Comparative analysis of floral scent profiles between two Chimonanthus praecox plants under different rhythms and blooming stages
Introduction
Floral fragrances act to repel herbivores (Pichersky and Gershenzon, 2002; Unsicker et al., 2009), defend against pathogens (Arimura et al., 2004), protect flowers from harmful insects (Li et al., 2017, Li et al., 2016b), attract pollinators (Dudareva et al., 2004), communicate with other plants (Schiestl, 2010; Raguso, 2008), medical treatment of illnesses (Zhao et al., 2012), increase aesthetic value, and attract visitors (Clara de et al., 2014). Floral fragrances comprise low-molecular-weight volatile organic compounds (VOCs), which can be divided into four classes: terpenoids, phenylpropanoids/benzenoids, fatty acid derivatives, and compounds containing nitrogen/sulfur (Muhlemann et al., 2014). Terpenoids, phenylpropanoids/benzenoids, and fatty acid derivatives are the main floral scent compounds in ornamental plants, and the flowers of various ornamental plants contain different amounts of these three types of compounds. Some studies have shown that ornamental plants such as Bearded Irises (Yuan et al., 2019), Asarum yaeyamense (Azuma et al., 2010), Lilium brownii (Kong, 2012), Paeonia suffruticosa (Li et al., 2012), Dendranthema morifolium (Sun et al., 2015), and Luculia pinceana (Li et al., 2016) are rich in terpenoids, such as linalool, β-linalool, α-pinene, β-ocimene, α-selinene, β-selinene, and myrcene. Meanwhile, high phenylpropanoid/benzenoid contents (e.g., phenylethyl alcohol, phenethyl benzoate, benzyl benzoate, and butyl ethyl acetate) have also been found in ornamental plants such as Rosa damascena (Feng et al., 2010; Akbar et al., 2013), Nymphaea hybrida (Xu et al., 2011; Zhou et al., 2019), and Petunia hybrida (Negre et al., 2003; Haring et al., 2005). Typically, fatty acid derivatives, such as anisic aldehyde, (2E)-hexenal, 4-hexenyl acetate, and γ-decalactone, are the main floral volatiles in Prunus mume (Zhang et al., 2019), Eriobotrya japonica (Huang et al., 2019), Dianthus caryophyllus (Schade et al., 2001), and Osmanthus fragrans (Cao et al., 2009).
Floral scent profiles of Chimonanthus plants vary the most among species and geographical locations. Their profiles can also be influenced by developmental stages, the types of tissues that were sampled, and the season in which they were collected. Their scent compounds were mainly terpenes, benzene derivatives, alkanes, esters, acids, and other types of substances (Lin, 2019). The major scent compounds of C. praecox from Zhejiang province (Xu et al., 2016) are hedycaryol and α-myrcene, whereas those of C. praecox from Jiangxi province are dehydroaromadendrene and (−)-spathulenol (Xu et al., 2006). z-Muurolene and elemol are the main scent compounds of var. conclor from Sichuan province (Li et al., 2008), whereas alloocimene dominates in Hubei province (Zhou and Ni, 2010). Additionally, Pan (2017) reported differences in the floral scent compounds of var. conclor, var. intermedius, and the var. grandiflorus flowers from Jinhong and Nanjing and the main floral scent compounds are ocimene, ocimene isomer mixture, ocimene, and linalool, respectively. Linalool, benzyl acetate, methyl salicylate, and β-ocimene are the predominant scent compounds of C. praecox with the H29, H64, H36, and SW001, respectively (Feng, 2017; Xiong et al., 2012; Zhou et al., 2007; Li, 2015; Yu, 2013). As mentioned above, the composition and amount released of a floral scent are closely related to the geographical area and species. However, comparative analyses of floral scent compounds of C. praecox in Kunming, Yunnan province have been limited.
Earlier studies have reported changes in the composition, the amount released, and the emission rates of scents for C. praecox in various blooming stages. Numerous volatile compounds have been observed for C. praecox during five flowering periods (Li et al., 2009). Results have suggested that benzyl acetate is a major volatile compound during flower senescence, while β-linalool is the most abundant in flower buds and earlier flowering stages. Except in the flower bud stage, 4-trimethyl-3-(1-methylvinyl)-cyclohexane methanol is the major volatile compound during flowering period (Xie et al., 2008). In addition, the composition and amount released floral scents vary with circadian rhythm (Kolosova et al., 2001). Plants undergo changes to their floral aroma substances depending on circadian rhythm, including Houttuynia cordata (Chen et al., 2008), Chorizanthe breweri (Kolosova et al., 2001), Dendranthema morifolium (Sun et al., 2008), Lilium brownii (Zhang et al., 2013), and Osmanthus fragrans (Shi et al., 2018). For example, unlike snapdragons (Dudareva et al., 2003), petunias corollas release more methyl benzoate at night than during the daytime (Underwood et al., 2005). However, very little is known about the diversity of the floral scent compounds in C. praecox with different circadian rhythms. Studies fetching deeper insight into the changes in the composition and diversity of floral scent compounds in C. praecox from Yunnan would greatly assist the development of new fragrant cultivars and research on biosynthesis pathways in the future.
Therefore, the objective of this study is aimed at probing the amounts and diversity of floral scent compounds in two varieties of C. praecox during bud and fully-open flower stages and to explore diurnal change in their floral scent composition in the morning (7 a.m.), mid-day (1 p.m.), and evening (7 p.m.). In this study, we analyzed the floral scent compounds in C. praecox using headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography–mass spectrometry (GC-MS). To the best of our knowledge, this is the first report on the floral scent compounds of fresh C. praecox flowers from Yunnan under different circadian rhythms.
Section snippets
Plant material
C. praecox with different flower colors were selected in our study. var. grandiflorus from the Southwest Forestry University Campus and var. intermedius from Heilongtan Botanical Garden were used as the experimental material (Fig. 1). The morphological characteristics of var. grandiflorus included round dark-yellow petals, a purple flower center, ovoid leaves, and cylindrical gray-brown branches; var. intermedius had thin and pointed yellowish brown petals, a purple flower center, oval-ovate
Identification of floral scent compounds in C. praecox (var. grandiflorus and var. intermedius)
The floral scent compounds emitted by the flowers of the two varieties of C. praecox plants are shown in Table 1. A total of 69 floral scent compounds that can be divided into eight categories were identified. Ingredients such as 18 acids, 16 alcohols, 10 esters, 9 aromatic compounds, 5 terpenes, 4 aldehydes, 4 ketones, and 3 other substances could be detected. Chimonanthus praecox var. grandiflorus and var. intermedius flowers had similar amounts of floral scent compounds (53 and 52), but the
Discussion
The floral scents of C. praecox are correlated with the species and geographical area. In our study, a total of 69 floral scent compounds that could be divided into eight categories were identified in C. praecox. The numbers of floral scent compounds in var. grandiflorus (53) and var. intermedius (52) flowers were very similar, but the compositions varied greatly. The C. praecox flowers in this study emitted fewer floral scent compounds than do other species or cultivars, such as var.
Conclusions
The floral scent compounds in var. grandiflorus and var. intermedius with different circadian rhythms and at two blooming stages are found to be significantly different. A total of 69 floral scent compounds that could be divided into eight categories were identified in C. praecox. Though the numbers of floral scent compounds in var. grandiflorus (53) and var. intermedius (52) flowers were similar, and comparable the compositions varied greatly. M-xylene, p-xylene, 2-norbornanemethanol,
CRediT authorship contribution statement
Yue Li: Methodology, Formal analysis, Investigation, Data curation, Writing – original draft, Writing – review & editing, Visualization. Weijia Jia: Methodology, Investigation, Data curation, Writing – original draft. Qiong Wang: Investigation, Data curation, Writing – review & editing. Biao Wang: Conceptualization, Methodology, Writing – review & editing. Shu Wang: Conceptualization, Methodology, Formal analysis, Resources, Writing – original draft, Writing – review & editing, Supervision,
Declaration of Competing Interest
The authors declare no conflict of Interest.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (31860229) and Yunnan Ten Thousand People Plan (Youth Top Talent Project: YNWR-QNBJ-2019–028).
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These authors contributed equally to this work.