Determination of Volatile Organic Compounds and Endogenous Extracts and Study of Expression Patterns of TPS and BSMT in the Flowers of Seven Lilium Cultivars

Lily is one of the most important cut flowers in the world, with a rich floral fragrance. To further explore the fragrance emission mechanisms of lily cultivars, headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and organic solvent extraction-gas chromatography-mass spectrometry (OSE-GC-MS) were used to unveil the volatile organic compounds (VOCs) and endogenous extracts of seven lily cultivars. Furthermore, real-time quantitative PCR (qRT-PCR) was used to determine the expression levels of two key genes (TPS and BSMT) related to the biosynthesis of monoterpenoids and methyl benzoate. The results show that forty-five VOCs were detected in the petals of seven lily cultivars, and the main compounds were monoterpenoids and phenylpropanoids/benzenoids. Dichloromethane was the best solvent for extracting the endogenous extracts of Lilium 'Viviana' petals and eighteen endogenous extracts were detected using dichloromethane to extract the petals of seven lily cultivars. Each compound's emission ratio (natural logarithm of the ratio of VOC content to endogenous extract content) was calculated, and linear regression analyses between emission ratios and boiling points were conducted. Significant linear negative correlations existed between the emission ratios and boiling points of compounds, and the regression equations' coefficients of determination (R2) were all greater than 0.7. TPS was expressed highly in 'Viviana', 'Pink News', and 'Palazzo', and BSMT was expressed highly in 'Pink News' and 'Palazzo'. Correlation analyses between the gene expression levels and the monoterpenoids and methyl benzoate contents found that the TPS expression levels have strong positive correlations with monoterpenoids content, while no correlations were found between the expression levels of BSMT and the contents of methyl benzoate. This study lays the foundation for research on the release patterns of VOCs in the flowers of Lilium, and the breeding of lilies for their floral fragrance.

A Comparative Analysis of Floral Scent Compounds in Intraspecific Cultivars of Prunus mume with Different Corolla Colours

Prunus mume is the only fragrant flowering species of Prunus. According to the previous studies, benzyl acetate and eugenol dominate its floral scent. However, the diversity of its floral scents remains to be elucidated. In this work, the floral volatiles emitted from eight intraspecific cultivars of P. mume with white, pink and red flowers, were collected and analyzed using headspace solid-phase microextraction combined with gas chromatograms-mass spectrometry (HS-SPME-GC-MS). In total, 31 volatile compounds were identified, in which phenylpropanoids/benzenoids accounted for over 95% of the total emission amounts. Surprisingly, except for benzyl acetate and eugenol, several novel components, such as benzyl alcohol, cinnamyl acohol, cinnamy acetate, and benzyl benzoate were found in some cultivars. The composition of floral volatiles in cultivars with white flowers was similar, in which benzyl acetate was dominant, while within pink flowers, there were differences of floral volatile compositions. Principal component analysis (PCA) showed that the emissions of benzyl alcohol, cinnamyl alcohol, benzyl acetate, eugenol, cinnamyl acetate, and benzyl benzoate could make these intraspecific cultivars distinguishable from each other. Further, hierarchical cluster analysis indicated that cultivars with similar a category and amount of floral compounds were grouped together. Our findings lay a theoretical basis for fragrant plant breeding in P. mume.

Rethinking how volatiles are released from plant cells

For plant volatile organic compounds (VOCs) to be emitted, they must cross membrane(s), the aqueous cell wall, and sometimes the cuticle, before moving into the gas phase. It is presumed that VOC movement through each barrier occurs via passive diffusion. However, VOCs, which are primarily nonpolar compounds, will preferentially partition into membranes, making diffusion into aqueous compartments slow. Using Fick's first law, we calculated that to achieve observed VOC emission rates by diffusion alone would necessitate toxic VOC levels in membranes. Here, we propose that biological mechanisms, such as those involved in trafficking other hydrophobic compounds, must contribute to VOC emission. Such parallel biological pathways would lower barrier resistances and, thus, steady-state emission rates could be maintained with significantly reduced intramembrane VOC concentrations.