Metabolomic profiling
Metabolomic profiling was conducted using a LC-ESI-MS/MS system (HPLC, UFLC SHIMADZU CBM30A system; MS, Applied Biosystems 6500 Q TRAP). Chromatographic separation was performed on an ACQUITY UPLC HSS T3 C18 column (2.1 mm X 100 mm X 1.8 μm; Waters) using a mobile phase A of 0.04% acetic acid in deionized water and mobile phase B of 0.04% acetic acid in acetonitrile with flow rate 0.4 mL min-1. The fold-change for each metabolite was calculated as the ratio of the amount in stress-treated plants relative to that in control plants. According to the statistically significant threshold (P <0.05) and variable influence on projection (VIP) values (VIP>1.0), differential metabolites were selected.