Seasonal changes in metabolic profiles of galls and leaves of Rhus chinensis using gas chromatography mass spectrometry and liquid chromatography quadrupole time-of-flight mass spectrometry

Many researchers have studied the potential medicinal properties of galls from Rhus chinensis because of the importance of these galls in East Asian traditional medicine. Gall formation induced by a parasitic aphid species (Schlechtendalia chinensis) occurs via a well-documented developmental progression, and traditional medicinal efficacy is thought to be maximal during a specific portion of this cycle. To investigate seasonal changes of metabolites in the galls of R. chinensis, we collected samples from the galls and leaves of R. chinensis at sites in Mt. Jiri and Mt. Cheonma in Korea between May and December, 2011. Samples were extracted and analyzed gas chromatography mass spectrometry (GC-MS) and liquid chromatography quadrupole time-offlight mass spectrometry (LC-QTOF-MS) to monitor metabolic changes. Multivariate analyses such as principle components analysis (PCA) and orthogonal partial least square discriminant analysis (OPLS-DA) were used to find patterns in metabolite profile changes and the responsible substances for seasonal fluctuations. LC-QTOF-MS analyses showed differences of metabolites in same organisms depending on seasons, locations, and biological interactions. Additional GC-MS analyses identified approximately 28 metabolites including sugars, amino acids, and organic acids. Shikimic acid and gallic acid appear to be the major compounds contributing to the seasonal variability in metabolic profiles of R. chinensis leaves and galls. In addition, we found that shikimic acid and gallic acid content in R. chinensis galls were the highest during wintertime.