| Osmanthus fragrans (Thunb.) Lour. is one of the top ten traditional flowers in China, which isan excellent ornamental species and a famous aromatic plant. O. fragrans can be classified intotwo kinds (blooming only in autumn and blooming many times during one year) according to thedifferent florescence. The kind blooming in autumn is further divided into three groups accordingto the flower color, which named Aurantiacus group, Albus group and Lutes group. In this species,the flower opening after flower bud differentiation is conducted by cold accumulated temperature.Associating with the temperature, most of cultivars always flower in October. In this period, thetemperature has great fluctuations that will significantly affect flower scent and flower color in O.fragrans. Among different cultivars especially with different flower color, the reflectance totemperature decrease or increase is varied, which determined by genetic mechanism andcontrolled by environment factors. Twenty-nine cultivars from the Aurantiacus, Albus, Lutes, andAsiaticus groups were used to identify the main flower scent and pigment components of O.fragrans. Meanwhile, to investigate the reflectance of flower scent and color in different cultivarsto temperature fluctuation, we set different treatments of high (32℃) and low (12℃and15℃)temperature according to natural conditions in recent years and analyze flower scent and colorunder different conditions by use of four cultivars from different groups.The main results were as follows:1: Comparative analysis of aromatic components in the main species of four groups of O.fragrans: Twenty-nine cultivars from the Aurantiacus, Albus, Lutes, and Asiaticus groups wereused as the experimental materials. Solid-phase microextractionand gas chromatography–massspectrometry methods were used to identify and analyze the aromatic components of O. fragrans.Cluster analysis was performed on these components to evaluate aroma. Alcohols and ketoneswere the principal types of compounds found in the four groups. Regardless of the relativecontents of aromatic components or the odor aroma values, no significant differences in the mainaroma components and characteristic aroma compounds were detected among the differentgroups. However, different species in the same group showed certain differences. In accord to therelative contents of aroma components, the main aromatic substances of O. fragransincludedcis-linalool oxide, trans-linalool oxide, linalool,2H-β-ionone, α-ionone, and β-ionone. Important aromatic substances, namely (Z)-ocimene, γ-decalactone, and geraniol, were also found.According to the odor aroma values of all substances, β-ionone, α-ionone, linalool, andtrans-linalool oxide were the common characteristic aroma substances among all species in thefour groups, and such substances contributed to the formation of the basic aroma of O. fragrans.The differences in some aroma substances and the combined effects of other substances causedthe variation in specific aroma among the species. For example, γ-decalactone and geraniolcaused the fruity aroma of most plants in the Lutes group. According to the cluster analysisresults and the information on the characteristic aroma components and aroma values, theanalyzed species can be divided into three fragrance types, namely, light sweet, rich, and elegant.Most of species in the Lutes group belonged to the first type, and most of the species in theAurantiacus, Albus and Asiaticus groups belonged to the latter two types. Aromatic substancesfrom plants of different sexes and from different geographic origins were not significantlydifferent and were not significantly related to the group.2. The emission of floral scent from O. fragrans. in response to temperature: The principaltypes of compounds and the characteristic aroma components of the O. fragrans.‘Yu Linglong’,‘Jin Qiugui’,‘Yan Honggui’ and ‘Yingye Dangui’ keep same under different temperatures, onlythe relative content have changed. When the temperature decreased (15,12℃), the relative contentof ionone (including α-and β-isomers) in ‘Yu Linglong’,‘Jin Qiugui’ and ‘Yingye Dangui’lessened whilet in ‘Yan Honggui’ it has increased at15℃. The relative content of linaloollessened in most samples except to ‘Yingye Dangui’; when the temperature increased (32℃), therelative content of ionone decreased in all samples. The relative content of linalool increased in‘Yu Linglong’ and ‘Yingye Dangui’, but lessened in ‘Jin Qiugui’ and ‘Yan Hongui’. The differentaroma values of linalool, α-ionone and β-ionone is the main reason for the variety flora scent offour species of O. fragrans. Compared with the natural conditions, the varieties and the content ofalkanes (C7-C30n-alkanes) increased with the increasing temperature, which may diluted theflora scent of O. fragrans. Since all the materials were treated in a long period (5-10d), the relativehigh or low levels of temperature will influenced the activity of the key biosynthetic enzymes, andfurther impact the biosynthesis of the main aroma components. The differenent geneticmechanisms will lead to the different sensitivity to temperature changes of O. fragrans, resultingin the different variation pattern of the characteristic aroma components. 3. Comparative analysis of flower pigment composition in the main species of four groups ofO. fragrans: The compositions of the pigment of twenty-three species of O. fragrans wereidentified and quantified using the technology of UV-visible absorption spectrometry,high-performance liquid chromatography with diode array detector (HPLC-DAD) andHPLC-electrospray ionization-mass spectrometry (HPLC-ESI-MS). The result indicates that therewere no carotenoids in Albus group, while α-or β-carotenoid in Aurantiacus and Asiaticus groups,and both α-and β-carotenoid in Lutes group. All the samples contained flavonoids. We haveobtained eight components of flavonoids that were detected in most of species, in which thestructure of four components have be confirmed, including to ethoxy quercetin,isorhamnetin-3-O-rutinoside, fomononetin-7-O-glucoside and syringetin-3-O-rutinoside thatbelong to flavonols, isoflavones and flavones, respectively. The isorhamnetin-3-O-rutinoside isthe main flavonol compound of O. fragrans for the highest content in all samples. The result ofprincipal component analysis showed that syringetin-3-O-rutinoside, P2, P3, P4and P5were alsothe principle components of the four groups in O. fragrans. while α-and β-carotenoid wereimportant in Aurantiacus and Lutes group. For Albus group, the compositions and content of theflavonoids have a decisive effect to its flora color, while in Aurantiacus, Lutes and Asiaticus groupthe compositions and content of carotenoids seems to be the major reason affecting the flroa clolorbecause the flavonoids always play a role of strengthening and enhancing if they co-exist withcarotenoids.4. The floral color of O. fragrans in response to temperature: Comparing the naturalcondition, the flora color of O. fragrans ‘Yu Linglong’,‘Jin Qiugui’,‘Yan Honggui’ and ‘YingyeDangui’ had a significant change in different temperatures. When the temperature was graduallydecreased (15and12℃), the flora colors of all the samples were deepen obviously, while thevalues of L*, A*, B*and C*were gradually decreased and h*value was increased. When thetemperature was enhanced (32℃), the flora colors of all samples were fade, while the values ofA*,B*and C*were gradually decreased and L*, h*values were increased. Under the relative lowtemperature condition (15and12℃), the contents of carotenoids in ‘Jin Qiugui’,‘Yan Honggui’and ‘Yingye Dangui’ were significantly increased, while in ‘Yu Linglong’, both the compositionsand contents were increased. The contents of flavonoids decreased obviously in all samples.Under the relative high temperature condition (32℃), there were nocarotenoids in O. fragrans. ‘Jin Qiugui’ and ‘Yu Linglong’, the compositions of carotenoids decreased in ‘Yingye Dangui’.The contents of carotenoids and flavonoids lessened in all samples. Principal component andmultiple regression analysis showed that isorhamnetin-3-O-rutinoside, syringetin-3-O-rutinoside,P3, P4, P5and α-and β-carotenoid were the most important pigment compositions relevant in floracolor of four species O. fragrans. Combining the change of the flora color with the contentandcomposition of flower pigment, carotenoids seems to be the principle factor for the change of floracolor in O. fragrans under different temperatures, and flavonoids mainly play a supporting role tostrengthen the flora color. |
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