## 2 Results and Discussion
### Wounding-Induced Alterations in the SGs Content  
Six major iridoid compounds were initially quantified to assess wound-induced changes within the iridoid biosynthetic pathway--two iridoids (**1** and **2**) and four secoriidoids (**3**, **4**, **5**, and **6**). UHPLC/DAD/(+)HESI-MS2 analysis provided high-resolution identification of the iridoid compounds in samples and allowed for their quantification with high accuracy of both highly abundant compounds **4**, **5**, and **6**, and those present in much lower amounts (**1**, **2**, and **3**). The compounds were identified by their UHPLC retention times, UV/VIS, and MS spectra, and by the comparison with the standards and literature data. A UHPLC/DAD chromatogram at \(\lambda\) = 260 nm is presented in Figure 1, with extracted part of the chromatogram where iridoids are eluted. Quantification was performed using the SRM mode of the mass spectrometer (Figure S1), which utilized the two diagnostic fragments of each of the compounds, selected in a PIS (Product Ion Scanning) experiment (Table 1). The molecular ions of all the targeted compounds, except loganic acid (**1**), were visible in the negative ionization mode as adducts of acetic acid, which was present in the mobile phase (Figure S1, Table 1). The tendency of iridoids to form associated ion products-adducts is common [4; 45; 46]. Loganic acid (**1**), which eluted at \(\mathrm{Rt}\) = 2.01 min., displayed pseudomolecular ion [\(\mathrm{M}\)\(-\)H]\({}^{-}\) at \(m\)/z 375 and diagnostic MS2 fragments [\(\mathrm{M}\)\(-\)C\({}_{6}\)H\({}_{10}\)O\({}_{5}\)\(-\)H]\({}^{-}\) at \(m\)/z 213 corresponding to the loss of the hexose \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & & & \multicolumn{3}{c}{**UHPLC-MS Data**} & \multicolumn{3}{c}{**UHPLC-DAD Data**} \\ \hline
**Peak No.** & **Assignment** & \(\mathbf{t_{R}}\) **(min)** & **[\(\mathbf{M}\) + CH\({}_{3}\)COOH + HI\({}_{3}\)(m/z)]** & **SRM MS2 Fragments** & **cE (eV)** & \(\mathbf{t_{R}}\) **(min)** & \(\mathbf{\lambda_{max}}\) **[nm]** \\ \hline
**1** & **Loganic acid** & \(\mathbf{S}\)**,** & 2.01 & 375 & **213** (100), **168** (\(<\)5) & 20 & 1.95 & 240 \\
**5** & **Swertiamarin** & \(\mathbf{S}\)**,** & 2.61 & 433 & **179** (100); 161 (15) & 20 & 2.52 & 240 \\
**2** & **Loganic** & \(\mathbf{S}\)**,** & 2.88 & 449 & **227** (85); **127** (100) & 30 & 2.85 & 240 \\
**6** & **Gentiopicrin** & \(\mathbf{S}\)**,** & 2.90 & 415 & **179** (60); **119** (100) & 20 & 2.83 & 250,280, \\
**4** & **Sweroside** & \(\mathbf{S}\)**,** & 3.00 & 417 & **195** (100); **179** (85) & 20 & 2.94 & 250 \\
**3** & **Secologanin** & \(\mathbf{S}\)**,** & 3.66 & 447 & **155** (100); **123** (30) & 30 & 3.58 & 240 \\ \hline \hline \end{tabular}  
\({}^{\mathrm{S}}\) Confirmed using reference standards; R Confirmed according to the literature.  
\end{table} 
Table 1: Iridoids identified in methanol extracts of _Centaurium erythraea_ by Ultra-High Performance Liquid Chromatography/DAD/\(\pm\)HESI-MS2 (UHPLC/DAD/\(\pm\)HESI-MS2) analysis. Peak labels, retention times (\(\mathrm{t_{R}}\)), parent ions [\(\mathrm{M}\) + CH\({}_{3}\)COOH + HI\({}^{+}\)\(m\)/z, MS2 fragments used in an SRM (Single Reaction Monitoring) experiment, collision energies (cE), and \(\mathrm{\lambda_{max}}\) for each of the compounds are presented. moiety (-162 Da), and [M-C\({}_{6}\)H\({}_{10}\)O\({}_{5}\)-CH\({}_{2}\)O-H] at _m_/_z_ 168, which is in accordance with some previous studies [46]. Loganin (**2**) showed an acetic acid associated ion [M+CH\({}_{3}\)COOH-H]\({}^{-}\) at _m_/_z_ 449 and eluted at Rt = 2.88 min. It was possible to lose glucose and subsequently yield MS\({}^{2}\) ion [M-C\({}_{6}\)H\({}_{10}\)O\({}_{5}\)-H]\({}^{-}\) at _m_/_z_ 227, while another diagnostic fragment was [1,4F]\({}^{-}\) at _m_/_z_ 127 [4, 47]. Secologanin (**3**) with [M+CH\({}_{3}\)COOH-H]\({}^{-}\) at _m_/_z_ 447 eluted at Rt = 3.66 min.