Metabolite extraction
Leaf samples (0.5 g) were ground in a pre-chilled mortar. The powder was extracted with 50% methanol buffer at room temperature for 10 min followed by storing overnight at -20°C. After centrifugation at 4,000 g for 20 min, the supernatants were transferred into new 96-well plates. The samples were stored at -80°C prior to the liquid chromatograph-mass spectrometer (LC-MS) analysis. In addition, pooled quality control (QC) samples were also prepared by combining 10 μL of each extraction mixture.