PA analysis of leaf and root samples was carried out using liquid chromatography-tandem mass spectrometry (LC-MS/MS) following the procedure outlined in Kostenko et al. (2013). In brief, 5 mg of freeze-dried ground plant material was extracted with 0.5 ml 2% formic acid solution containing heliotrine (1 µg•ml-1) as internal standard. After centrifugation and filtration, 25 µl of the extracted filtrate was diluted with 975 µl of 10 mM ammonium hydroxide solution and 10 µl was injected in a Waters Acquity ultra-performance chromatographic system coupled to a Waters Quattro Premier tandem mass spectrometer (Waters, Milford, MA, USA). Separation and mass spectrometric detection of the PAs was as described in Cheng et al. (2011) and Appendix S2. Data were processed using Masslynx 4.1 software. ...