GA as a regulatory link between the showy floral traits color and scent

Morphological and physiological investigations reveal the regulatory effect of exogenous paclobutrazol on flowering promotion by winter warming in Chaenomeles speciosa 'Changshouguan'

The application of exogenous paclobutrazol (PP333) can improve the ability of winter warming to promote flowering in Chaenomeles speciosa, but the underlying mechanism is unclear. In this study, the cultivar 'Changshouguan' was sprayed with different concentrations of PP333 during flower bud differentiation, and the changes in the anatomical structures and physiological characteristics of the flower buds during the differentiation process, as well as the growth state of the flower buds and the effect on flowering promotion after winter warming treatment, were comprehensively investigated. The results showed that different concentrations of PP333 could advance the flowering time of 'Changshouguan' by 15-24 d under the warming treatment and increase the flowering duration to 17 d compared with those under the warming treatment alone (CK), and 1000 mg/L was the best treatment. Compared with the CK treatment, the PP333 treatment decreased the contents of indole acetic acid (IAA) and gibberellic acid (GAs) and increased the contents of zeatin ribosides (ZRs) and abscisic acid (ABA), thus changing the balance of hormones during flower bud differentiation. The inflection point (low point) of the curve shapes of the ZRs/GAs and ZRs/IAA ratios appeared significantly earlier, which showed a pattern consistent with soluble sugar and protein content and antioxidant activity. Interestingly, the above changes also corresponded to earlier flowering times during the warming process. Taken together, these results indicate that spraying an appropriate concentration of PP333 in the early stage of 'Changshouguan' flower bud differentiation promotes the early differentiation of flower buds and early flowering under winter warming treatment by altering their endogenous hormone content and homeostasis and changing their physiological state. The key to maintaining a relatively long flowering period in plants in the PP333 treatment group after flowering promotion was the increased accumulation of sugars and proteins.

Research advances in regulation and genetic engineering of floral scents

Floral scents play important ecological roles because they attract pollinators and seed-dispersers. Historically, humans have used plant volatiles, including floral scents, as food additives, cosmetic products, and medicines. Floral scent formation and emissions are sometimes considerably affected by environmental and climatic conditions. Both enzymes and genes involved in floral scent biosynthesis have been consistently identified, and have provided insights into the potential of metabolic engineering of floral scents. This review summarizes recent studies on various aspects of floral scent biosynthesis and emission, including biosynthetic enzymes and genetic engineering. The findings ultimately show that the metabolic pathways of floral volatiles may be regulated by a more complex system than previously thought.

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.

The R2R3-MYB transcription factor EVER controls the emission of petunia floral volatiles by regulating epicuticular wax biosynthesis in the petal epidermis

The epidermal cells of petunia (Petunia × hybrida) flowers are the main site of volatile emission. However, the mechanisms underlying the release of volatiles into the environment are still being explored. Here, using cell-layer-specific transcriptomic analysis, reverse genetics by virus-induced gene silencing and clustered regularly interspaced short palindromic repeat (CRISPR), and metabolomics, we identified EPIDERMIS VOLATILE EMISSION REGULATOR (EVER)-a petal adaxial epidermis-specific MYB activator that affects the emission of volatiles. To generate ever knockout lines, we developed a viral-based CRISPR/Cas9 system for efficient gene editing in plants. These knockout lines, together with transient-suppression assays, revealed EVER's involvement in the repression of low-vapor-pressure volatiles. Internal pools and annotated scent-related genes involved in volatile production and emission were not affected by EVER. RNA-Seq analyses of petals of ever knockout lines and EVER-overexpressing flowers revealed enrichment in wax-related biosynthesis genes. Liquid chromatography/gas chromatography-MS analyses of petal epicuticular waxes revealed substantial reductions in wax loads in ever petals, particularly of monomers of fatty acids and wax esters. These results implicate EVER in the emission of volatiles by fine-tuning the composition of petal epicuticular waxes. We reveal a petunia MYB regulator that interlinks epicuticular wax composition and volatile emission, thus unraveling a regulatory layer in the scent-emission machinery in petunia flowers.

Chemistry, biosynthesis and biology of floral volatiles: roles in pollination and other functions

Covering: 2010 to 2023Floral volatiles are a chemically diverse group of plant metabolites that serve multiple functions. Their composition is shaped by environmental, ecological and evolutionary factors. This review will summarize recent advances in floral scent research from chemical, molecular and ecological perspectives. It will focus on the major chemical classes of floral volatiles, on notable new structures, and on recent discoveries regarding the biosynthesis and the regulation of volatile emission. Special attention will be devoted to the various functions of floral volatiles, not only as attractants for different types of pollinators, but also as defenses of flowers against enemies. We will also summarize recent findings on how floral volatiles are affected by abiotic stressors, such as increased temperatures and drought, and by other organisms, such as herbivores and flower-dwelling microbes. Finally, this review will indicate current research gaps, such as the very limited knowledge of the isomeric pattern of chiral compounds and its importance in interspecific interactions.

An integrated transcriptome and metabolome analysis reveals the gene network regulating flower development in Pogostemon cablin

Pogostemon cablin is a well-known protected species widely used in medicine and spices, however the underlying molecular mechanisms and metabolite dynamics of P. cablin flower development remain unclear due to the difficulty in achieving flowering in this species. A comparison of the transcriptome and widely targeted metabolome during P. cablin flower development was first performed in this study. Results showed that a total of 13,469 differentially expressed unigenes (DEGs) and 371 differentially accumulated metabolites (DAMs) were identified. Transcriptomic analysis revealed that the DEGs were associated with starch and sucrose metabolism, terpenoid biosynthesis and phenylpropanoid biosynthesis. Among these DEGs, 75 MIKC-MADS unigenes were associated with the development of floral organs. Gibberellins (GAs), auxin, and aging signaling might form a cross-regulatory network to regulate flower development in P. cablin. According to the metabolic profile, the predominant DAMs were amino acids, flavonoids, terpenes, phenols, and their derivatives. The accumulation patterns of these predominant DAMs were closely associated with the flower developmental stage. The integration analysis of DEGs and DAMs indicated that phenylpropanoids, flavonoids, and amino acids might be accumulated due to the activation of starch and sucrose metabolism. Our results provide some important insights for elucidating the reproductive process, floral organ, and color formation of P. cablin flowers at the molecular level. These results will improve our understanding of the molecular and genetic mechanisms involved in the floral development of P. cablin.

Developmental and temporal changes in petunia petal transcriptome reveal scent-repressing plant-specific RING-kinase-WD40 protein

In moth-pollinated petunias, production of floral volatiles initiates when the flower opens and occurs rhythmically during the day, for optimal flower-pollinator interaction. To characterize the developmental transcriptomic response to time of day, we generated RNA-Seq databases for corollas of floral buds and mature flowers in the morning and in the evening. Around 70% of transcripts accumulating in petals demonstrated significant changes in expression levels in response to the flowers' transition from a 4.5-cm bud to a flower 1 day postanthesis (1DPA). Overall, 44% of the petal transcripts were differentially expressed in the morning vs. evening. Morning/evening changes were affected by flower developmental stage, with a 2.5-fold larger transcriptomic response to daytime in 1DPA flowers compared to buds. Analyzed genes known to encode enzymes in volatile organic compound biosynthesis were upregulated in 1DPA flowers vs. buds-in parallel with the activation of scent production. Based on analysis of global changes in the petal transcriptome, PhWD2 was identified as a putative scent-related factor. PhWD2 is a protein that is uniquely present in plants and has a three-domain structure: RING-kinase-WD40. Suppression of PhWD2 (termed UPPER - Unique Plant PhEnylpropanoid Regulator) resulted in a significant increase in the levels of volatiles emitted from and accumulated in internal pools, suggesting that it is a negative regulator of petunia floral scent production.

SCARECROW-like GRAS protein PES positively regulates petunia floral scent production

Emission of scent volatiles by flowers is important for successful pollination and consequently, reproduction. Petunia (Petunia hybrida) floral scent is formed mainly by volatile products of the phenylpropanoid pathway. We identified and characterized a regulator of petunia scent production: the GRAS protein PHENYLPROPANOID EMISSION-REGULATING SCARECROW-LIKE (PES). Its expression increased in petals during bud development and was highest in open flowers. Overexpression of PES increased the production of floral volatiles, while its suppression resulted in scent reduction. We showed that PES upregulates the expression of genes encoding enzymes of the phenylpropanoid and shikimate pathways in petals, and of the core regulator of volatile biosynthesis ODORANT1 by activating its promoter. PES is an ortholog of Arabidopsis (Arabidopsis thaliana) PHYTOCHROME A SIGNAL TRANSDUCTION 1, involved in physiological responses to far-red (FR) light. Analyses of the effect of nonphotosynthetic irradiation (low-intensity FR light) on petunia floral volatiles revealed FR light as a scent-activating factor. While PHYTOCHROME A regulated scent-related gene expression and floral scent production under FR light, the influence of PES on volatile production was not limited by FR light conditions.

Microplastics and Nanoplastics Effects on Plant-Pollinator Interaction and Pollination Biology

Microplastics and nanoplastics (MNPs) contamination is an emerging environmental and public health concern, and these particles have been reported both in aquatic and terrestrial ecosystems. Recent studies have expanded our understanding of the adverse effects of MNPs pollution on human, terrestrial, and aquatic animals, insects, and plants. In this perspective, we describe the adverse effects of MNPs particles on pollinator and plant health and discuss the mechanisms by which MNPs disrupt the pollination process. We discuss the evidence and integrate transcriptome studies to investigate the negative effects of MNPs on the molecular biology of pollination, which may cause delay or inhibit the pollination services. We conclude by addressing challenges to plant-pollinator health from MNPs pollution and argue that such harmful effects disrupt the communication between plant and pollinator for a successful pollination process.

Transcriptome analysis identifies key gene LiMYB305 involved in monoterpene biosynthesis in Lilium 'Siberia'

Lilium is a popular cut flower that is highly favored by consumers due to its snowy white color and strong fragrance, which originates from the release of monoterpenes. However, the underlying molecular mechanism of monoterpene synthesis remains poorly understood. In this study, the content of three main monoterpenes (linalool, ocimene, and myrcene) was examined in Lilium 'Siberia', and RNA sequencing of the 11 stages of flower development was conducted. The biosynthesis of the three monoterpenes increased with flower development, reaching their peak levels at the full flowering stage. Transcriptome data revealed 257,140 unigenes, with an average size of 794 bp, from which 43,934 differentially expressed genes were identified and enriched in the KEGG pathways partly involved in plant hormone signal transduction and monoterpenoid biosynthesis. Furthermore, the essential factor LiMYB305 was identified by WGCNA after the release of the flower fragrance. The transient silencing of LiMYB305 in petals using VIGS technology showed that the mRNA expression levels of LiLiS, LiOcS, and LiMyS were significantly downregulated and that the release of linalool, ocimene, and myrcene had decreased significantly. Y1H, LUC, and EMSA experiments revealed that LiMYB305 directly bound and activated the LiOcS promoter to increase the synthesis of monoterpenes. Taken together, these results provide insight into the molecular mechanism of monoterpene synthesis and provide valuable information to investigate the formation of the flower fragrance in Lilium.

A whiff of the future: functions of phenylalanine-derived aroma compounds and advances in their industrial production

Plants produce myriad aroma compounds-odorous molecules that are key factors in countless aspects of the plant's life cycle, including pollinator attraction and communication within and between plants. For humans, aroma compounds convey accurate information on food type, and are vital for assessing the environment. The phenylpropanoid pathway is the origin of notable aroma compounds, such as raspberry ketone and vanillin. In the last decade, great strides have been made in elucidating this pathway with the identification of numerous aroma-related biosynthetic enzymes and factors regulating metabolic shunts. These scientific achievements, together with public acknowledgment of aroma compounds' medicinal benefits and growing consumer demand for natural products, are driving the development of novel biological sources for wide-scale, eco-friendly, and inexpensive production. Microbes and plants that are readily amenable to metabolic engineering are garnering attention as suitable platforms for achieving this goal. In this review, we discuss the importance of aroma compounds from the perspectives of humans, pollinators and plant-plant interactions. Focusing on vanillin and raspberry ketone, which are of high interest to the industry, we present key knowledge on the biosynthesis and regulation of phenylalanine-derived aroma compounds, describe advances in the adoption of microbes and plants as platforms for their production, and propose routes for improvement.

Genetic and Biochemical Aspects of Floral Scents in Roses

Floral scents possess high ornamental and economic values to rose production in the floricultural industry. In the past two decades, molecular bases of floral scent production have been studied in the rose as well as their genetic inheritance. Some significant achievements have been acquired, such as the comprehensive rose genome and the finding of a novel geraniol synthase in plants. In this review, we summarize the composition of floral scents in modern roses, focusing on the recent advances in the molecular mechanisms of floral scent production and emission, as well as the latest developments in molecular breeding and metabolic engineering of rose scents. It could provide useful information for both studying and improving the floral scent production in the rose.

Abscisic acid mediates the reduction of petunia flower size at elevated temperatures due to reduced cell division

Elevated temperatures suppress cell division in developing petunia buds leading to smaller flowers, mediated by ABA. Flower size is one of the most important showy traits in determining pollinator attraction, and a central factor determining the quality of floricultural products. Whereas the adverse effects of elevated temperatures on showy traits have been described in detail, its underlining mechanisms is poorly understood. Here, we investigated the physiological mechanism responsible for the reduction of flower size in petunia under elevated temperatures. We found that the early stages of flower-bud development were most sensitive to elevated temperatures, resulting in a drastic reduction of flower diameter that was almost independent of flower load. We demonstrated that the temperature-mediated flower size reduction occurred due to a shorter growth period, and a lower rate of corolla cell division. Consistently, local application of cytokinin, a phytohormone that promotes cell division, resulted in recovery of flower dimensions when grown under elevated temperatures. Hormone analysis of temperature-inhibited flower buds revealed no significant changes in levels of cytokinin, and a specific increase of abscisic acid (ABA) levels, known to inhibit cell division. Moreover, local application of ABA on flower buds caused a reduction of flower dimensions as a result of lower levels of cell division, suggesting that ABA mediates the reduction of flower size at elevated temperatures. Taken together, our results shed light on the mechanism by which elevated temperatures decrease petunia flower size, and show that temperature-mediated reduction of flower size can be alleviated by increasing the cytokinin/ABA ratio.

Spatial patterning of scent in petunia corolla is discriminated by bees and involves the ABCG1 transporter

Floral guides are patterned cues that direct the pollinator to the plant reproductive organs. The spatial distribution of showy visual and olfactory traits allows efficient plant-pollinator interactions. Data on the mechanisms underlying floral volatile patterns or their interactions with pollinators are lacking. Here we characterize the spatial emission patterns of volatiles from the corolla of the model plant Petunia × hybrida and reveal the ability of honeybees to distinguish these patterns. Along the adaxial epidermis, in correlation with cell density, the petal base adjacent to reproductive organs emitted significantly higher levels of volatiles than the distal petal rim. Volatile emission could also be differentiated between the two epidermal surfaces: emission from the adaxial side was significantly higher than that from the abaxial side. Similar emission patterns were also observed in other petunias, Dianthus caryophyllus (carnation) and Argyranthemum frutescens (Marguerite daisy). Analyses of transcripts involved in volatile production/emission revealed lower levels of the plasma-membrane transporter ABCG1 in the abaxial versus adaxial epidermis. Transient overexpression of ABCG1 enhanced emission from the abaxial epidermis to the level of the adaxial epidermis, suggesting its involvement in spatial emission patterns in the epidermal layers. Proboscis extension response experiments showed that differences in emission levels along the adaxial epidermis, that is, petal base versus rim, detected by GC-MS are also discernible by honeybees.

Dynamic histone acetylation in floral volatile synthesis and emission in petunia flowers

Biosynthesis of secondary metabolites relies on primary metabolic pathways to provide precursors, energy, and cofactors, thus requiring coordinated regulation of primary and secondary metabolic networks. However, to date, it remains largely unknown how this coordination is achieved. Using Petunia hybrida flowers, which emit high levels of phenylpropanoid/benzenoid volatile organic compounds (VOCs), we uncovered genome-wide dynamic deposition of histone H3 lysine 9 acetylation (H3K9ac) during anthesis as an underlying mechanism to coordinate primary and secondary metabolic networks. The observed epigenome reprogramming is accompanied by transcriptional activation at gene loci involved in primary metabolic pathways that provide precursor phenylalanine, as well as secondary metabolic pathways to produce volatile compounds. We also observed transcriptional repression among genes involved in alternative phenylpropanoid branches that compete for metabolic precursors. We show that GNAT family histone acetyltransferase(s) (HATs) are required for the expression of genes involved in VOC biosynthesis and emission, by using chemical inhibitors of HATs, and by knocking down a specific HAT gene, ELP3, through transient RNAi. Together, our study supports that regulatory mechanisms at chromatin level may play an essential role in activating primary and secondary metabolic pathways to regulate VOC synthesis in petunia flowers.

Gibberellins are required for dimorphic flower development in Viola philippica

Photoperiod is a major determinant of chasmogamous (CH)-cleistogamous (CL) dimorphic flower development in Viola philippica, and only long-day (LD) conditions induce CL flowers. In this study, it was found that the active gibberellin (GA) content in CL floral buds was higher than in CH floral buds formed under short-day (SD) conditions, suggesting that the biosynthesis of active GAs is enhanced by a longer photoperiod and may be associated with dimorphic flower development. Thus, the next step was to molecularly characterize the key V. philippica GA synthesis genes GA 20-oxidase (VpGA20ox) and GA 3-oxidase (VpGA3ox). In terms of the expression of VpGA20ox and VpGA3ox, it was found that the active GAs could be upregulated in developing pistils under both LD and SD conditions to develop functional pistils, and GAs could also accumulate in the stamens under SD conditions. The anthers and the adjacent petals were well developed under SD conditions. In contrast, the above-mentioned floral organs displayed low GA contents under LD conditions and were poorly developed. Although the application of paclobutrazol, an inhibitor of GA synthesis, did not reverse CL development under LD conditions, exogenous GAs could partially trigger the transition from CH to CL flowers under relative SD conditions (≤12 h daylight). This was coupled with the downregulation of B-class MADS-box genes, thereby restraining stamen and petal development. Both VpGA20ox and VpGA3ox exhibited similar expression profiles with B-class MADS-box genes in the development of the stamens and petals. Therefore, in response to photoperiod, GA signaling could affect the expression of B-class homeotic genes and regulate dimorphic flower development in Viola. As a compensation for poorly-developed nectaries, anthers, and petals, filament elongation, style shortness, and inward bending could ensure self-pollination in CL flowers. This work provides new insights into the regulation of CH-CL floral development and the evolutionary significance of the formation of dimorphic flowers.

Sugar and Hormone Dynamics and the Expression Profiles of SUT/SUC and SWEET Sweet Sugar Transporters during Flower Development in Petunia axillaris

Flowering is the first committed step of plant sexual reproduction. While the developing flower is a strong sink requiring large quantity of sugars from photosynthetic source tissues, this process is under-temper-spatially controlled via hormone signaling pathway and nutrient availability. Sugar transporters SUT/SUC and SWEET mediate sugars movement across membranes and play a significant role in various physiological processes, including reproductive organ development. In Petunia axillaris, a model ornamental plant, 5 SUT/SUC and 36 SWEET genes are identified in the current version of the genome. Analysis of their gene structure and chromosomal locations reveal that SWEET family is moderately expanded. Most of the transporter genes are abundantly expressed in the flower than in other organs. During the five flower developmental stages, transcript levels of PaSUT1, PaSUT3, PaSWEET13c, PaSWEET9a, PaSWEET1d, PaSWEET5a and PaSWEET14a increase with the maturation of the flower and reach their maximum in the fully open flowers. PaSWEET9c, the nectar-specific PhNEC1 orthologous, is expressed in matured and fully opened flowers. Moreover, determination of sugar concentrations and phytohormone dynamics in flowers at the five developmental stages shows that glucose is the predominant form of sugar in young flowers at the early stage but depletes at the later stage, whereas sucrose accumulates only in maturated flowers prior to the corolla opening. On the other hand, GA₃ content and to a less extent IAA and zeatin decreases with the flower development; however, JA, SA and ABA display a remarkable peak at mid- or later flower developmental stage.

Transcriptome analysis of Petunia axillaris flowers reveals genes involved in morphological differentiation and metabolite transport

The biosynthesis of plant secondary metabolites is associated with morphological and metabolic differentiation. As a consequence, gene expression profiles can change drastically, and primary and secondary metabolites, including intermediate and end-products, move dynamically within and between cells. However, little is known about the molecular mechanisms underlying differentiation and transport mechanisms. In this study, we performed a transcriptome analysis of Petunia axillaris subsp. parodii, which produces various volatiles in its corolla limbs and emits metabolites to attract pollinators. RNA-sequencing from leaves, buds, and limbs identified 53,243 unigenes. Analysis of differentially expressed genes, combined with gene ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses, showed that many biological processes were highly enriched in limbs. These included catabolic processes and signaling pathways of hormones, such as gibberellins, and metabolic pathways, including phenylpropanoids and fatty acids. Moreover, we identified five transporter genes that showed high expression in limbs, and we performed spatiotemporal expression analyses and homology searches to infer their putative functions. Our systematic analysis provides comprehensive transcriptomic information regarding morphological differentiation and metabolite transport in the Petunia flower and lays the foundation for establishing the specific mechanisms that control secondary metabolite biosynthesis in plants.

Two-dimensional analysis provides molecular insight into flower scent of Lilium 'Siberia'

Lily is a popular flower around the world not only because of its elegant appearance, but also due to its appealing scent. Little is known about the regulation of the volatile compound biosynthesis in lily flower scent. Here, we conducted an approach combining two-dimensional analysis and weighted gene co-expression network analysis (WGCNA) to explore candidate genes regulating flower scent production. In the approach, changes of flower volatile emissions and corresponding gene expression profiles at four flower developmental stages and four circadian times were both captured by GC-MS and RNA-seq methods. By overlapping differentially-expressed genes (DEGs) that responded to flower scent changes in flower development and circadian rhythm, 3,426 DEGs were initially identified to be candidates for flower scent production, of which 1,270 were predicted as transcriptional factors (TFs). The DEGs were further correlated to individual flower volatiles by WGCNA. Finally, 37, 41 and 90 genes were identified as candidate TFs likely regulating terpenoids, phenylpropanoids and fatty acid derivatives productions, respectively. Moreover, by WGCNA several genes related to auxin, gibberellins and ABC transporter were revealed to be responsible for flower scent production. Thus, this strategy provides an important foundation for future studies on the molecular mechanisms involved in floral scent production.

Phenylpropanoid Scent Compounds in Petunia x hybrida Are Glycosylated and Accumulate in Vacuoles

Floral scent has been studied extensively in the model plant Petunia. However, little is known about the intracellular fate of scent compounds. Here, we characterize the glycosylation of phenylpropanoid scent compounds in Petunia x hybrida. This modification reduces scent compounds' volatility, reactivity, and autotoxicity while increasing their water-solubility. Gas chromatography-mass spectrometry (GC-MS) analyses revealed that flowers of petunia cultivars accumulate substantial amounts of glycosylated scent compounds and that their increasing level parallels flower development. In contrast to the pool of accumulated aglycones, which drops considerably at the beginning of the light period, the collective pool of glycosides starts to increase at that time and does not decrease thereafter. The glycoside pool is dynamic and is generated or catabolized during peak scent emission, as inferred from phenylalanine isotope-feeding experiments. Using several approaches, we show that phenylpropanoid scent compounds are stored as glycosides in the vacuoles of petal cells: ectopic expression of Aspergillus niger β-glucosidase-1 targeted to the vacuole resulted in decreased glycoside accumulation; GC-MS analysis of intact vacuoles isolated from petal protoplasts revealed the presence of glycosylated scent compounds. Accumulation of glycosides in the vacuoles seems to be a common mechanism for phenylpropanoid metabolites.