Floral scent composition of Lilium sulphureum

Abstract

The genus Lilium (Liliaceae) comprises more than 100 species. Native Lilium species are spread over the Northern Hemisphere (10–60 ) and centered mainly in Asia, North America, and Europe [1, 2]. At present, lily is one of the most popular cut flowers in the world, and many modern lily cultivars originate from wild species. Lilium sulphureum Baker ex Hook.f. is endemic to the southern part of China, belonging to the trumpet section [1], whose flowers are funnelform, fragrant, and have big white tepals. Previous information on the floral scent of L. sulphureum or the trumpet section have not been found. Previous research have studied the floral scent of L. auratum (belonging to the oriental section) [3] and L. ‘Casa Blanca’ (an oriental lily hybrid) [4]. In the present study, we analyzed the floral scent composition and the day/night scent emission rhythm of L. sulphureum. Bulbs of L. sulphureum were collected from Sichuan Province and grown in the field in Xiaotangshan, Beijing. A complete open flower (2 days after anthesis) was sampled. Volatile compounds of an identical flowers were sampled in 09:00 and 21:00 in the field (21:30 was the peak of pollinator visitation in the field) [5]. Each experiment was replicated three times. Volatile compounds of L. sulphureum were adsorbed on Tenax GR and analyzed by GC-MS using a direct thermal desorption method. An automatic thermal desorber (ATD, Perkin–Elmer Turbo Matrix 650) was used to desorb the tubes at 260 C for 10 min. Helium flow was at a rate of 1.5 mL/min. The desorbed volatile compounds were first trapped in the cooled trap (–25 C); then the trap was quickly heated to 300 C at a rate of 40 C/s. Analytes desorbed in the ATD were injected into the GC through a capillary transfer line at 250 C; the sample amount was 4%. Analyses were performed using a Perkin–Elmer Clarus 600 gas chromatograph coupled to a Clarus 600T mass spectrometer. A DB-5MS fused-silica capillary column (30 m 0.25 mm 0.25 m) was employed. The GC oven temperature was programmed at 40 C for 2 min, then increased at 6 C/min to 180 C, 15°C /min to 270 C, and held for 3 min. The mass spectra was taken at 70 eV (in EI mode), and the mass scan range was m/z 30–500. TurboMass Ver 5.4.2 was used for analyses. The components were identified by matching the mass spectra with the NIST 08 library and confirmed by comparing the Kovats index (KI) with that in the database (Pherobase, www.pherobase.com/) [5]. Peak areas of the detected compounds were percent-normalized to calculate the relative amounts, and n-hexadecane was used as external standard in the semi-quantitative analysis. Composition of Floral Scent from L. sulphureum in the Night. There were 63 compounds detected, of which 46 compounds were identified from L. sulphureum floral scent, representing 99.5% of the total emission. The identified compounds were grouped by their biosynthetic pathways (Table 1) [6]. With respect to the number of compounds and emission amounts, monoterpenoids and benzenoids were the two major compound groups. Although L. sulphureum emitted many volatile compounds, only a few compounds attained percentages of more than 1% of the volatiles collected. Among these compounds, 1,8-cineole and methyl benzoate were the two most abundant compounds. Their relative amounts reached up to 46.8% and 36.9% respectively. Other compounds, such as -pinene (2.4%), sabinene (1.2%), limonene (1.5%), (E)-ocimene (4.7%), and -terpineol (2.4%), also played important roles. L. sulphureum also emitted indole (an N-containing compound) in trace amounts.