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MAP  >  Ornamental Plant Research
2023 Volume 3
Article Contents
Abstract
Introduction
Origin and distribution, germplasm, and characteristics of M. cordata
Chemical resources and biological activities of M. cordata
Total synthesis, semi-synthesis, and structural modification of alkaloids in M. cordata
Total synthesis of major secondary metabolites in M. cordata
Semi-synthesis and structural modification of novel 6-substituted dihydrobenzo[c]phenanthridine alkaloids in M. cordata
Multi-omics analysis of the biosynthesis mechanism of sanguinarine in M. cordata
Discovery of the alkaloid biosynthesis pathway in M. cordata
Integrated analysis of genomics, transcriptomics, metabolomics, and proteomics in M. cordata to elucidate the mechanisms of sanguinarine storage, synthesis, and transport
Metabolic engineering for the biosynthesis of sanguinarine
Breeding research on M. cordata
Molecular breeding of M. cordata
Study on the domestication and DUS testing guidelines of M. cordata
The role of M. cordata in animal production and the mechanism and safety of sanguinarine as a feed antibiotic substitute
Future challenges and prospects
Author contributions
Data availability
Acknowledgments
Conflict of interest
Supplementary information
Rights and permissions
References
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ARTICLE   Open Access    

Analysis of fragrance compounds in flowers of Chrysanthemum genus

  • 1.

    Beijing Key Laboratory of Development and Quality Control of Ornamental Crops, Department of Ornamental Horticulture, China Agricultural University, Beijing 100193, China

  • 2.

    Institute of Agri-food Processing and Nutrition (IAPN), Beijing Academy of Agriculture and Forestry Sciences, Beijing 100089, China

  • # These authors contributed equally: Zhiling Wang, Xin Zhao

More Information
  • Chrysanthemum is one of the four major cut flowers in the world, with high ornamental and economic value. Fragrance is an important ornamental character of chrysanthemum flowers, especially those consumed as tea and other foods, and the flower fragrance is the major determinant of the commercial value of chrysanthemum cultivars. Currently, however, the research on chrysanthemum flower fragrance is mainly focused on the composition and content of fragrant compounds, and a clear classification of fragrance types is lacking. Here, we divided chrysanthemum fragrance into six categories based on sensory evaluation and determined the identity and content of fragrant compounds of chrysanthemum accessions representative of each fragrance type by GC-MS. In addition, we analyzed the conserved aromatic substances responsible for the fruity fragrance type chrysanthemum with multi-functional development potential, providing a theoretical basis for creating new chrysanthemum germplasm with specific fragrance types. The results of this study can accelerate the breeding process of chrysanthemum accessions with new fragrance types.

  • Introduction

    Macleaya cordata (Willd.) R. Br., commonly known as boluohui in China, is a perennial, upright herbaceous plant belonging to the Papaveraceae family (Fig. 1)[1]. Modern pharmacological research has identified that plants of the Macleaya genus are rich in benzylisoquinoline alkaloids (BIAs), which exhibit significant anti-inflammatory and antibacterial properties, regulate intestinal microflora, and promote animal growth[2]. The European Food Safety Authority (EFSA) has approved M. cordata as a safe plant for the manufacture of feed additives. In China, four alkaloids found in M. cordata, including sanguinarine (SAN), chelerythrine (CHE), allocryptopine (ALL), and protopine (PRO) have been successfully developed into veterinary medicines (Fig. 1).

    Figure 1.  Morphological characteristics of M. cordata. The figure shows various parts of M. cordata, commonly known as boluohui. The main image displays a field of mature plants with characteristic upright growth. The top left inset highlights a single leaf with a broad, lobed structure. The top middle inset shows the flower of M. cordata, featuring clustered blooms with delicate petals. The top right inset illustrates the capsule, the fruiting body containing seeds. These images collectively depict the key morphological features of M. cordata, which is valued for its rich content of benzylisoquinoline alkaloids.
    DownLoad: Full-Size Img PowerPoint

    This review aims to provide a comprehensive overview of the latest advancements in the study of M. cordata. It will cover the plant's resources, chemical composition, pharmacological activities, biosynthesis mechanisms, and breeding strategies. By synthesizing current knowledge, this review seeks to offer a broad perspective on future research and potential applications of M. cordata in various fields.

    Origin and distribution, germplasm, and characteristics of M. cordata

    The Macleaya genus comprises two species: M. cordata, and M. microcarpa. M. cordata is primarily distributed in China and Japan, originating in the regions south of the Yangtze River and north of the Nanling Mountains in China. It extends south to Guangdong, west to Guizhou, and northwest to southern Gansu. M. cordata predominantly grows in hills, low mountain forests, shrubs, or grasses at altitudes between 150 and 830 m. It is notably found in grasslands or shrubs on slopes at elevations ranging from 450 to 1,600 m in provinces such as Jiangsu, Jiangxi, Shanxi, Gansu, and Shaanxi.

    Both M. cordata, and M. microcarpa are upright herbaceous plants with a woody base, producing a milky yellow sap. Their stems are hollow, with the upper parts branching out, and the leaves are broad ovate or nearly circular. They possess large conical inflorescences that can be both terminal and axillary, with a flowering and fruiting period from June to November. Plants of the Macleaya genus are rich in various chemical constituents, including alkaloids, flavonoids, terpenes, and phenylpropanoids, with alkaloids being the predominant components[3]. Benzylisoquinoline alkaloids, such as sanguinarine, are among the most active components in this genus. Sanguinarine is also abundant in other plants like poppy (Papaver somniferum) and bloodroot (Sanguinaria canadensis); however, due to regulatory restrictions and over-exploitation, these plants are no longer viable sources. Consequently, M. cordata has emerged as the primary commercial source of sanguinarine.

    Chemical resources and biological activities of M. cordata

    Japanese researchers such as Tani & Takao[4] and Takao[5] isolated alkaloids like sanguinarine, chelerythrine, berberine, and coptisine from M. cordata, initiating the study of its chemical constituents. Subsequently, numerous researchers contributed to the isolation and structural identification of secondary metabolites in the Macleaya genus[6−9]. From 2009 to 2024, Qing et al.[10] developed a new method for the discovery and structural identification of alkaloids in the Macleaya genus using mass spectrometry, identifying over 200 alkaloids. These alkaloids belong to ten major categories: benzylisoquinoline alkaloids, tetrahydroprotoberberine alkaloids, N-methyl-tetrahydroprotoberberine alkaloids, protopine alkaloids, protoberberine alkaloids, 7,8-dihydroprotoberberine alkaloids, aporphine alkaloids, benzophenanthridine alkaloids, dihydrobenzophenanthridine alkaloids, and benzophenanthridine dimers (Fig. 2). Using mass spectrometry-guided techniques, over 20 new compounds were isolated from Macleaya species, established a mass spectrometry database and metabolic profile for alkaloids in Macleaya, and proposed new biosynthetic pathways for berberine and sanguinarine[10−13]. In addition to a large number of alkaloids, Macleaya species also contain small amounts of flavonoids and polyphenols[3]. The rich chemical composition of Macleaya endows it with various biological activities. Modern pharmacological studies have shown that Macleaya possesses antibacterial, anti-inflammatory, insecticidal, antitumor, antifibrotic, hepatoprotective, antiviral, antioxidant, immune-enhancing, gut microbiota-regulating, animal growth-promoting, wastewater-purifying, and soil erosion-preventing properties[13−16].

    Figure 2.  Types of compounds identified in Macleaya species.
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    Total synthesis, semi-synthesis, and structural modification of alkaloids in M. cordata

    Total synthesis of major secondary metabolites in M. cordata

    The primary active secondary metabolites in Macleaya cordata are protopine alkaloids and quaternary benzo[c]phenanthridine alkaloids. To date, there have been no reports in the literature regarding the total chemical synthesis of protopine alkaloids. The total chemical synthesis of quaternary benzo[c]phenanthridine alkaloids is generally achieved through multi-step reactions using conventional chemical reagents[17]. In most reported synthetic routes, the cyclization reactions to form rings B and C constitute the final steps in constructing the tetracyclic system. Key chemical reactions for constructing ring B include Heck coupling to form the C10a-C11 bond[18], Pictet-Spengler reaction (PS reaction) or Bischler-Napieralski reaction (BN reaction) to form the C6-C6a bond[19,20], amidation to form the N5-C6 bond[21], and electrocyclization to form the N5-C5a bond[22]. For ring C, key reactions include enamide-aldehyde cyclization to form the C11-C11a bond[23] and Friedel-Crafts reaction to form the C12-C12a bond[24]. These reactions have been widely applied in the synthesis of benzo[c]phenanthridine derivatives with anticancer activity (Fig. 3).

    Figure 3.  Total synthesis of quaternary benzo[c]phenanthridine alkaloids, the major active components of M. cordata. This figure illustrates the chemical structure of quaternary benzo[c]phenanthridine alkaloids, highlighting the tetracyclic framework composed of rings A, B, C, and D. These alkaloids are notable for their complex ring system and significant biological activities. The positions of the rings are labeled for clarity, facilitating understanding of the synthetic pathways and structural modifications discussed in the study.
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    Semi-synthesis and structural modification of novel 6-substituted dihydrobenzo[c]phenanthridine alkaloids in M. cordata

    In recent years, with the deepening research on the chemical constituents of M. cordata, a series of 6-substituted dihydrobenzo[c]phenanthridine alkaloids have been successively isolated and structurally confirmed (Fig. 4)[6,9,25,26]. Currently, studies on the biological activities of these alkaloids are still in their infancy, and no biosynthetic pathways for 6-substituted dihydrobenzo[c]phenanthridine alkaloids have been reported. Based on the structural types and chemical properties of the C-6 substituents, it is speculated that these alkaloids may be biosynthesized in plants through radical reactions or nucleophilic substitution pathways. As shown in Fig. 4, quaternary benzo[c]phenanthridine alkaloids or dihydrobenzo[c]phenanthridine can be converted to α-amino carbon radicals through single-electron reduction[27,28] or oxidation[29,30]. These radicals can then undergo various types of radical reactions to achieve functionalization at C-6 of the benzo[c]phenanthridine ring structure, resulting in the semi-synthesis of the aforementioned alkaloids[31]. Additionally, the N5=C6 double bond in quaternary benzo[c]phenanthridine alkaloids can accept nucleophilic reagents, leading to the formation of 6-substituted dihydrobenzo[c]phenanthridine alkaloids.

    Figure 4.  Novel 6-substituted dihydrobenzophenanthridine alkaloids in Macleaya and their semi-synthesis.
    DownLoad: Full-Size Img PowerPoint

    Multi-omics analysis of the biosynthesis mechanism of sanguinarine in M. cordata

    Discovery of the alkaloid biosynthesis pathway in M. cordata

    To date, nearly 300 secondary metabolites, including 204 isoquinoline alkaloids have been identified from M. cordata using untargeted LC-MS metabolomics technology[10]. This breakthrough surpasses the limitations of traditional methods for isolating and identifying secondary metabolites in plants, guiding the targeted analysis of alkaloid metabolism and metabolic profiling in M. cordata. Using untargeted LC-MS metabolomics technology, nearly 2,000 characteristic ions were discovered in M. cordata. Through stable isotope 13C6-labeled tyrosine tracing experiments, 179 13C6-labeled compounds were identified[1]. A database search for the non-labeled counterparts of these 13C6-labeled compounds quickly identified 40 alkaloids and four non-alkaloids, providing evidence for determining the biosynthetic pathways of sanguinarine and chelerythrine in M. cordata.

    Targeted analysis of the metabolic accumulation patterns of intermediates in the biosynthesis of sanguinarine and chelerythrine in different developmental stages and organs of M. cordata, combined with transcriptomics, proteomics, and metabolomics analysis revealed the biosynthetic tissues and gene expression patterns of alkaloid biosynthesis at different growth stages. This study elucidated the biosynthetic pathways of sanguinarine and chelerythrine and discovered the pattern of synthesis by 'root-pod compartmentalized synthesis', where precursor compounds like protopine are primarily synthesized in the roots and then transported to the pods for the synthesis of sanguinarine[1,32]. Laser microdissection with fluorescence detection was used to separate different tissue cells in the roots of M. cordata. Combined with LC-MS targeted analysis of trace alkaloids in each tissue, this approach accurately identified the storage cells of the alkaloids, clarifying the 'synthesis-storage-transport-resynthesis' biosynthetic mechanism of sanguinarine, chelerythrine, and their precursors[33] (Fig. 5).

    Figure 5.  Isotope tracing of the biosynthetic pathways of sanguinarine and chelerythrine in Macleaya.
    DownLoad: Full-Size Img PowerPoint

    Integrated analysis of genomics, transcriptomics, metabolomics, and proteomics in M. cordata to elucidate the mechanisms of sanguinarine storage, synthesis, and transport

    In 2013, Zeng completed an integration of transcriptomic, proteomic, and metabolomic data to elucidate the biosynthesis of alkaloids in M. cordata and M. macrocarpa[32]. This study investigated the potential mechanisms of alkaloid biosynthesis in Macleaya species by analyzing transcriptomic, proteomic, and metabolomic data from 10 different samples collected at various times, tissues, and organs. The assembled and clustered transcriptomic data yielded 69,367 unigenes for M. cordata and 78,255 unigenes for M. macrocarpa. Through a multi-level comparative analysis of key gene expressions controlling enzymes in the alkaloid metabolic pathway, the research identified homologous genes for all functional genes in the sanguinarine biosynthesis pathway. This annotation provided foundational data for cloning functional genes in the sanguinarine pathway of M. cordata.

    In 2017, researchers first mapped the complete genome of M. cordata, making it the first Papaveraceae plant to have its whole genome sequenced[1]. The genomic results indicated that the genome size of M. cordata is 540.5 Mb with a heterozygosity rate of 0.92%, predicting 22,328 protein-coding genes, of which 43.5% are transposable elements. Additionally, 1,355 non-coding RNA (ncRNA) genes were identified in the M. cordata genome, including 216 rRNA, 815 tRNA, 75 miRNA, and 249 snRNA genes. Comparative genomics revealed a significant expansion of the flavoprotein oxidase gene family closely associated with sanguinarine synthesis, providing crucial insights into the evolutionary origin of the sanguinarine biosynthetic pathway in Macleaya. Through co-expression analysis of genes and metabolites, researchers successfully identified 14 genes, including flavoprotein oxidases, methyltransferases, and cytochrome P450 enzymes, involved in the biosynthesis of sanguinarine.

    Metabolic engineering for the biosynthesis of sanguinarine

    Recent advancements in genetic engineering have led to a series of modifications on the berberine bridge enzyme (McBBE), a rate-limiting enzyme in the biosynthesis of sanguinarine in M. cordata. These modifications included codon optimization and the design of N-terminal truncated mutants to enhance expression efficiency in heterologous hosts. By employing CRISPR-Cas9 gene editing technology, these optimized genes were successfully integrated into the genome of Saccharomyces cerevisiae. This integration resulted in a significant increase in the production of the key precursor, chelerythrine, achieving a yield 58 times higher than the original level[34]. This accomplishment not only underscores the tremendous potential of genetic engineering in enhancing the synthesis of secondary metabolites but also provides a crucial foundation for subsequent industrial production. Furthermore, the research team developed innovative methods for producing sanguinarine through a 'plant-microbe' co-fermentation system. This system involved the co-cultivation of engineered yeast strains with the non-medicinal parts of M. cordata — specifically, the leaves — in a specially designed co-fermentation reactor[35]. This novel approach effectively converted precursor substances from the leaves into sanguinarine, maximizing the utilization of the non-medicinal parts of M. cordata and reducing production costs. This co-fermentation system not only offers an efficient and sustainable new pathway for the production of valuable bioactive compounds like sanguinarine but also exemplifies the integration of plant biology and microbial biotechnology.

    In 2022, significant progress was made by Jiachang Lian's team, who successfully achieved the de novo biosynthesis of sanguinarine, reaching a yield of 16.5 mg/L[36]. After comprehensive metabolic engineering modifications, the current best-engineered yeast strain achieved a production titer of 448.64 mg/L for sanguinarine[37]. This achievement highlights the immense potential of modern biotechnology in promoting the effective utilization and industrial production of components from traditional medicinal plants. By leveraging advanced genetic engineering techniques, researchers have been able to enhance the efficiency of secondary metabolite production, opening up new possibilities for the pharmaceutical and biotechnology industries.

    The innovative approaches employed in this research, such as codon optimization, N-terminal truncation, and the use of CRISPR-Cas9 for gene editing, represent significant advancements in the field of synthetic biology. These methods not only improve the expression efficiency of key enzymes but also pave the way for the scalable production of complex bioactive compounds. The successful integration of plant and microbial systems in a co-fermentation setup demonstrates a promising strategy for sustainable and cost-effective production processes. This research not only advances our understanding of biosynthetic pathways but also sets the stage for future developments in the industrial application of traditional medicinal plant components

    Breeding research on M. cordata

    Molecular breeding of M. cordata

    In the fields of plant science and biotechnology, artificial genetic transformation technology has become a key tool for molecular breeding. In 2016, a genetic transformation system for Macleaya cordata based on Agrobacterium tumefaciens was successfully established[38]. Utilizing this system, key genes involved in sanguinarine biosynthesis, such as berberine bridge enzyme MCBBE[39] and MCP6H[40], have been overexpressed, demonstrating the significant potential of genetic engineering in enhancing the production of plant secondary metabolites. Additionally, a hairy root culture system for M. cordata and M. microcarpa mediated by A. rhizogenes has also been successfully developed[41,42]. Recently, a CRISPR/Cas9 gene editing system for M. cordata has been established. By re-editing the sanguinarine biosynthesis pathway, researchers have achieved a significant increase in sanguinarine content in transgenic materials[43]. These advancements highlight the potential of molecular breeding techniques to enhance the yield of valuable secondary metabolites in M. cordata, providing a foundation for future research and industrial applications.

    Study on the domestication and DUS testing guidelines of M. cordata

    Previously, wild M. cordata capsules were the primary source of raw materials for M. cordata-related products. However, the popularity of these products has led to a significant decline in wild resources year by year. In response, domestic research teams have developed a standardized cultivation technology system for M. cordata. This system encompasses various techniques, including seedling raising, field management, pest and disease control, harvesting, and primary processing, facilitating the shift from wild to cultivated varieties. Additionally, comprehensive research on the current state of resources and breeding has led to the establishment of 30 traits which form the M. cordata DUS testing guidelines. As a result of these efforts, the team has preliminarily identified a superior strain, 'Meibo 1', known for its high fruit yield and elevated haematoxylin content.

    The role of M. cordata in animal production and the mechanism and safety of sanguinarine as a feed antibiotic substitute

    Sanguinarine from M. cordata as a bioactive compound was initially used in Europe as feed additives to enhance flavor and stimulate appetite in food animals[44]. Studies have shown that M. cordata extracts are safe, with no adverse effects observed in target animals even at ten times the recommended clinical dose. Pharmacodynamic and clinical data indicate that long-term addition of M. cordata extracts at recommended doses has anti-inflammatory and growth-promoting effects, and total protopine alkaloids are effective in treating Escherichia coli-induced diarrhea in poultry.

    Research on the mechanism of antibiotic substitution revealed that M. cordata extract enhances intestinal health by increasing the abundance of lactic acid bacteria, which inhibit pathogenic microorganisms through competitive exclusion[2]. Sanguinarine inhibits the phosphorylation and ubiquitination of I-κB proteins, reducing the dissociation of p50 and p60, thereby inhibiting the activation of the NF-κB signaling pathway. This results in decreased expression of pro-inflammatory cytokines and reduced inflammation levels in animals[45]. Additionally, sanguinarine was found to enhance protein synthesis in animals by inhibiting tryptophan decarboxylase activity, thereby increasing amino acid utilization[46,47]. Based on the growth-promoting effects of M. cordata extract as an antibiotic substitute, Jianguo Zeng's team has developed a comprehensive feed technology focused on 'intestinal health, anti-inflammatory properties, and growth promotion'. This approach avoids the risk of antibiotic resistance associated with traditional growth-promoting antibiotics while still enhancing animal growth performance. This technology supports the development of antibiotic-free feed solutions and the use of non-antibiotic inputs in animal husbandry. Furthermore, chelerythrine in M. cordata, when used as an animal feed additive, interacts with phospholipids on bacterial membranes, increasing membrane fluidity and impairing respiration by disrupting proton motive force and generating reactive oxygen species, leading to reduced intracellular ATP levels. This dual action of downregulating the mobile colistin resistance gene mcr-1 and associated genes offers a new strategy to circumvent colistin resistance. These findings provide strong technical support for the development of antibiotic-free feeding practices and the creation of alternative growth-promoting solutions in animal production[48].

    M. cordata extract is the first traditional Chinese veterinary medicine product approved for feed use in China. It is widely used to improve animal production performance, enhance animal health, and replace growth-promoting antibiotics in feed. Weaning stress is a major factor causing diarrhea and growth inhibition in piglets. Adding M. cordata extract to their diet can improve small intestine morphology, enhance intestinal barrier function, and regulate intestinal microbiota homeostasis, thereby reducing diarrhea and improving growth performance[49−52]. During pregnancy, progressive oxidative stress and parturition stress can lead to metabolic disorders and increased inflammation in sows. Supplementing their diet with M. cordata extract can reduce inflammation, enhance antioxidant capacity, shorten farrowing duration, increase feed intake and milk production during lactation, and ultimately increase the weaning weight of piglets[53,54]. Environmental stress and pathogenic infections are significant threats to poultry intestinal health. Adding M. cordata extract to poultry feed can improve intestinal mucosal morphology, enhance intestinal barrier function, regulate microbial populations, and improve broiler growth performance[55−58]. High-fat and high-protein feed can cause intestinal damage in fish. Supplementing their diet with M. cordata extract can enhance intestinal antioxidant capacity, alleviate intestinal barrier damage, improve microbiota homeostasis, and thus increase survival and growth rates[59−61]. Ruminants have a unique rumen physiology where the microbiota plays a crucial role in nutrient digestion and metabolism. Studies have shown that adding M. cordata extract to dairy cow diets can regulate rumen microbial populations and reduce methane emissions, alleviate intestinal inflammation in weaned lambs[62], promote growth in meat sheep[63], increase milk yield in dairy goats, reduce somatic cell counts in milk, and improves milk quality[64].

    In addition to its applications in animal production, M. cordata extracts have been developed into various products due to their significant insecticidal and antibacterial properties. In 2021, they were registered as a new botanical pesticide in China and the United States for controlling greenhouse plant diseases such as powdery mildew and leaf spot disease. In the bioenergy sector, the combination of M. cordata extracts with trace elements cobalt and nickel can effectively accelerate the fermentation process of agricultural waste, increasing biogas production. Furthermore, Macleaya alkaloids are used in toothpaste and mouthwash for their sustained antibacterial activity, which helps treat periodontal disease and prevent bad breath[65]. These findings highlight the diverse applications and benefits of M. cordata in improving animal health and productivity, controlling plant diseases, and enhancing bioenergy production (Fig. 6).

    Figure 6.  This illustration showcases the versatile applications of alkaloids derived from M. cordata. The molecular structures of key alkaloids—chelerythrine, sanguinarine, allocryptopine and protopine—are depicted in the center. These alkaloids are utilized in enhancing digestion and improving feed efficiency in ruminants, boosting immunity and promoting growth in pigs, promoting health and growth in fish, improving health in poultry, serving as natural pesticides for crops, reducing methane emissions from ruminants to lower greenhouse gases, acting as antibacterial ingredients in toothpaste and mouthwash, and exhibiting potential anti-cancer activity in cancer treatment. The alkaloids from M. cordata demonstrate significant potential across various fields, from agriculture to medicine.
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    Future challenges and prospects

    M. cordata, a plant rich in bioactive compounds, holds vast potential for applications in medical and agricultural fields. However, future research faces multiple challenges and opportunities. Firstly, although substantial research has been conducted on the primary alkaloids in M. cordata, their regulatory mechanisms remain unclear. Future studies need to integrate multi-omics data and systems biology approaches to elucidate the molecular mechanisms regulating alkaloid biosynthesis in M. cordata, providing a theoretical foundation for precise metabolic pathway regulation.

    Secondly, the application of molecular breeding and metabolic engineering in M. cordata is still in its infancy. Effectively increasing the yield of specific bioactive compounds through genetic engineering, particularly achieving efficient biosynthesis and accumulation of key alkaloids like sanguinarine, will be a focus of future research. Despite the achievement of de novo synthesis of sanguinarine in yeast, the scalability of this production method remains challenging. It is necessary to assess the economic feasibility of these methods to ensure they can meet industrial demands without compromising quality or sustainability. Additionally, the long-term stability and consistency of genetically engineered strains and their products need to be ensured to avoid potential issues in production and application.

    Lastly, as the medicinal value of M. cordata becomes better understood, ensuring its sustainable use and the conservation of wild resources, while developing more high-value products, will be crucial for future development. Large-scale cultivation and utilization of M. cordata may pose potential environmental impacts, including changes in soil health, biodiversity, and local ecosystems, which are not sufficiently studied and require further investigation and evaluation.

    In summary, while the research and application prospects of M. cordata are promising, they also present a series of scientific and technical challenges. By fostering interdisciplinary collaboration and enhancing the integration of basic and applied research, these challenges can be overcome, enabling the efficient utilization and industrial development of M. cordata resources. Addressing the limitations in current research, particularly in ecological impact and production methods, will provide a more balanced perspective and guide future research toward sustainable and scalable solutions.

    Author contributions

    The authors confirm contribution to the paper as follows: study conception and design: Huang P, Zeng J; draft manuscript preparation: Huang P, Cheng P, Sun M, Liu X, Qing Z, Liu Y, Yang Z, Liu H, Li C, Zeng J. All the authors reviewed the results and approved the final version of the manuscript.

    Data availability

    Data sharing not applicable to this article as no datasets were generated or analyzed during the current study.

    Acknowledgments

    This work was supported by Hunan Provincial Natural Science Foundation of China (2023JJ40367 & 2023JJ30341).

  • The authors declare that they have no conflict of interest.

  • Supplemental Table S1 Statistics of various volatile substances in Chrysanthemum with different aroma types.
    Supplemental Table S2 Statistical table of sensory evaluation of chrysanthemum flavor.
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  • Cite this article

    Wang Z, Zhao X, Tang X, Yuan Y, Xiang M, et al. 2023. Analysis of fragrance compounds in flowers of Chrysanthemum genus. Ornamental Plant Research 3:12 doi: 10.48130/OPR-2023-0012
    Wang Z, Zhao X, Tang X, Yuan Y, Xiang M, et al. 2023. Analysis of fragrance compounds in flowers of Chrysanthemum genus. Ornamental Plant Research 3:12 doi: 10.48130/OPR-2023-0012
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Analysis of fragrance compounds in flowers of Chrysanthemum genus

  • 1.

    Beijing Key Laboratory of Development and Quality Control of Ornamental Crops, Department of Ornamental Horticulture, China Agricultural University, Beijing 100193, China

  • 2.

    Institute of Agri-food Processing and Nutrition (IAPN), Beijing Academy of Agriculture and Forestry Sciences, Beijing 100089, China

  • Received: 14 February 2023
  • Accepted: 19 April 2023
  • Published online: 27 June 2023
Ornamental Plant Research  3,  Article number: 12  (2023)  |  Cite this article

Abstract: Chrysanthemum is one of the four major cut flowers in the world, with high ornamental and economic value. Fragrance is an important ornamental character of chrysanthemum flowers, especially those consumed as tea and other foods, and the flower fragrance is the major determinant of the commercial value of chrysanthemum cultivars. Currently, however, the research on chrysanthemum flower fragrance is mainly focused on the composition and content of fragrant compounds, and a clear classification of fragrance types is lacking. Here, we divided chrysanthemum fragrance into six categories based on sensory evaluation and determined the identity and content of fragrant compounds of chrysanthemum accessions representative of each fragrance type by GC-MS. In addition, we analyzed the conserved aromatic substances responsible for the fruity fragrance type chrysanthemum with multi-functional development potential, providing a theoretical basis for creating new chrysanthemum germplasm with specific fragrance types. The results of this study can accelerate the breeding process of chrysanthemum accessions with new fragrance types.

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    Introduction

    • Chrysanthemum (Chrysanthemum × morifolium [Ramat.] Kitamura) is native to China and is cultivated for sale as fresh cut flowers, planting in ornamental gardens, landscaping, and medicinal use. Floral fragrance is an important trait which mediates the intraspecific and interspecific interactions of plants[1]. Floral volatiles can attract pollinators, which promotes sexual reproduction, as well as natural enemies of phytophagous insects, which prevents attack by insect pests[2]. In addition, volatile compounds protect plants from abiotic stresses, such as strong light, high temperature, and oxidative stress[3,4]. The importance of floral fragrance is receiving increased research attention.

      Floral fragrance is determined by the type and content of volatile organic compounds (VOCs)[5]. A variety of VOCs are synthesized in plants. Depending on their source, VOCs are classified into three categories: terpenoids, phenylpropanoids/benzenoids, and fatty acid derivatives[1].

      Terpenoids, which form the largest class of VOCs are composed of several isoprene (C5) structural units. Depending on the number of structural units, terpenoids are classified as monoterpene (C10), sesquiterpene (C15), and diterpene (C20) compounds[6]. For example, monoterpenoids are the main aromatic substances in rose (Rosa × hybrida) flowers[7] , while linalool and ionone are the main compounds in Osmanthus fragrans flowers[8].

      Phenylpropanoids/benzenoids for the second largest class of plant VOCs[9], however, the complete biosynthetic pathway of phenylpropanoid compounds remains unclear. According to current knowledge, the direct precursor of phenylpropanoid/benzenoid compounds is phenylalanine, which is synthesized mainly through the shikimate pathway[10]. The flower fragrance of Petunia (Petunia hybrida) is mainly attributable to phenylpropanoid/benzenoid compounds, among which benzaldehyde, phenylacetaldehyde and methyl benzoate are the most abundant[11].

      Fatty acid derivatives are the third group of plant volatile substances. Acetyl coenzyme A (acetyl CoA) is the precursor of fatty acid derivatives. Acetyl CoA enters the lipoxygenase (LOX) pathway, and produces volatile substances through a series of reactions. According to a recent study, (E) -2-hexenal is one of the main compounds responsible for the floral fragrance of carnation[12].

      Previous research on the floral fragrance of chrysanthemum has mainly focused on the identification of aromatic compounds. In chrysanthemum and its wild relatives, monoterpenoids and oxygenated monoterpenoids, including camphor, α-pinene, laurene, and eucalyptus alcohol, are the predominant volatile components[13]. Monoterpenoids and sesquiterpenoids, including hydrocarbons, esters, aldehydes, ketones, phenols, and organic acids, are the predominant compounds of chrysanthemum volatile oil[14]. Investigation of the relationship between the accumulation and release of terpenoids in 44 related species and cultivars of chrysanthemum revealed that the release of terpenoids is strongly correlated with their internal concentration, whereas the concentration of terpenoids is associated with the release of the compound and the size of the capitulum. Tubular florets have a greater impact on the release of volatile substances than ligulate florets. In addition, the involucre and receptacle serve as the main sites for the accumulation of terpenoids[15]. The volatiles of chrysanthemum cultivar 'Boju' are mainly eucalyptus alcohol, filifon, pyrethrone, and trans- and cis-pyrethroid acetates[16]. An aromatic wild species, Dendranthema indicum (Chrysanthemum indicum var. aromaticum) was introduced to breed aphid-resistant offspring through hybridization with Chrysanthemum nankingense. Nineteen compounds of aphid resistant lines were selected and cis-4-thujanol was confirmed to be an effective aphid repellent[17]. Thus, the composition and content of volatiles differ substantially among chrysanthemum species. Although the volatile substances of chrysanthemum have been researched, the classification of chrysanthemum fragrance has not yet been reported.

      As stated above, the aroma of flowers determines the commercial value of chrysanthemum cultivars, especially those used for tea and edible purposes. Because of long-term natural selection and evolution, the fragrance type of chrysanthemum is highly diverse. Nevertheless, previous research on chrysanthemum floral fragrance mainly focused on the determination of the volatile compounds and their contents, and research on the classification of chrysanthemum fragrance types is lacking. In this study, the aroma type of among a large sample of chrysanthemums was investigated using a sensory evaluation method, and volatile substances of representative chrysanthemums of each aroma type were analyzed by gas chromatography–mass spectrometry (GC–MS). Based on the aroma type, chrysanthemum accessions were classified into six categories, providing a theoretical basis for the accelerated breeding of new chrysanthemum germplasm with specific aroma types.

    Materials and methods

      Plant materials

    • Chrysanthemum materials used for fragrance classification were collected from major parks in Beijing (China) and the chrysanthemum resource garden at the Shangzhuang Experimental Station of the China Agricultural University, Beijing, China.

      Chrysanthemums used for GC-MS determination were Chrysanthemum × morifolium 'Qihuang', C. indicum L., C. × morifolium 'Bairuixiang', C. × morifolium 'Quehuan', C. × morifolium 'Xiaokuixiang', and C. × morifolium 'Sigong'.

      Artificial pollination

    • Rooted cuttings of 'Xiaokuixiang' were planted at the Shangzhuang Experimental Station (Beijing, China), and reproductive isolation was carried out. Artificial self-pollination was conducted at the onset of flowering. The seeds were collected when mature.

      Open hybridization with 'Xiaokuixiang' as the female parent

    • A chrysanthemum cultivar with the same flowering period as 'Xiaokuixiang' was planted on either side of the female parent ('Xiaokuixiang'). Sterilized tweezers were used to remove the stamens at the onset of flowering of 'Xiaokuixiang', and the upper portion of the corolla of the outer florets in the capitulum was removed to expose the pistils. The seeds were collected when mature.

      Sensory evaluation

    • The aroma type of chrysanthemum was determined by means of a questionnaire. The members of the research group randomly distributed questionnaires to recipients. The aroma types were determined after statistical analysis. On the basis of the questionnaire, 24 students and teachers who were familiar with chrysanthemums and had the ability to distinguish aroma types were invited as sensory evaluators to screen representative cultivars of each fragrance type.

      Solid phase microextraction

    • Flowering stems of chrysanthemum were cut with secateurs, immediately placed in a bucket containing clean water, and transported to the laboratory for sampling. The capitulum (0.2–1.0 g) of each chrysanthemum was placed in a sampling bottle, with three replicates per cultivar, and then 15 μL of the internal standard (43.25 ng/g ethyl decanoate) was added to each bottle.

      Solid phase extraction head comprised 50/30 μm divinylbenzene/carbon/polydimethyl siloxane. The sample was placed in a 15 ml glass bottle in a 45 °C water bath, the extraction head was inserted, and the headspace was extracted for 30 min. The extraction head was analyzed in the 250 °C injection port for 3 min.

      Gas chromatography–mass spectrometry

    • The GC-MS analysis was conducted using a GCMS-QP2010 mass spectrometer (Shimadzu, Kyoto, Japan). The chromatographic conditions were as follows: injection port temperature, 250 °C; injection mode, split flow; total flow rate, 27.4 mL/min; split ratio, 20; ion source temperature, 200 °C; and interface temperature, 250 °C.

      The total analysis time was 30 min. The initial temperature was 40 °C, held for 1 min, then increased to 280 °C at 10 °C/min, held for 5 min, and the solvent delay time was 2.5 min. Mass spectrum conditions were: detector, 1 kV; mass scanning range 30–500 m/z; and full scanning mode.

      Statistical analysis

    • All determinations were performed with three biological replicates. Microsoft Excel and Graphpad Prism 8 were used to process and analyze the data. The results are expressed as the mean ± standard deviation (SD). Statistical significance was assessed using one-way analysis of variance (p < 0.05).

    Results

      Sensory evaluation and analysis of chrysanthemum flavor aroma

    • To classify the fragrance types of chrysanthemums, we performed sensory evaluation of the aroma characteristics of 520 chrysanthemum accessions. The fragrance of chrysanthemums could be grouped into six types: chrysanthemum fragrance, artemisia, medicinal, sweet, perfume fragrance, and fruity (Fig. 1). Among these types, chrysanthemum fragrance accounted for 30% of the cultivars, artemisia for 27.5%, medicinal for 20.0%, sweet for 6.0%, perfume fragrance for 6.5%, fruity for 3.5%, and others for 6.5%.

      Figure 1. 

      Statistical distribution of fragrance types in chrysanthemum accessions.

      According to the sensory evaluation results, the chrysanthemum accessions with the highest score in each fragrance type was selected as the representative of that category. The results showed that 91.67% of the evaluators considered that 'Sigong' was the most typical chrysanthemum cultivar with chrysanthemum fragrance, 91.67% considered that wild chrysanthemum (Chrysanthemum indicum L.) was the most typical chrysanthemum with artemisia fragrance, 87.50% considered that 'Qihuang' was the most typical cultivar chrysanthemum with medicinal fragrance, 75.00% considered that 'Quehuan' was the most typical chrysanthemum cultivar with sweet fragrance, 79.17% considered that 'Bairuixiang' was the most typical chrysanthemum cultivar with perfume fragrance, and 83.33% considered 'Xiaokuixiang' was the most typical chrysanthemum cultivar with fruity fragrance (Table 1). Therefore, to further analyze the aroma components of chrysanthemums of different fragrance types, the identity components and contents of the volatile substances were determined by selecting 'Sigong', C. indicum, 'Qihuang', 'Quehuan', 'Bairuixiang', and 'Xiaokuixiang' as the representative accessions of the chrysanthemum fragrance, artemisia, medicinal, sweet, perfume fragrance, and fruity fragrance, respectively (Fig. 2).

      Table 1.  Statistics foruation of chrysanthemum fragrance.

      Chrysanthemum cultivarsChrysanthemum
      fragrance (%)      		Artemisa
      fragrance (%)      		Medicinal
      fragrance (%)      		Sweet
      fragrance (%)      		Perfume
      fragrance (%)      		Fruity
      fragrance (%)
      Sigong91.678.330000
      Chrysanthemum indicum8.3391.670000
      Qihuang012.5087.50000
      Quehuan16.670075.0008.33
      Bairuixiang00012.5079.178.33
      Xiaokuixiang00012.504.1783.33

      Figure 2. 

      Chrysanthemum materials used in the experiment. (a) Chrysanthemum indicum L.; (b) C. × morifolium 'Xiaokuixiang'; (c) C. × morifolium 'Quehuan'; (d) C. × morifolium 'Bairuixiang'; (e) C. × morifolium 'Qihuang'; (f) C. × morifolium 'Sigong'.

      Identity and content of VOCs in chrysanthemum accessions of different aroma types

    • To explore the biochemical basis of different chrysanthemum fragrance types, the identity and content of volatile substances of representative chrysanthemum accessions were determined by GC–MS. Terpenoids were predominant in C. indicum (artemisia fragrance) and fatty acid derivatives were the most in 'Xiaokuixiang' (fruity fragrance), and the number of phenylpropanoid/benzenoid compounds was low in accessions of all fragrance types (Supplemental Table S1). As shown in Fig. 3, accessions with chrysanthemum fragrance, artemisia, medicinal, sweet, and perfume fragrance were dominated by terpenoids, accounting for more than 50% of all VOCs, followed by fatty acid derivatives, however, no significant difference was observed in the types and proportions of terpenoids and fatty acid derivatives in the of 'Xiaokuixiang' (fruity fragrance).

      Figure 3. 

      Proportions of volatile organic compounds in chrysanthemum with different fragrance types.

      To compare the differences among chrysanthemum accessions of different aroma types, the VOCs of different fragrance types were analyzed quantitatively. As shown in Fig. 3, except for 'Xiaokuixiang', other representative chrysanthemum accessions showed the highest content of terpenoids. Fatty acid derivatives were the most volatile substances.

      In 'Sigong', terpenoids were the most abundant, followed by fatty acid derivatives, and lastly phenylpropanoids/benzenoids. Eucalyptol was the main terpenoid, (E)-2-hexenal was the main fatty acid derivative, and o-cymene was the main phenylpropanoid/benzenoid compound (Fig. 4a). The compounds with the highest contents in 'Sigong' were eucalyptol, 2-pinene-6-one, and α-pinene, with the contents of 2,158.89, 849.00 , and 743.28 ng/µL/g, respectively (Fig. 4a).

      Figure 4. 

      Analysis of main volatile substances in Chrysanthemum with different fragrance types. (a) Analysis of main volatile substances in 'Sigong' with chrysanthemum fragrance; (b) Analysis of main volatile substances in Chrysanthemum indicum with artemisia fragrance; (c) Analysis of main volatile substances in 'Qihuang' with medicinal fragrance; (d) Analysis of main volatile substances in 'Bairuixiang' with perfume fragrance; (e) Analysis of main volatile substances in 'Quehuan' with sweet fragrance; (f) Analysis of main volatile substances in 'Xiaokuixiang' with fruity fragrance. FW: fresh weight.

      In C. indicum (artemisia fragrance), terpenoids were the most abundant, followed by fatty acid derivatives and phenylpropanoid/benzenoid compounds (Fig. 4b). D-camphor, β-myrcene, and eucalyptol were the main terpenoids (595.18, 214.92, and 143.53 ng/µL/g, respectively), and o-cymene was the main phenylpropanoid/benzenoid (Fig. 4b).

      In 'Qihuang' (medicinal fragrance), the content of terpenoids was the highest, followed by fatty acid derivatives and phenylpropanoid/benzenoid compounds (Fig. 4c). Eucalyptol was the main terpenoid compound, and (E)-2-hexenal and o-cymene were the main fatty acid derivatives and phenylpropanoid/benzenoid compounds, respectively (Fig. 4c). Eucalyptol, β-phellandrene, and (1S)-(−)-β-pinene showed the highest concentrations in 'Qihuang' (430.24, 109.42, and 105.67 ng/µL/g, respectively) (Fig. 4c).

      In 'Bairuixiang' (perfume fragrance), the content of fatty acid derivatives was the highest, followed by terpenoids, and that of phenylpropanoid/benzenoid compounds was lowest (Fig. 4d). (E)-2-hexenal was the main component of fatty acid derivative, whereas ocimene, β-myrcene, and linalool were the main components among terpenoids (Fig. 4d). (E)-2-hexenal, ocimene and β-myrcene showed the high concentrations in 'Bairuixiang' (504.72, 136.79, and 133.58 ng/µL/g, respectively) (Fig. 4d).

      In 'Quehuan' (sweet fragrance), the content of terpenoids were the most abundant, followed by fatty acid derivatives and phenylpropanoid/benzenoid compounds (Fig. 4e). β-myrcene, α-thujene and umbellulonl were the main components among terpenoids, (E)-2-hexenal were the main fatty acid derivatives, and o-cymene was the main phenylpropanoid/benzenoid compounds (Fig. 4e). The compounds with the high contents were β-myrcene, o-cymene, and α-thujene (1,236.08，604.88 and 537.86 ng/µL/g, respectively) (Fig. 4e).

      In 'Xiaokuixiang' (fruity fragrance) fatty acid derivatives were the most abundant, followed by terpenoids (Fig. 4f). (E)-2-hexenal and methyl salicylate were the main fatty acid derivatives, and (E)-β-farnesene and (E)-β-ocimene were the main terpenoids (Fig. 4f). The compounds with the high contents in 'Xiaokuixiang' were (E)-2-hexenal, (E)-β-farnesene, and methyl salicylate (78.94, 49.94, and 26.88 ng/µL/g, respectively) (Fig. 4f).

      Volatile organic compounds specific to accessions of different fragrance types

    • The preceding analysis showed that (E)-2-hexenal was the main volatile substance associated with the chrysanthemum, medicinal, perfume, and fruity fragrance types, and that eucalyptol was the main volatile substance associated with chrysanthemum, artemisia, and medicinal fragrance types. 2-Pinene-6-one, α-pinene and sabenene were the main volatile substances peculiar to the fragrance of 'Sigong', bornyl acetate was the main volatile substance peculiar to the artemisia fragrance of C. indicum. (1S)-(−)-β-pinene and β-phellandrene were the main volatile substances peculiar to the medicinal fragrance of 'Qihuang', ocimene and linalool were the main volatile substances peculiar to the perfume fragrance of 'Bairuixiang', 3-thujene and umbellulon were the main volatile compounds unique to the sweet fragrance of 'Quehuan', and methyl salicylate, (E)-β-ocimene, and 1-octene were the main volatile compounds unique to the fruity fragrance of 'Xiaokuixiang' (Fig. 5).

      Figure 5. 

      Bubble chart of volatile organic compounds specific in different fragrance types of chrysanthemum accessions.

      Analysis of aroma compounds of 'Xiaokuixiang' at different development stages

    • As shown in Fig. 6a, 'Xiaokuixiang' flowers were collected at three stages: bud stage, early flower stage and full flower stage. The aroma substances released by flowers at these three stages were divided into four categories: terpenoids (47%), fatty acid derivatives (32%), phenylpropanoid/benzenoid compounds (5%) and others (16%) (Fig. 6b). Quantitative analysis of different volatile substances showed that the content compounds were (E)-β-farnesene, (E)-2-hexenal, methyl salicylate and hexanal were high (Fig. 6c).

      Figure 6. 

      Analysis of volatile substances in different stage of flower in 'Xiaokuixiang' . (a) Different stage of flower in 'Xiaokuixiang'; (b) Proportions of volatile organic compounds in three stages; (c) Analysis of main volatile substances in different stage of flower in 'Xiaokuixiang'.

      Analysis of fragrance types in 'Xiaokuixiang' offspring

    • To analyze the genetic heritability of fruity fragrance type, we obtained 248 self-pollinated progenies and 383 hybrid progenies from 'Xiaokuixiang' as the female parent. Then, we determined the volatile substances of eight fruit-scented progenies by GC-MS (Supplemental Table S2), and compared the results with the volatile substances identified in 'Xiaokuxiang' . Ten volatile compounds were identified in nine fruit-scented chrysanthemums (Fig. 7), namely (E)-β-farnesene, 1-octene, caryophyllene, α-bergamotene, 1-hexanol, butanoic acid 2-methyl ethyl ester, butanoic acid 2-methyl propyl ester, butanoic acid 3-methyl hexyl ester, hexanoic acid ethyl ester and hexanal (Fig. 8).

      Figure 7. 

      Analysis of conserved volatile compounds in 'Xiaokuixiang' and its offsprings. Different colors represent different accessions.

      Figure 8. 

      A model for the fragrance types of chrysanthemum and main volatile substances of fruity fragrance. There is the classification and representative chrysanthemum of every fragrance type on the left, main volatile substances of fruity fragrance are on the right.

    Discussion

    • Flower fragrance is an important trait of flowering plants. It not only attracts pollinators for sexual reproduction but also promotes the interaction between plants and the environment, thus protecting plants from attack by pathogens, parasites, and herbivores[18,19]. Chrysanthemum is an important commercial floriculture crop. After long-term interspecific hybridization and artificial selection, a variety of chrysanthemum types have been developed, which are enriched in secondary metabolites that affect the floral fragrance of chrysanthemum.

      Aroma, as a trait perceptible by humans is particularly suitable for determining the fragrance type of chrysanthemum accessions through sensory evaluation. At present, the sensory evaluation method is used more systematically for the perception of food flavors. Although the sensory evaluation procedure for ornamental plants is not perfect, we used a relatively simple and convenient sensory evaluation method, employing a questionnaire survey to directly evaluate the perception of chrysanthemum fragrance. Through sensory evaluation of the fragrance of a large collection of accessions, we classified the accessions into six fragrance types: chrysanthemum fragrance represented by 'Sigong', artemisia fragrance represented by wild chrysanthemum, medicinal fragrance represented by 'Qihuang', sweet fragrance represented by 'Quehuan', perfume fragrance represented by 'Bairuixiang', and fruity fragrance represented by 'Xiaokuixiang'. Ongoing research will help improve the sensory evaluation of the aroma of ornamental plants.

      Aroma is dependent on volatile substances perceived by olfactory organs[20]. Therefore, the fragrance of plants is determined by the type and content of volatile substances. Detection of volatile substances responsible for the floral fragrance of chrysanthemum by GC-MS indicated that the main volatile substances in most chrysanthemums accessions were terpenoids (Fig. 3). The finding that terpenoids are important components of floral fragrance in chrysanthemum is consistent with previous studies[15].

      Further analysis showed that eucalyptol, 2-pinene-6-one, and α-pinene were the main volatile substances responsible for the fragrance of 'Sigong' (Fig. 4a). D-camphor, myrcene, and eucalyptol for artemisia fragrance (Fig. 4b), eucalyptol, β-phellandrene and (1S)-(-)-β-pinene for the medicinal fragrance of 'Qihuang' (Fig. 4c) and β-myrcene, o-cymene, and α-thujene for the sweet fragrance of 'Quehuan' (Fig. 4e). Previous studies have reported that the main volatile compounds of German chamomile (Matricaria recutita) are sesquiterpenes and monoterpenes, including (−)-γ-elemene, β-elemene, piperone, o-cymene, 3-perylene, and γ-terpene. The main volatile compounds reported for Roman chamomile (Chamaemelum nobile) are esters, including 3-methyl-2-butenoic acid, 3-methyl-2-alkenyl ester, 3-methyl-2-enoic acid, 2-methyl butyl ester, and 3-methyl-2-butenoic acid allyl ester[21]. These results indicate that the differences in volatile substances also exist among the different species of chamomile. 'Xiaokuixiang' is a novel chrysanthemum cultivar with a unique fragrance (fruity type) developed in the laboratory, whereas 'Bairuixiang' with perfume fragrance is a hybrid offspring of 'Xiaokuixiang'. The main volatile substances of 'Bairuixiang' are D-camphor, ocimene, and β-myrcene (Fig. 4d), and those of 'Xiaokuixiang' are (E)-2-hexenal, (E)-β-farnesene, and methyl salicylate (Fig. 4f). Analysis of the components of the various fragrance types by GC-MS revealed that the identity and content of the main volatile substances differed considerably among chrysanthemum cultivars.

      However, the content of volatile substances alone cannot confirm the characteristic volatiles of each chrysanthemum accession. Given the diversity and complex composition of volatile substances, their absolute content is not the only standard to measure their contribution to fragrance, an additional important factor is the aroma threshold of volatile substances[22]. Aroma threshold is a quantitative expression of aroma[23]. At a certain concentration, the lower the aroma threshold, the stronger the aroma of the substance, and vice versa. Furthermore, the aroma threshold of a of volatile substance changes under different conditions and in different solvents Therefore, based on the quantitative data obtained for the volatile substances in the present study, we could only determine the chrysanthemum fragrance type through sensory evaluation, and the main volatile substances that contribute to each fragrance type. Determination of the characteristic aromatic substances responsible for each fragrance type requires further investigation. Overall, we divide chrysanthemum accessions into six categories based on the sensory evaluation of floral fragrance, and found a novel fragrance type (fruity) chrysanthemum. Furthermore, this work provides a theoretical basis for the accelerated breeding of new chrysanthemum germplasm with specific aroma types.

    Conclusions

    • Chrysanthemum is an important ornamental and horticultural crop. However, there is no clear classification of its fragrance types. The results of this study divided chrysanthemum fragrance into six categories by sensory evaluation. We determined the types and content of VOCs in each chrysanthemum accession representative of different fragrance types by GC-MS. Furthermore, through genetic analysis, we determined the heritable aromatic substances of fruity fragrance chrysanthemum. Our present findings systematically classified the fragrance types of chrysanthemums and improved classification of chrysanthemum aroma types, providing a theoretical basis for the accelerated breeding of new chrysanthemum germplasm with specific aroma types.

      Acknowledgments

      • This work was supported by National Natural Science Foundation (Grant no. 32002072).

      Conflict of interest

      • The authors declare that they have no conflict of interest.

      • # These authors contributed equally: Zhiling Wang, Xin Zhao

      Supplementary information
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      • Copyright: © 2023 by the author(s). Published by Maximum Academic Press, Fayetteville, GA. This article is an open access article distributed under Creative Commons Attribution License (CC BY 4.0), visit https://creativecommons.org/licenses/by/4.0/.
    Figure (8)  Table (1) References (23)
  • About this article
    Cite this article
    Wang Z, Zhao X, Tang X, Yuan Y, Xiang M, et al. 2023. Analysis of fragrance compounds in flowers of Chrysanthemum genus. Ornamental Plant Research 3:12 doi: 10.48130/OPR-2023-0012
    Wang Z, Zhao X, Tang X, Yuan Y, Xiang M, et al. 2023. Analysis of fragrance compounds in flowers of Chrysanthemum genus. Ornamental Plant Research 3:12 doi: 10.48130/OPR-2023-0012
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Catalog

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  • Introduction
  • Materials and methods

  • Plant materials

  • Artificial pollination

  • Open hybridization with 'Xiaokuixiang' as the female parent

  • Sensory evaluation

  • Solid phase microextraction

  • Gas chromatography–mass spectrometry

  • Statistical analysis

  • Results

  • Sensory evaluation and analysis of chrysanthemum flavor aroma

  • Identity and content of VOCs in chrysanthemum accessions of different aroma types

  • Volatile organic compounds specific to accessions of different fragrance types

  • Analysis of aroma compounds of 'Xiaokuixiang' at different development stages

  • Analysis of fragrance types in 'Xiaokuixiang' offspring

  • Discussion
  • Conclusions
  • Acknowledgments
  • Conflict of interest
  • Supplementary information
  • Rights and permissions
  • About this article

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