Chemical Composition of Floral Scents from Three Plumeria Rubra L
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Biochemical Systematics and Ecology 85 (2019) 54–59 Contents lists available at ScienceDirect Biochemical Systematics and Ecology journal homepage: www.elsevier.com/locate/biochemsyseco Chemical composition of floral scents from three Plumeria rubra L. T (Apocynaceae) forms linked to petal color proprieties Wei-Chang Gonga,1, Shi-Juan Xua,1, Yan-Hong Liua, Chuan-Ming Wanga, Konrad Martinc, ∗ Ling-Zeng Menga,b,c, a Xuefu Rd, College of Life Science and Technology, Honghe University, Mengzi, Yunnan, 661199, China b Xishuangbanna Tropical Botanical Garden, The Chinese Academy of Sciences, Mengla, Yunnan, 666303, China c University of Hohenheim, Institute of Agricultural Sciences in the Tropics (Hans-Ruthenberg-Institute) (490f), 70593, Stuttgart, Germany ARTICLE INFO ABSTRACT Keywords: The floral scents of three forms of cultivated Plumeria rubra L. were evaluated through mass flowering phenology Plumeria rubra using the dynamic headspace adsorption method and were identified with coupled gas chromatography and Floral scent mass spectrometry. The forms P. rubra f. acutifolia and P. rubra f. lutea had white and yellow flower petals, Flower color variation respectively, and the flower petals of P. rubra f. rubra were red. Although 68 components of the flower scents of Color-scent associations the three forms were recorded in different proportions, only 14 chemical compounds were identified withsta- Chemical composition tistically significance. The main volatile compounds in the red formof P. rubra L. were fatty acid derivatives Species specific (56.75%). The main compounds in the white and yellow forms of P. rubra L. were benzenoid and terpene, with proportions of 48.38% and 33.33% in P. rubra f. acutifolia and proportions of 42.30% and 47.43% in P. rubra f. lutea, respectively. These differences in the flower scents might be one result of the minor genetic differences between these forms, similar to the role of genetic differences in the flower color combinations of the three forms. We conclude that petal color traits can, to some extent, reflect differences in floral scent compositions and that minor genetic differences of different plant forms exert impacts not only on flower color butalsoonthe phytochemistry of floral scents. 1. Introduction volatile components of floral scents were believed to be the major vectors to deceptively attract pollination agents. Plumeria rubra L. is a typical tropical plant species that is originally Undoubtedly, floral color and scent are the most important attrac- native to Central and South America, including Mexico, Colombia and tants for pollinators (Chen et al., 2012; Knudsen and Tollsten, 1993; Venezuela. P. rubra L. has been widely cultivated in subtropical and Veiga et al., 2015). Such combinations have been documented among tropical climates worldwide and is a popular garden and park plant individuals of the same or different deceptive plant species (Dafni, because of its graceful morphology and refreshing aromatics. P. rubra L. 1984; Salzmann and Schiestl, 2007; Tollsten and Bergström, 1993). A has many different color morphs with mass-flowering phenology andis meta-analysis showed that the flower scent components and color dis- composed of fragrant flowers of shades of pink, white and yellow play specificity of deceptive-pollinated species are more variable than throughout the summer and autumn (Stephen, 2008). Moreover, P. in species offering a reward to pollinators (Ackerman et al., 2011). The rubra L. has been defined as a deceptive pollination species that does variation of the combination between floral scent and color may be not provide any nectar or food rewards, although it shares many traits closely associated with distinct pollinator species and foraging pre- for hawk moth-pollinated plants (Haber, 1984). The mass-flowering ferences. Previous studies have given rise to the hypothesis that white phenomenon not only occurred in Plumeria species with large in- color with aromatic compounds (benzenoids), particularly alcohols and fundibuliform flowers and tiny inflorescence bracts but also insome esters, were particularly preferred by nocturnal hawk moths (Majetic other families, such as, Araceae, Orchidaceae, and Scrophulariaceae et al., 2007, 2008; Raguso et al., 2003). More recent results showed that (Ackerman, 1986; Haber, 1984; Papadopulos et al., 2013). The specific flower color and scent are intrinsically coupled, and the evolutionary ∗ Corresponding author. Xuefu Rd, College of life science and technology, Honghe University, Mengzi, Yunnan, 661199, China. E-mail addresses: [email protected] (W.-C. Gong), [email protected] (S.-J. Xu), [email protected] (Y.-H. Liu), [email protected] (C.-M. Wang), [email protected] (K. Martin), [email protected] (L.-Z. Meng). 1 These authors contributed equally to this work. https://doi.org/10.1016/j.bse.2019.05.005 Received 9 February 2019; Received in revised form 2 May 2019; Accepted 11 May 2019 Available online 22 May 2019 0305-1978/ © 2019 Elsevier Ltd. All rights reserved. W.-C. Gong, et al. Biochemical Systematics and Ecology 85 (2019) 54–59 implications are complex (Bischoff et al., 2015; Policha et al., 2016). in a 10% sucrose solution. The scent-containing air was drawn through Therefore, intra-specific floral polymorphisms provide an opportu- glass cartridges containing adsorbent Porapak Q (150 mg, mesh 60/80; nity to interpret the distinctive selection behavior of pollination agents Waters Associates, Milford, MA, USA) for 2–3 h during daytime using a (Dormont et al., 2010; Gong et al., 2014). For example, hawk moth and pump with an outlet flow rate of 350 ml/min. The duration of trapping hummingbird pollinators impose divergent selection pressure on yellow activities depended on the relative strength of the scent to the common and red morphs of Mimulus (Scrophulariaceae) (Streisfeld and Kohn, feelings of the human nose. The ambient air pumped into the vacuum 2007). However, a change in flower color or a lack of flower color isa dryer was purified sufficiently with advanced activated carbon. To frequent and universal fact in wild populations, and it is also produced identify the background contamination of the chemical samples, am- in cultivated varieties or ornamental species by human domestication of bient air (purified air) was collected as a control. Due to marginal the species (Chang, 2016; Tooke and Battey, 2010). The diverse com- differences in flower size, ten flowers of each plant were collected binations of flower scent and color occur not only in natural popula- randomly and combined into one sample. Five to seven individual tions (Brown and Clegg, 1984; M. Eckhart et al., 2006; Waser and Price, plants of each form were used to obtain enough representative samples. 1981) but also in cultivated individuals through human hybridization Cartridges were conditioned before sampling by washing them with activities, whether deliberate or not. The high polymorphic floral traits 400 ml dichloromethane, n-hexane and acetone for 4 h. The adsorbed reflect genetic assemblage or phenotypic plasticity, and these leadto scent components were eluted with ca. 0.8 ml dichloromethane and the final population structures. were collected in a 1.5 ml Agilent vial (Agilent Corporation, USA). Many studies have emphasized the existence of variations in scent Then, the vials were stored in a −80 °C freezer until the final analysis components with distinct color morphs (Li et al., 2006; Majetic et al., was conducted. 2007; Odell et al., 1999; Salzmann and Schiestl, 2007). Color-scent The extracts were analyzed using coupled gas chromatography and relationships are complex and diverse, and they largely rely on shared mass spectrometry (GC-MS). In total, 17 samples were analyzed using biosynthetic pathways (Armbruster, 2002; Majetic et al., 2007). This an Agilent HP 6890 gas chromatograph (Agilent Technologies, Santa fact means that any mutation in a gene coding for an enzyme or a Clara, CA, USA) equipped with an HP-5MS column (30 m × 0.25 mm, regulatory element will have an impact both on color and scent emis- 0.25 μm film thickness), linked to an HP5973 mass spectrometer. sion. For example, Zuker et al. (2002) found that the suppression of a Helium (He) was used as a carrier gas at a flow of 1 ml/min, and the single key enzyme led to the formation of white-flowered mutants with injector temperature was set to 250 °C. The column temperature was higher amounts of aromatic compounds (methyl benzoate), suggesting first set at 40 °C and was then programmed to 250 °C at a rate of3°C/ that specific floral color-scent associations could be a consequence of min. Compounds were identified by comparing their retention times conserved biochemical pathways (Armbruster, 2002), and these asso- (RT) and mass spectra with those of authentic compounds or with MS ciations may not be dissociated, or formed, by natural or artificial se- spectra from the Wiley 7n.1 mass spectral library and the associated lection alone (Majetic et al., 2007). retention indices reported both in the NIST Chemistry Web Book In this study, we investigated color-scent associations in the three (http://webbook.nist.gov) and in the RI database 42 (Adams, 2001). forms of the floral polymorphic Plumeria rubra L. (Apocynaceae) ori- Kovats retention indices were calculated using the formula: ginating from Central America, showing three different distinct color I = 100 +100 × (t -t )/(t -t ) morphs. We analyzed the scent production of the three color forms of P. x n x n n+1 n rubra L. and attempted to determine whether the floral color and scent Where Ix is the retention index of the compound of interest, tx is the were associated in this species. We tried to address three questions: retention time of the compound of interest, tn and tn+1 are the retention times of heading and trailing n-alkanes, respectively, (Sigma-Aldrich (1) What is the scent composition difference among the three forms of Co., St. Louis, MI, USA), and n is the number of carbon atoms of heading P.