Analysis of Spatiotemporal Changes in Jasmonic Acid, Salicylic Acid, and Indole-3-Acetic Acid in Tea Plants Based on Silylation and Gas Chromatography-Mass Spectrometry

Phytohormones play a vital role in plant responses to biotic stresses. Although phytohormone determination mainly employs ultra-high-performance liquid chromatography–tandem mass spectrometry (UHPLC-MS/MS), its high costs and technical requirements limit utility, whereas gas chromatography–mass spectrometry (GC-MS) is more widely used. To determine jasmonic acid (JA), salicylic acid (SA), and indole-3-acetic acid (IAA) in tea plants, a GC-MS method was developed, including selection of silylating reagents and establishment of metabolism quenching and purification methods. SA, JA, and IAA contents in tea leaves increased significantly after storage at −80 °C or extraction at room temperature. These increases were prevented by immersing samples in a 95 °C water bath. Quantification limits for SA, JA, and IAA were 0.020 ng mg−1, 0.015 ng g−1, and 0.015 ng g−1, similar to or exceeding those obtained by UHPLC-MS/MS. Recoveries and RSD were 93.1–98.9% and 2.1–9.9%, respectively. Only 10 mg of tea leaves was sufficient for simultaneous analysis of the three phytohormones. The JA response to geometrids was strong compared with the SA response, whereas the opposite trend was observed for leafhoppers. The systemic responses of JA and SA were rapid, similar to the local response. These results indicate that the proposed method is sensitive and reliable.