2.9 Determination of ABA, soluble sugar, and amino acid
The ABA extraction was performed using an early described method (Huoet al. , 2020) and measured using a liquid chromatography-mass spectrometry (LC-MS) system. The soluble sugar levels were measured according to Li et al. (2016). The amino acid content was determined based on Huo et al. (2020). The supernatant was filtered through a 0.22 μm organic filter for high-performance LC-MS analysis using the QTRAP5500 system (AB, America).