Measurement of MeJA concentration
MeJA profiling was carried out using reversed-phase chromatography on a Waters ultra-performance liquid chromatography (UPLC) system (Absciex 5500). As described in previous report (Mao et al., 2017; Kong et al., 2021), 700 μl of methanol was used to dissolve dried pellets of MeJA extracts. An Agilent Eclipse Plus C18 column (3.0 mm×100 mm×1.8 μm) was used for UPLC at 30 °C with a flow rate of 0.4 ml min–1. Gradient elution with solvent A (0.02 mM ammonium formate and 0.01% formic acid in water) and solvent B (0.02 mM ammonium formate and 0.01% formic acid in methanol) were used to separate the compounds, using the following elution profile: 0-1 min 60% A, 40% B; 1-8 min 60-5% A, 40-95% B; 8-10 min 5% A, 95% B; 10-10.1 min 5-60%A, 95-40% B; 10.1-12 min 60% A, 40% B.