# Headspace Volatiles and Endogenous Extracts of _Prunus mume_ Cultivars with Different Aroma Types
## 3 Discussion  
### The Similarities and Differences among the Components of Four Aroma Types  
The study showed that the main compounds of _P. mume_ cultivars from the four aroma types were phenylpropanoids/benzenoids, which is consistent with many ornamental plants, such as _M. iensis_[13], _Rosa odorata and R. chinensis_[24], _P. axillaris_[25], and _Luculia pinceana_[26]. Phenylpropanoids/benzenoids accounted for more than 90.57% of the total headspace volatiles and more than 87.71% of the total endogenous extracts. In this study, benzyl acetate, benzaldehyde, benzyl alcohol, and eugenol were used as the main headspace volatiles. In fact, benzyl acetate is also an important aromatic component of many ornamental plants [27; 28]. In addition, benzaldehyde was the most abundant \begin{table}
\begin{tabular}{c c c c c c} \hline
**Strong-Scented** & **Strong-Scented** & **Fresh-Scented** & **Fresh-Scented** & **Fresh-Scented** & **Sweet-Scented** \\
**vs.** & **vs.** & **Vs.** & **vs.** & **vs.** & **vs.** \\
**Light-Scented** & **Sweet-Scented** & **Light-Scented** & **Strong-Scented** & **Sweet-Scented** & **Light-Scented** \\ \hline tetracosanoic acid, & tetracosanoic acid, & & & & \\ methyl ester & & tetracosanal & & & \\ tetracosanal & 1-heptacosene & cinnamyl acetate & & & \\ phenylmethyl ester & & & & & \\ \multicolumn{1}{c}{} & & & & & \\ \multicolumn{1}{c}{} & & & & & \\ \end{tabular}
\end{table} 
Table 2: Endogenous biomarkers for the identification of _P. mume_ cultivars with four aroma types. Figure 5: Score plot of OPLS-DA models of endogenous extracts of _P. mume_ cultivars with the statistical parameters (R2X = 0.98, R2Y = 0.992, Q2 = 0.694). endogenous compound among the four aroma types, and the relative content ranges from 27.76 to 46.46%. Additionally, it is a volatile substance that can resist environmental stress in leaves [29]. It is also an important component in other plants, such as _P. axillaris_[3], _Syringa_[30], and _Bignonia nocturna_[31]. The content of endogenous extracts of the main components in the four aroma types was much higher than that of headspace volatiles; however, the volatilization rates of the four aroma types were different. Therefore, the volatilization of main components of different aroma types may be probably unrelated to the content of endogenous components. Previous studies have shown that volatile substances were transported through the plasma membrane and rely on active transportation. RNA interference down-regulates the _Petunia_ pharaonic transporter, which leads to the reduction in volatile matter release [32]. Therefore, the highly volatile components in _P. mume_ may be related to the transport mediated by transporters [33]. In addition, the volatilization rates of benzyl acetate were the highest in the four aroma types, which may be due to the higher volatility of ester products, while a variety of alcohols and aldehydes exist at the same time, are difficult to volatilize due to their high polarity. Many aromatic esters are synthesized from the aromatic alcohol and acyl donor catalyzed by the acyl-transferase. The rate of aromatic ester biosynthesis is limited not only by the activity of the enzyme responsible for the last step but also by the available substrates. Therefore, understanding the role of the substrate is the direction that needs to be focused on in the future. In addition, compared with previous studies on the floral scent of _P. mume_, this study focused on the differences between headspace volatiles and endogenous extracts among different aroma types and explored the differential components that contributed greatly to the formation of different aroma types, and the number of compounds detected components was higher than that previously described [8; 11; 18; 20; 21; 22]. Moreover, the in-depth study on the floral scents of different _P. mume_ cultivars provides a systematic basis for clarifying the mechanism of the floral scent of _P. mume_ cultivars.