## 3 Discussion  
Floral scents always vary among different ornamental species or cultivars. Both the composition and the amount of the volatiles determine the specific flower fragrance [19]. The number of volatiles emitted from _P. mume_ is less than other species, such as bearded iris (219) [10], _Lithophragma_ (132) [20], _G. sempervirens_ (81) [8], but approximate to _Lilium_[6], _P. mume_ hybrids, and _Cymbidium_[21]. Comprehensive analysis of the floral scent profiles indicates that the fragrance may be not straightly connected with the number of compositions but their concentration. The number of components changes slightly from weak-scented 'Wuy' to heavy-scented 'Zao'. Similar phenomenon occurs in _Camellia_ that about 30 volatiles were identified in _C. macrospenia_ (weak-scented) and _C. buxifolia_ (moderate-scented) [4]. The VOCs are also different among intraspecific or interspecific cultivars. In our work, 31 compounds were identified, predominant with aromatic benzenoids and phenylpropanoids, including benzyl alcohol, benzyl acetate, cinnamyl alcohol, cinnamyl acetate and eugenol. Compared to the preliminary study [14], benzyl acetate and eugenol are the major component in several cultivars indeed. Differently, emission amount of benzyl alcohol in the investigated 'Jia' is far more than that in other flowers of _P. mume_ cultivars. In addition, cinnamyl alcohol and cinnamyl acetate are novel compounds released from _P. mume_. As shown in our analytical data, benzyl acetate, eugenol, benzyl alcohol and cinnamyl acetate contribute to the floral scents of _P. mume_. Interaction of various VOCs forms the floral aroma that is characterized by a component with a higher odor value (content/olfactory threshold) [22]. Benzyl acetate is an important aromatic component of ripe fruits and perfumes in many ornamental plants, such as Myrtaceae fruit crops [23], _Jasminum sambac_[24], _Zygopetalum m micalutum_[25]. Similarly, the floral scents in four of the eight cultivars, including strong-scented 'Zao' and 'Zah' and moderate-scented 'Sub' and 'Fub', are dominated by large amounts of benzyl acetate with fruit and jasmine aroma [26]. The cinnamon-fruity aroma of strong-scented 'Fenp' is decided by cinnamyl acetate. And floral odor with sweet-flowery-fruity of moderate-scented 'Fenh' is characterized by the interaction of benzyl acetate and cinnamyl acetate. Figure 4: Heatmap of core VOCs and hierarchical cluster analysis of eight _P. mume_ cultivars. The colour of the heatmap ranges from dark blue (value, -3.0) to brown (value, 3.3) in the natural logarithmic scale. Data are presented with means of biological replicates. The emission values were normalized by log\({}_{10}\) transformation. Floral aroma of 'Jia' is provided by benzyl alcohol and eugenol. The light scented 'Wuy' is characterized by eugenol with a spicy clove odor. The high diversity of floral volatiles provides rich germplasm for developing new cultivars with diverse fragrance. Through comprehensive analysis of the floral volatile compositions in the eight intraspecific cultivars, we conclude that the components of white flowers were similar but different in pink flowers. In white flowers, benzyl acetate and eugenol function as main components. While benzyl acetate, cinnamyl acetate and benzyl alcohol play important roles in the floral aroma of pink flowers. This result inspires us to further investigate about the complex molecular mechanism in our future study. The synthesis of floral VOCs is mainly regulated by the expression of related genes, enzyme activity and substrate availability involved in the biosynthesis pathways. Our results indicate that benzenoids, especially aromatic esters, are the predominant components contributing to the unique aroma of _P. mume_ cultivars. Similarly, the floral fragrance of many plants is dominated by aromatic esters, which are synthesized from the aromatic alcohol and acyl donor catalyzed with the acyltransferase.