthesis, glycosylation and emission of floral scent volatiles were studied. Transcript levels of an ABC G family transporter (picked up from the floral transcriptome) was in synchronization with terpene volatiles emission during the anthesis stage. A diversion from phenylpropanoid/benzenoid to flavonoid metabolism was observed as flowers mature. Further, it was suggested that this metabolic shift could be mediated by isoforms of 4-Coumarate-CoA ligase along with Myb308 transcription factor. Maximum glycosylation of floral scent volatiles was shown to occur at the late mature stage when emission declined, facilitating both storage and export from the floral tissues. Thus, this study provides an insight into floral scent volatiles synthesis, storage and emission by measuring changes at transcripts and metabolites levels in tuberose throughout floral lifespan.

Concentration-dependent emission of floral scent terpenoids from diverse cultivars of Chrysanthemum morifolium and their wild relatives

Floral scent is an important trait that has a significant influence on the reproduction of many flowering plants and the market value of several ornamental crops. The family of Asteraceae is well known for its unique floral structure (capitulum) that consists of many florets. Although the constituents of either floral essential oils or emitted floral volatiles have been reported in many species of Asteraceae, little information is available on the mechanisms that determine floral volatile emission. In the present study, a total of 44 species/varieties of Chrysanthemum were analyzed to determine the relationship between the internal accumulation of floral terpenoids and their release as volatiles. By performing both headspace collection and organic extraction, it has been found that the emission rates of floral terpenoids are largely correlated to their internal concentrations. Particularly, the flowers of cultivated C. morifolium, when compared to their wild relatives, were found to exhibit lower emission rates that contain lowered concentrations of floral terpenoids. The differences were largely determined by six monoterpenes and five sesquiterpenes that were revealed by principal component analysis. Besides, the relationship between concentrations and emission rates of floral terpenoids as well as the sizes of capitulum was studied in detail. Separated into three different parts, disc florets were found to have a larger contribution to floral volatile emission than ray florets, whereas the phyllaries and receptacles are the main parts of volatiles accumulation. Finally, the potential biosynthetic pathway of the floral terpenoids produced in capitula of Chrysanthemum was proposed. In summary, our findings on the diversity and variations of floral terpenoids in Chrysanthemum reveal correlations between their production and emission. These findings can be useful to develop different plant breeding methods to create novel aromatic cultivars of Chrysanthemum.