*4.5. Quantification of Endogenous ABA*

About 100 mg of embryo from fresh seeds were extracted with 750 μL of methanol/water/acetic acid (80:19:1) and 10 ng/ ml of d6-ABA as internal standard, shaking for 16 h at 300 rpm in 4 ◦C. After centrifuging for 10 min at 13,000 rpm, the supernatant was transported to a new tube. The precipitate was re-extracted with 450 μL methanol/water/acetic acid (80:19:1) shaking for 4 h at 300 rpm in 4 ◦C. After centrifuging for 10 min at 13,000 rpm, the supernatant was combined with the previous one. The extracts were filtered with 22 μm filter membrane (Bizcomr, Nylon Syringe Filter, Guangzhou, China) and dried with N2. The residue was dissolved in 200μL of methanol and centrifuged for 15 min at 13,000 rpm under 4 ◦C. About 150 μL of supernatant were used for ultra-fast liquid chromatography (UFLC)/electrospray ionization/tandem mass spectrometry system (ESI/MS/MS) (Agilent 6520 QTOF, Hong Kong, China).
