2.4. ABA analysis
Seeds with a weight of 2 g were transferred to a mortar and ground into a powder before being mixed with 0.5 g sodium diethyldithiocarbamate and 20 mL 80% methanol. They were left to stand overnight in darkness. The next day, the solution was shaken using a vortex with 0.4 g polyvinyl pyrrolidone for 10 min, centrifuged at 3000 × g for 10 min and the supernatant was extracted with 10 mL 80% methanol twice. The combined solution was then vacuum concentrated (35 °C), extracted with ethyl acetate and filtered with a 0.22 μm membrane.
ABA was determined via the UPLC–MS/MS method. Liquid chromatography: Agilent 1260 Infinity; mass spectrometer: AB SCIEX QTRAP 5500; UPLC: Agilent SB-C18 column (4.6 mm × 50 mm, 1.8 μm particle size). The column temperature was 35 °C, flow rate was 0.8 mL min−1 and injection volume was 1 μL. The solvent system consisted of acetonitrile (A) and 0.1% acetic acid (B); MS: electro-spray ionization (negative mode) via multiple reaction monitoring (MRM) mode. The ion source temperature was 600 °C, ion source capillary voltage was 4500 V and the pressure of the nebulizer gas was 40 psi. Analyst version: 1.6.1. All the operations were performed according to the manufacturer's instructions.