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Article

An Analysis of Volatile Compounds and Study of Release Regularity in the Flower of Amorphophallus titanum in Four Periods

by
Dongyan Liu
1,†,
Peng Zhang
2,†,
Donghuan Liu
1,
Yuan Feng
2,
Miao Chi
1,
Ziyu Guo
2,
Xi Wang
1,
Jian Zhong
2 and
Ming Sun
2,*
1
Beijing Botanical Garden, Beijing Floriculture Engineering Technology Research Centre, Beijing 100093, China
2
Beijing Key Laboratory of Ornamental Plants Germplasm Innovation and Molecular Breeding, National Engineering Research Center for Floriculture, Beijing Laboratory of Urban and Rural Ecological Environment, Key Laboratory of Genetics and Breeding in Forest Trees and Ornamental Plants of Ministry of Education, School of Landscape Architecture, Beijing Forestry University, Beijing 100083, China
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Horticulturae 2023, 9(4), 487; https://doi.org/10.3390/horticulturae9040487
Submission received: 13 March 2023 / Revised: 10 April 2023 / Accepted: 11 April 2023 / Published: 13 April 2023
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Abstract

:
Titan arum (Amorphophallus titanum) is a rare and endangered plant in the world. It has a huge flower and releases a repulsive odor like a corpse. On the evening of 23 July 2022 (Beijing time), a titan arum in the north garden of the China National Botanical Garden in Beijing bloomed. In order to determine the components and contents of volatile compounds released by the titan arum during its flowering, the dynamic headspace adsorption method was utilized to collect the odor of the titan arum flower on the evening of 23 July (S1), the morning of 24 July (S2), the afternoon of 24 July (S3) and the evening of 24 July (S4). The volatile compounds were analyzed by automatic thermal desorption–gas chromatography/mass spectrometry. Sixty-three volatile compounds were detected in the titan arum flower in four periods. The comparison of the total volatile compounds released in four periods was S2 > S3 > S1 > S4. The highest content of volatile compounds in the S1 period were sulfur compounds (dimethyl disulfide and dimethyl trisulfide), and the sulfur compounds were released in large amounts only in the S1 period. Dimethyl disulfide was the volatile substance with the highest content in the S1 period (20.00%). The total volatile compounds content of titan arum flower in the S2 period was the highest among the four periods. From the S2 period, the relative content of sulfur compounds decreased significantly until the S4 period. Compared with the S1 period, 1-butanol and butyl acrylate increased significantly and 1-butanol became the highest relative component of volatile compounds in the S2 period. After the S3 period, the total amount of volatile compounds began to decline and reached the lowest level in the S4 period. It is worth noting that the contents of two terpenes, α-pinene and γ-terpinene, rose from the S1 period until their height in the S3 period. From the S4 period, the contents of most volatile compounds decreased significantly. This study revealed the varieties and contents of volatile compounds in the titan arum flower at different flowering periods. The changing trend and physiological significance of dimethyl oligosulfide from the evening of flowering (S1) to the second day (S2–S4) were emphatically discussed, and this research also provides a reference for the study of the release of volatile compounds and the molecular biology of the flower fragrance of titan arum.

1. Introduction

The titan arum (Amorphophallus titanum), a member of the Araceae family, is native to the Indonesian island of Sumatra. The titan arum belongs to the perennial bulb plant, and it begins to bloom only when the bulb reaches a certain size and stores enough nutrients. The titan arum has a huge flower, which is the largest recorded unbranched inflorescence [1]. It also releases an unpleasant odor similar to a corpse. The titan arum is a rare and endangered plant in the world, and requires challenging circumstances to bloom. Therefore, it is recognized as one of the most peculiar greenhouse plants in the world.
Titan arum belongs to a ‘deceptive’ plant, especially its flower. The deep-purple spathe mimics rotten meat and the odor mimics a rotten corpse to attract insects for pollination [2,3,4]. During the peak flowering stage, the temperature of the titan arum spadix can even reach 36 °C. This temperature is similar to a freshly dead animal, to further attract insects. These processes need lots of energy and thus the flower-opening time of the titan arum generally does not exceed a long time [4].
Plant volatiles are composed of many low molecular weight volatile organic compounds (VOCs). Normally, petals are the main source of volatiles, and other tissues (such as stamens, pistils and sepals) can also release small amount of volatiles [5]. Most flowers’ volatile compounds contain terpenes, phenylpropanoids/benzene compounds and fatty acid derivatives. They also includes some compounds containing nitrogen or sulfur [6]. Flower volatiles can attract insects to pollinate, just like the titan arum flower. In addition, flower volatiles are also a defense strategy against insects or animals harmful to plants [7,8,9].
So far, there are only one hundred flowering records about the titan arum in the world. Due to the short and indefinite flowering time, it is difficult to research the volatile compounds of flowers and there are few research results about it. The third titan arum bloomed in the north garden of China National Botanical Garden on the evening of 23 July 2022. Therefore, we utilized the dynamic headspace adsorption method to collect the volatiles of titan arum in four periods (evening of 23 July, morning of 24 July, afternoon of 24 July and evening of 24 July) and utilized an automated thermal desorption–gas chromatography/mass spectrometry (ATD-GC/MS) technique to analyze the volatile compounds in these four periods. This study is of great significance to reveal the changes of titan arum volatile compounds in different periods, and it is helpful for later research on the rhythmic changes and molecular mechanisms of volatile compounds’ release from titan arum.

2. Materials and Methods

2.1. Plant Material

On the evening of 23 July 2022 (Beijing time), a titan arum bloomed in the north garden of the China National Botanical Garden (Beijing, China). The titan arum was planted in May 2019 and bloomed for the first time after three years of planting. The titan arum’s inflorescence was 187 cm, and the maximum diameter of the spathe was 110 cm. We took this opportunity to research the volatile compounds of the titan arum. We collected the volatile compounds in four stages, at 20:00 on 23 July (S1), 8:00 on 24 July (S2), 14:00 on 24 July (S3) and 20:00 on 24 July (S4). Figure 1 shows the state of the titan arum flower at different periods.

2.2. Experimental Method

2.2.1. Collection of Volatiles

A dynamic headspace adsorption method was adopted to collect the volatiles of the titan arum in four periods. Before collection, the adsorption tubes containing Tenax GR adsorbent (CAMSCO, Houston, TX, USA, shown in Figure 2b) were needed to remove impurities. Nitrogen was added into the adsorption tubes at a rate of 100 mL/min and 270 °C for purging and activation for 120 min. The atmosphere sampling instrument (QC-1S) was used for odor collection (Beijing Keanlaobao New Technology Co., Ltd., Beijing, China); the odor also needed to be filtered by the drying column filled with activated carbon before it could be absorbed into the adsorption tubes, and odorless teflon tubes were used for the connection between the adsorption tubes, drying column and atmosphere sampling instrument. After connecting the instruments, titan arum volatiles were collected by referring to the method of a previous study [10]. The top of the teflon tube was inserted between the spathe and the spadix, as shown in Figure 2a. After that, the atmosphere sampling instrument was turned on and the air was extracted at the speed of 1 L/min for 30 min to collect volatiles into the adsorption tubes. The volatiles were collected three times in each period, and the air was used as the control. After collecting the volatiles, both ends of the adsorption tubes were tightened and wrapped with tinfoil, and then they were stored at −20 °C for testing.

2.2.2. Volatile Compounds Analysis

Volatile compounds were analyzed by the ATD-GC/MS technique: the sample in the adsorption tubes was heated and analyzed in the automated thermal desorber (Turbo Matrix 650, Perkin Elmer, Waltham, MA, USA), and the volatile compounds were brought into the GC-MS (Clarus 600T, PerkinElmer, Waltham, MA, USA) through inert carrier gas to analysis and identify the compounds. The carrier gas of the automatic thermal desorber was nitrogen and the flow rate was 1.5 mL/min. The first-order thermal desorption temperature was 260 °C, and the analysis time was 10 min. The cold trap capture temperature was −25 °C. The second-order thermal desorption cold trap was rapidly heated to 300 °C (40 °C/s). The valve temperature was 230 °C, the inlet temperature was 250 °C, and the gas split was 4%. The carrier gas of the GC was helium, and the chromatographic column was a DB-5MS capillary column (30 m × 0.25 mm × 0.25 μm). The initial temperature was 40 °C for 2 min, which then rose to 180 °C at the rate of 6 °C/min, and finally rose to 270 °C at the rate of 15 °C/min for 3 min. The ionization mode of MS was EI, and the electron energy was 70 EV, the scanning range of mass to charge ratio was 30~500 m/Z, the ion source temperature was 220 °C, and interface temperature of GC/MS was 250 °C.

2.2.3. Qualitative and Quantitative Analysis of Volatiles

The volatiles were analyzed by Turbo Mass 5.4.2 GC/MS software, the retrieval database was the NIST08 standard spectrum library, the corresponding peak area of each volatile was used for volatile metabolomic analysis, and the relative percentage content of each volatile component in the total volatiles was calculated by the ionic flow peak area normalization method.

2.2.4. Analysis of Volatile Metabolome

The Venn diagram, PCA diagram and cluster heat map for the volatile compounds of the titan arum flower in four periods were completed using the Metware Cloud (https://cloud.metware.cn, accessed on 22 August 2022). K-means cluster analysis is a popular and simple clustering algorithms, still widely used [11]. In order to study the trend of the content change of metabolites in different groups, K-means clustering analysis can be used [12]. Therefore, this study used K-means clustering analysis to analyze the content change trend of titan arum flower volatiles in four periods.
GraphPad Prism 8 software was utilized to draw the fan chart and column charts, and SPSS 22 software was utilized for multiple comparisons of nine important volatile compounds contents in different periods.

3. Results

3.1. Analysis on the Composition and Content of Volatile Compounds of Titan Arum Flower Volatiles in Four Periods

A total of sixty-three volatile compounds were detected in the titan arum flower in four periods. The cluster heat map was drawn by using the peak area of sixty-three volatile compounds in four periods, and the relative percentage content of each volatile component at each period was calculated by using the ionic flow peak area normalization method (relative percentage contents were not compared over different periods); the results are shown in Figure 3 and Table 1, respectively. The cluster heat map showed that the results of three technical repeated experiments in each of the four periods can be better clustered together.
According to the results of the peak area of volatile compounds in four periods, we found that the most volatile compounds were released in the S2 period, followed by S3 and S1, and the least volatile compounds were released in the S4 period (Figure 4a).
According to the results of the relative percentage content of each volatile compound in different periods (Table 1), we found that sulfur compounds (dimethyl disulfide and dimethyl trisulfide) were the main volatile compounds in the S1 period (the evening of 23 July, the day when titan arum bloomed); in this period, the relative content of dimethyl disulfide was the highest and the contents of dimethyl disulfide and dimethyl trisulfide accounted for 20.00% and 8.38% of the total contents, respectively. It is worth noting that these two sulfur compounds were released in large quantities only in the S1 period; their contents were greatly reduced in the other periods (S2–S4), to the extent that they could not become the most important volatile compounds. In addition, some volatile compounds such as 2-ethylhexanol, nonanal and decanal had high contents in all periods (S1–S4). Compared with the S1 period, the relative contents of 1-butanol (32.33%), dibutyl ether (3.17%) and butyl acrylate (9.64%) increased greatly in the S2 period, and reached their highest in this period. Compared with two previous periods (S1 and S2), the relative contents of 1,4-pentadiene (3.21%), decanal (10.94%), benzothiazole (3.07%), heptamethylnonane (6.13%) and tetradecane (5.91%) reached the highest in S3 period (the relative content of decanal was highest in the S4 period). We also detected some terpenes in the flower of titan arum. Among them, α-pinene and γ-terpinene were the two most prominent in relative contents, and their relative content proportion increased with the opening degree of flowers and reached the maximum in the S4 period.
Sixty-three volatile compounds were classified into eleven categories, including acid, alcohol, aldehyde, aliphatic hydrocarbon, aromatic compound, ester, ether, ketone, other, sulfur compound and terpene. The number of volatile compounds contained in these eleven categories is shown in Table 1. The compounds with the highest content in the four periods were sulfur compound (S1), alcohol (S2), aldehyde (S3) and aldehyde (S4). Second were aldehyde (S1), aldehyde (S2), aliphatic hydrocarbon (S3) and terpene (S4). The fan chart of the content proportion of these eleven substances in different periods is shown in Figure 4b.
In addition, we drew a Venn diagram according to the number of volatile compounds in the titan arum flower at each period (Figure 5a).

3.2. PCA of Volatile Compounds of the Titan Arum Flower in Four Periods

We performed PCA on the determination results of volatile compounds of the titan arum flower in four periods, as shown in Figure 5b; two principal components were used to represent the volatile compounds, with cumulative variance levels of 66.69% for PC1 (45.12%) and PC2 (21.57%).

3.3. Screening and Analysis of Important Volatile Compounds in the Titan Arum Flower

In order to screen important volatile compounds for further analysis, we utilized K-means cluster analysis to determine the release trend of sixty-three volatile compounds in different periods. The results of the K-means cluster analysis are shown in Figure 6a; we can find that the content change trend of sixty-three volatile compounds in four periods were divided into eight modules (Sub Class). We selected nine compounds with relatively high contents from the volatile compounds in each period: α-pinene, 1-butanol, 2-ethylhexanol, γ-terpinene, butyl acrylate, decanal, dimethyl disulfide, dimethyl trisulfide and nonanal. The peak areas of nine volatile compounds in different periods are shown in Figure 6b. Combined with K-means clustering analysis results, we found that among these nine volatiles 2-ethylhexanol, decanal and nonanal were divided into Sub Class 2, α-pinene and γ-terpinene were divided into Sub Class 3, 1-butanol and butyl acrylate were divided into Sub Class 4, and dimethyl disulfide and dimethyl trisulfide were divided into Sub Class 7.
We compared the changing trend of the peak area in nine important compounds at each period and made multiple comparative analyses (Duncan method). The results are shown in Figure 6b. We can find that the peak areas of two sulfur compounds (dimethyl disulfide and dimethyl trisulfide) in the S1 period were both significantly higher than those in other periods (S2–S4 period, p value < 0.05); the content of 1-butanol and butyl acrylate in S2 period was significantly higher than that in other periods (p value < 0.05). Two monoterpene compounds (α-pinene and γ-terpinene) had the highest content in S3 and the lowest content in S1, and the content of 2-ethylhexanol and two aldehydes (nonanal and decanal) in the S1–S3 period was generally higher than those in the S4 period.

4. Discussion

Amorphophallus has a rich morphological diversity; almost every plant organ shows remarkable variation, and plant size is probably one of the most obvious variable characteristics [14]. The titan arum is one of the most iconic members of Amorphophallus, and some studies have shown that the main volatile compounds of the titan arum flower are dimethyl disulfide and dimethyl trisulfide, and the odor similar to rotting animals comes from dimethyl trisulfide [10,15]. In addition to dimethyl disulfide and dimethyl trisulfide, extremely small amount of dimethyl tetrasulfide can also be produced in some species of Amorphophallus (including A. titanum); these sulfur compounds are also referred to as dimethyl oligosulphides and often described as having the smell of urine and rotten meat and vegetables [1,2,16]. Plants can display their flowers to the outside world through visual (such as shape and color) and gustatory (smell) methods. For some insects, the olfactory display of flowers is more specific than the visual display, so volatile compounds play a very important role in plant–insect interactions [17,18,19,20]. These unpleasant odors in the titan arum can attract some insects and bats to achieve the purpose of reproduction of the plants [21,22,23,24,25,26,27,28], especially Diptera or Coleoptera [29,30]. We summarized seven research results on the composition and content of volatile compounds in the flowers of titan arum, and found that our conclusions were consistent with most of the literature (Table 2). The main component in the titan arum flower at the S1 period (the night of flowering) was sulfur compounds, and the relative content of dimethyl disulfide was higher than that of dimethyl trisulfide.
In addition, Amorphophallus plants can also be classified according to different odors. Amorphophallus includes about 230 species. The genus is divided into four subgenera, namely Afrophallus, Amorphophallus, Metandrium and Scutandrium [4,16,28]. Kite and Hetterscheid studied the flower volatiles of eighty kinds of Amorphophallus plants and showed that dimethyl oligosulphides are released in species across all four subgenera, and nearly half of Amorphophallus plants were rich in dimethyl oligosulfide [16]. The plant material in this study is titan arum (A. titanum), which belongs to the subgenus Amorphophallus. Most species in this subgenus contain rich dimethyl oligosulfide, and titan arum is no exception. However, not all the flowers of Amorphophallus have unacceptable odors. Some species are sweetly scented, and these species contain 1-phenylethanol derivatives or 2-phenylethanol derivatives (4-methoxyphenylethanol); the former generally exists in the subgenus Metandrium, and the latter only exists in the subgenus Scutandrium. The odor type of these substances is completely different from that of carrion and feces, but these substances are also strong attractants of various beetle groups [28,31,32,33]. In this study, we also detected some aromatic compounds, but the content of each compound in four periods was not high, generally less than 1%; the total content of aromatic compounds in each period can reach about 15%.
In this study, we found that the content of dimethyl disulfide in the titan arum flower is higher than that of dimethyl trisulfide in the evening of the flower blooming; during the process of collecting gas, we could also smell the special odors of sulfur compounds. The threshold for dimethyl disulfide is higher [34,35]. Dimethyl disulfide is important for titan arums; it is common in vegetables. For example, the main volatile compounds in shiitake mushrooms (Lentinus edodes) include dimethyl disulfide and dimethyl trisulfide [36]; dimethyl disulfide could be evolved from methanethiol [37,38], and dimethyl trisulfide was presented to have many precursors, such as S-methylcysteine sulfoxide [39], sulforaphane (4-methylsulfinylbutyl isothiocyanate) [40], 1,2-dihydroxy-5-(methylsulfinyl)pentan-3-one (DMTS-P1) [41,42] and so on. Like dimethyl disulfide, dimethyl trisulfide can also evolved from methanethiol and methanethiol comes from methionine [43,44]. Some studies also posited that dimethyl disulfide is a precursor of dimethyl trisulfide [45,46,47]. There is no relevant research on the biosynthesis mechanism of sulfur compounds in titan arum or Amorphophallus, which needs further exploration.
Table
Table 2. Information on volatile compounds in the flower of titan arum in other works in the literature.
Table 2. Information on volatile compounds in the flower of titan arum in other works in the literature.
Published YearAuthors and LiteratureOdor Collection MethodMain Conclusions
1997Kite and Hetterscheid [2]Traps packed with Tenax GRDimethyl disulfide (75%), dimethyl trisulfide (10%)
1998Kite et al. [1]Traps packed with Tenax TADimethyl disulfide (10–90%), dimethyl trisulfide (1–10%)
2010Shirasu et al. [10]Solid phase microextraction (SPME)Volatile compounds absorbed to SPME: most were dimethyl disulfide, dimethyl trisulfide and methyl thiolacetate, and the main odorant causing the smell during the flower-opening phase was identified as dimethyl trisulfide
2012Fujioka et al. [15]Collected odors into the sample bagsDimethyl trisulfide (DMTS) is the main odor component of the flower detected by the human nose
2017Raman et al. [20]Modified headspace–solid phase microextraction (HS-SPME)Compounds such as butyric acid, g-butyrolactone, isovaleric acid, phenol, and trimethyl pyrazine in the appendix part of the inflorescence could contribute to the carrion-like odor of the bloom, and some sweet-smelling compounds such as butyl acetate, 4-hydroxy-4-methyl-2-pentanone, 2-ethyl hexanol, linalool, benzylalcohol, 2-phenoxyethanol and methyl dihydrojasmonate could also be detected
2017Kite and Hetterscheid. [16]Traps packed with Tenax TADimethyl disulfide (70%), dimethyl trisulfide (25%), dimethyl tetrasulfide (1%) and dimethyl pentasulfide (<1%)
2023Kang et al. [48]Thermal desorption tubesDimethyl disulfide was present in the highest abundance during the female flowering phase, followed by dimethyl trisulfide, methyl thiolacetate, methanethiol and 3-methylbutanal
From the previous description, we know that the most volatile compounds released in the night of flowering were dimethyl disulfide and dimethyl trisulfide, which are the most important sulfur compounds in the floral odor of titan arum. However, the content of both compounds greatly decreased on the second day of the titan arum flower opening. This is due to the large amount of energy consumed by the titan arum flowering, which releases a large amount of heat through respiration. On the one hand, the temperature of the inflorescence on the night of flowering can reach above 36 °C [3,49,50]. On the other hand, a higher temperature is conducive to the emission of volatile compounds. Some studies believe that heat generation is an important component of ‘cheating’ insects, and plants that produce heat and odors at the same time are more likely to attract pollinators than plants that produce odors alone [51,52]. Barthlott carried out a thermodynamic investigation on titan arums and found that when the flowers bloomed, the smell of corpse rot radiated in a wavy manner, which was synchronized with the rhythm of heat generation [3]. When we measured the volatile compounds of the titan arum in the evening of flowering (S1 period), we found that the content of dimethyl oligosulphides in this period was the highest; this result is consistent with the above research. However, in our research, we did not consider the wavy emission characteristics of volatile compounds, which may be a new research direction, and this is conducive to better understanding the principle of volatile compounds released during the flowering process of the titan arum. Due to the huge amount of energy consumed during the flowering period, the flowering period of titan arums usually lasts less than two days. In addition, the leaves and inflorescences of titan arums appear alternately in time. Only one of the leaves and inflorescences grows on the ground every year. Generally, after several years of leaf growth when tubers have accumulated enough nutrients, the inflorescences will develop [50]. In fact, we found a very interesting phenomenon when sampling the volatile compounds in the flower of titan arum: after the flowering night, the next morning we found that the spathe of the titan arum had constricted inwards obviously; at the same time, according to the above mentioned phenomenon in the thermodynamic study of titan arum flowers, the inflorescence temperature would gradually decrease to the same as the surrounding environment after flowering (the next morning). We speculate that the titan arum has completed its “mission” at this time, and when we measured the volatile compounds of flowers in this period (S2) we found that the content of dimethyl oligosulfide was significantly reduced, and the change trend in volatile compounds also corresponded to the change of inflorescence temperature. In the subsequent S3 and S4 periods, the content of dimethyl oligosulfide became lower and lower (Figure 7).
In addition to sulfur compounds, we also found that in titan arum, some aldehydes (nonanal and decanal), aliphatic hydrocarbons, aromatic compounds and esters always had high contents. In terpenes, we found that the content of two monoterpenes in the flower of the titan arum was higher—α-pinene and γ-terpinene—and the contents of two monoterpenes in S3 and S4 were more than those in S1 and S2. These volatile compounds became the important part of the flower fragrance of the titan arum. In fact, whether for the titan arum or other plants of Amorphophallus, the volatile compounds of flowers are composed of sulfur compounds, benzenoids, aliphatic acids, alcohols, ketones, esters, nitrogenous compounds and terpenoids. However, among different species, the proportion of various volatile compounds is different [16,20].

5. Conclusions

In this study, we determined the types and contents of volatile compounds in four blooming periods (S1–S4) of the titan arum flowers, and focused on the changes of two kinds of dimethyl oligosulfide (dimethyl disulfide and dimethyl trisulfide) in four periods, because sulfur compounds have the highest content in the evening of flowering (S1) in titan arum flowers, and sulfur compounds are also very important for titan arums (or plants of Amorphophallus). We also discussed the changing trends of seven other important volatile compounds in four periods. This research provides a reference for the study of the release of volatile substances from the titan arum flower, and the molecular biology of flower fragrance.

Author Contributions

Methodology, D.L. (Dongyan Liu), P.Z. and M.S.; Project administration, D.L. (Dongyan Liu), D.L. (Donghuan Liu), M.C. and X.W.; Resources, D.L. (Dongyan Liu) and D.L. (Donghuan Liu); Supervision, M.S.; Validation, P.Z.; Visualization, P.Z.; Writing—original draft, P.Z., Y.F., Z.G. and J.Z.; Writing—review and editing, J.Z. and M.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

All the data relevant to this work are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. The opening process of the titan arum flower (scale bar, 10 cm). The flower in peak flowering stages (S1–S4) of the titan arum were used to collect and detect volatile compounds.
Figure 1. The opening process of the titan arum flower (scale bar, 10 cm). The flower in peak flowering stages (S1–S4) of the titan arum were used to collect and detect volatile compounds.
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Figure 2. The method for collecting volatile compounds (a) and adsorption tubes (b).
Figure 2. The method for collecting volatile compounds (a) and adsorption tubes (b).
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Figure 3. The cluster heat map of the volatile compounds of the titan arum flower in four periods. The “red” squares represent high content, “blue” squares represent low content, and “pale” squares represent medium content.
Figure 3. The cluster heat map of the volatile compounds of the titan arum flower in four periods. The “red” squares represent high content, “blue” squares represent low content, and “pale” squares represent medium content.
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Figure 4. Column chart of the total compounds peak area (a) and fan charts of the content proportion of eleven categories of volatile compounds (b) in four periods. The Duncan multiple comparisons method was used to identify significant differences of peak areas of total volatile compounds (a) in four periods (p < 0.05), the groups with the same letter representing insignificant differences between them, and groups without the same letter representing significant differences between them.
Figure 4. Column chart of the total compounds peak area (a) and fan charts of the content proportion of eleven categories of volatile compounds (b) in four periods. The Duncan multiple comparisons method was used to identify significant differences of peak areas of total volatile compounds (a) in four periods (p < 0.05), the groups with the same letter representing insignificant differences between them, and groups without the same letter representing significant differences between them.
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Figure 5. Intersection of volatile compounds in four periods and principal component analysis (PCA) of the titan arum flower. (a) Venn diagram; (b) PCA diagram.
Figure 5. Intersection of volatile compounds in four periods and principal component analysis (PCA) of the titan arum flower. (a) Venn diagram; (b) PCA diagram.
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Figure 6. The results of K-means cluster analysis in all volatile compounds (a) and column charts of nine important volatile compounds (b) in four periods. Duncan multiple comparisons method was used to identify significant differences in nine key volatile compounds (b) in four periods (p < 0.05), the groups with the same letter representing insignificant differences between them, and groups without the same letter representing significant differences between them.
Figure 6. The results of K-means cluster analysis in all volatile compounds (a) and column charts of nine important volatile compounds (b) in four periods. Duncan multiple comparisons method was used to identify significant differences in nine key volatile compounds (b) in four periods (p < 0.05), the groups with the same letter representing insignificant differences between them, and groups without the same letter representing significant differences between them.
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Figure 7. Schematic of the effect of volatile components and inflorescence temperature of titan arum on insect attraction. The S1 period represents the night when the titan arum blooms, and the S2 period represents the morning of the next day.
Figure 7. Schematic of the effect of volatile components and inflorescence temperature of titan arum on insect attraction. The S1 period represents the night when the titan arum blooms, and the S2 period represents the morning of the next day.
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Table
Table 1. The results of the relative percentage content of each volatile compound in four periods.
Table 1. The results of the relative percentage content of each volatile compound in four periods.
No.Mea/Lite RI 1Volatile ComponentCASS1S2S3S4D/R Odor Threshold (mg/m3) 2
Acid (2)
M008576/610acetic acid64-19-70.98 0.68 1.34 1.09 0.001–10/0.05–25
M0531272/1273nonanoic acid112-05-0---0.57 0.02–0.12/0.0016–0.0032
Alcohol (3)
M002463/427ethanol64-17-50.83 0.04 0.16 0.21 0.17–1350/8.7–9230
M009662/6591-butanol71-36-31.66 32.33 1.00 -0.01–162/0.35–285
M039995/10302-ethylhexanol104-76-78.72 6.83 8.60 7.35 0.4–0.8/0.74
Aldehyde (8)
M001408/404acetaldehyde75-07-00.34 0.46 0.70 0.88 0.0027–1/0.027–10
M011643/6523-methylbutanal590-86-30.62 0.33 0.49 0.74 0.00035–0.0016/-
M015806/800hexanal66-25-11.25 0.69 1.44 3.42 0.0011–0.33/0.02–0.16
M025905/901heptanal111-71-7---1.06 0.00085–0.26/0.009–0.15
M0361005/1003octanal124-13-01.91 0.66 1.38 1.05 0.000052–0.17/0.005–0.01
M0431104/1104nonanal124-19-610.99 5.58 7.86 8.13 0.002–0.23/0.0096–0.06
M0501204/1206decanal112-31-28.39 6.00 10.94 10.98 0.0026–0.063/0.03–0.094
M0571402/1409dodecanal112-54-9--0.70 -0.033/0.014–0.033
Aliphatic hydrocarbon (10)
M004498/4641,4-pentadiene591-93-50.93 -3.21 3.12 -/-
M016788/8212,4-dimethyl-heptane2213-23-20.28 ----/-
M024916/900nonane111-84-2--0.96 -12/108
M032981/9912,2,4,6,6-pentamethylheptane13475-82-61.00 ----/-
M0351015/1000decane124-18-50.08 0.08 0.16 -3.6–160/-
M0491214/1200dodecane112-40-30.76 0.69 0.75 0.63 0.77–50/-
M0551294/1322heptamethylnonane4390-04-95.11 3.07 6.13 5.53 -/-
M0561413/1400tetradecane629-59-42.72 2.13 5.91 4.98 5/-
M0611512/1500pentadecane629-62-91.40 1.16 2.22 2.04 -/-
M0621612/1600hexadecane544-76-30.92 0.82 1.68 1.84 0.5/-
Aromatic compound (13)
M013794/763toluene108-88-31.46 2.08 2.02 3.83 0.12–590/3.5–260
M017893/855ethylbenzene100-41-40.95 0.62 0.55 0.76 0.026–78.3/-
M018907/866m-xylene108-38-33.20 1.90 0.78 1.67 0.052–86/1.1–2.4
M021907/887o-xylene95-47-61.18 0.77 0.57 1.05 0.77–23.6/1–3.1
M029982/962benzaldehyde100-52-70.86 0.96 1.53 0.97 <0.01–3400/0.33–4.1
M0331020/9901,2,4-trimethylbenzene95-63-60.11 0.24 0.35 0.35 0.14–0.7/0.3–1.1
M0381042/1022o-cymene527-84-40.59 0.68 2.04 1.28 -/0.004–0.005
M0411029/1065acetophenone98-86-20.70 0.50 0.95 0.66 0.01–1.5/2.9
M0461231/1182naphthalene91-20-30.75 0.99 1.28 1.18 0.007–0.45/0.05–5.34
M0511212/12252-phenoxyethanol122-99-60.29 0.22 0.81 1.02 -/-
M0541345/13071-methylnaphthalene90-12-00.37 0.32 0.47 --/-
M0591458/14361,4-dimethylnaphthalene571-58-4-0.32 0.83 0.59 -/-
M0631711/16923,4-diethylbiphenyl61141-66-01.82 1.48 3.85 3.72 -/-
Ester (7)
M007586/612ethyl acetate141-78-6-0.22 0.17 -0.88–623/3.6–270
M014761/767diethyl carbonate105-58-80.78 --0.18 -/-
M023874/861butyl acrylate141-32-20.71 9.64 2.51 0.80 0.0015–0.01/0.014
M027884/908butyl propionate590-01-20.13 0.78 0.40 0.19 0.19/-
M034984/995butyl butanoate109-21-70.11 0.20 0.18 0.15 0.028/-
M0441088/1059dimethyl 2-methylbutanedioate1604-11-1--1.14 0.23 -/-
M0471281/1192methyl salicylate119-36-80.27 0.25 0.42 0.50 0.002–119/0.0035–22.3
Ether (3)
M010657/6611-methoxy-2-propanol107-98-20.43 ---30.908–121/-
M019892/858dibutyl ether142-96-10.46 3.17 0.76 0.07 0.4–8/1.3
M026936/9062-butoxyethanol111-76-20.54 ---0.21–1.9/1.7
Ketone (6)
M003455/486acetone67-64-1-0.90 --1–27,900/4.1–1900
M005545/576methyl vinyl ketone78-94-40.58 0.68 0.89 -(0.5) 3
M006555/5982-butanone78-93-3--0.41 1.27 0.21–250/16–163
M020853/8873-heptanone106-35-40.43 ----/-
M022891/894cyclohexanone108-94-10.36 0.39 0.45 0.46 0.48–880/0.48
M0601420/1453geranyl acetone3796-70-1-0.44 1.25 1.12 -/-
Other (1)
M0521208/1229benzothiazole95-16-9-1.02 3.07 2.46 -/-
Sulfur compound (2)
M012722/746dimethyl disulfide624-92-020.00 0.94 0.34 0.63 0.0011–0.078/0.011–0.029
M030972/970dimethyl trisulfide3658-80-88.38 0.38 0.16 0.04 -/0.0073
Terpene (8)
M028948/937α-pinene80-56-81.44 3.36 5.55 9.06 0.1–105/25–29
M031993/1028p-mentha-1(7),3-diene99-84-30.23 0.69 0.96 1.79 -/-
M0371031/1060γ-terpinene99-85-40.91 1.83 4.73 6.69 2.5–55/1.4–1.6
M0401059/1032eucalyptol470-82-60.66 0.80 1.01 0.53 0.003–2/0.00062–0.05
M0421064/1088terpinolene586-62-90.46 -0.35 --/-
M0451164/1169menthol1490-04-61.47 0.93 1.84 1.68 -/-
M0481143/1189α-terpineol98-55-5-0.30 0.79 0.72 0.01–0.86/0.0125–110
M0581398/1405longifolene475-20-70.46 0.44 0.92 0.76 -/-
1 Kovats Retention Index (RI) could divided into Measured RI (Mea RI) and Literature RI (Lite RI); the Lite RI was obtained from the software NIST MS Search 2.3. 2 Odor threshold could be divided into detection odor threshold (D odor threshold) and recognition odor threshold (R odor threshold); data from the book Compilations of Odor Threshold Values in Air, Water and Other Media [13]. 3 Neither the detection nor recognition odor thresholds can be found, the value shown here is an unspecified type.
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Liu, D.; Zhang, P.; Liu, D.; Feng, Y.; Chi, M.; Guo, Z.; Wang, X.; Zhong, J.; Sun, M. An Analysis of Volatile Compounds and Study of Release Regularity in the Flower of Amorphophallus titanum in Four Periods. Horticulturae 2023, 9, 487. https://doi.org/10.3390/horticulturae9040487

AMA Style

Liu D, Zhang P, Liu D, Feng Y, Chi M, Guo Z, Wang X, Zhong J, Sun M. An Analysis of Volatile Compounds and Study of Release Regularity in the Flower of Amorphophallus titanum in Four Periods. Horticulturae. 2023; 9(4):487. https://doi.org/10.3390/horticulturae9040487

Chicago/Turabian Style

Liu, Dongyan, Peng Zhang, Donghuan Liu, Yuan Feng, Miao Chi, Ziyu Guo, Xi Wang, Jian Zhong, and Ming Sun. 2023. "An Analysis of Volatile Compounds and Study of Release Regularity in the Flower of Amorphophallus titanum in Four Periods" Horticulturae 9, no. 4: 487. https://doi.org/10.3390/horticulturae9040487

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