## 2 Results  
### Analysis of terpenoids in Stevia  
To investigate terpenoids produced by Stevia tissues, we extracted volatiles from leaves, flowers, stems, and roots and analyzed them by Gas Chromatography-Mass Spectrometry (GC-MS). Figure 1, Supplementary Figure S1, and Table 1 show qualitative and quantitative variation in the composition of VOCs in the four tissues. Flowers and roots produced 36 compounds each, whereas stems and leaves produced a total of 34 and 23 compounds, respectively. Among all tissues, flowers had the highest number of VOCs, followed by leaves and roots, with stems producing the least quantity (Supplementary Figure S1). Among the putatively identified VOCs, terpenoids were the predominant class of volatiles in all four tissues and contributed more than 90% to total VOCs' composition. Among terpenoids, diterpenoids were mainly found in leaves and flowers, whereas sesquiterpenoids dominated the volatile compositions of stems and roots (Figure 1B). Stevia flowers produced large quantities of labdane-type diterpenoids, such as copalic acid, copaiferic acid, and 8(17), 12-labda-diene-15,16-dial (Figure 1 and Table 1). Even though copalic acid and copaiferic acid were detected in leaves, the levels were lower than those of flowers. Unlike flowers and leaves, stems, and roots accumulated several sesqui-, accounting for more than 80% of total VOCs (Figure 1B, Table 1). \(\beta\)-farnesene was the most abundant compound produced by stems (52.53%), whereas roots possessed large quantities of himachalol (21.00%), \(\beta\)-sesquiphellandrene (15.91%), \(\alpha\)/\(\beta\)-isocompene (14.90%), and \(\alpha\)-longipinene (3.18%) (Figure 1A and Table 1).  
Figure 1: Volatile organic compounds (VOCs) of Stevia tissues. (**A**) Photographs of Stevia leaves, flowers, stems, and roots and their VOCs’ emission profile shown by gas chromatogram. The arrows indicate the internal standard camphor. Peaks numbers are identical to those listed in Table 1. TIC, Total ion chromatogram. (**B**) Classification of Stevia VOCs. Data are the mean \(\pm\) standard deviation of three readings.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**No. \({}^{\star}\)**} & \multirow{2}{*}{**Compound Name**} & \multirow{2}{*}{**RT \({}^{\star}\)b**} & \multirow{2}{*}{**RI \({}^{\star}\)c**} & \multicolumn{3}{c}{**Molecular**} & \multicolumn{3}{c}{**RA (\%) \({}^{\ddagger}\)**} \\ \cline{5-9}  & & & & **Formula** & **L** & **F** & **S** & **R** \\ \hline
1 & p-Xylene & 8.17 & 886 & C\({}_{4}\)H\({}_{10}\) & 1.10 & 0.29 & 0.20 \\
2 & \(\alpha\)-Pinen & 9.18 & 962 & C\({}_{50}\)H\({}_{16}\) & 0.27 & 0.51 & 0.28 & \\
3 & \(\beta\)-Phellandrene & 9.81 & 1009 & C\({}_{50}\)H\({}_{16}\) & 0.28 & 0.35 & 0.19 & \\
4 & \(\beta\)-Pinen & 9.97 & 1021 & C\({}_{50}\)H\({}_{16}\) & 3.52 & 5.73 & 3.59 & \\
5 & \(\alpha\)-Teripolene & 10.27 & 1044 & C\({}_{50}\)H\({}_{16}\) & & & 1.81 & \\
6 & \(\alpha\)-Phellandrene & 10.34 & 1049 & C\({}_{50}\)H\({}_{16}\) & & & 0.82 \\
7 & \(\beta\)-Cyrene & 10.68 & 1074 & C\({}_{50}\)H\({}_{16}\) & & & 0.26 \\
8 & DS/Siveness & 10.76 & 1080 & C\({}_  
Of the 60 terpenoids identified, only three sesquiterpenoids (\(\beta\)-caryophyllene, \(\alpha\)-caryophyllene, and bicyclogermacrene) were found in all four tissues, where they showed variation in quantities (Table 1). In addition, we observed tissue-specificity in the production of a few terpenoids. For instance, \(\alpha\)-terpeniol, \(\alpha\)-bergamotol, \(\gamma\)-bisabolene, and \(\beta\)-caryophyllene oxide could only be detected in stems, while limonene was found only in flowers. Interestingly, out of 30 terpen produced by Stevia roots, 18 were found only in roots. Tissue-specific emission of these terpen might be essential for the interaction of roots with beneficial soil microbes and/or for the protection of roots from pathogens (Table 1).