2.1. Plant material and study sites
6-year-old ‘Hongro’ apple scions grafted onto ‘M9’ rootstocks (Hongro/M9) were grown under field conditions at the Apple Research Institute, Gunwi, South Korea. Young 3-cm sized fruit were collected together with the pedicel on 24th (37 days after full bloom, DAFB) of May 2018 for RNA-seq and metabolomics analyses. The following year, the tree subunits consisting of a branch, pedicel, and fruit were excised for ex-vivo cold shock experiment and put into a floral foam to prevent dehydration. These subunits were incubated at 25 °C for 168 hr after the 2 hr of initial cold shock treatment. To minimize any effects due to individual variations, we collected our samples from a single Hongro/M9 tree for experiments in both years. In May 2020, we collected tree subunits of Hongro/M9 apple trees at 42 DAFB for the secondex -vivo experiment. Subunits were divided into four groups by treatments as follows: Control (water); ABA (125 mg/L of ABA); Cold (initial cold shock at 4 °C for 2 hr); Cold + ABA (125 mg/L ABA followed by initial cold shock at 4 °C for 2 hr). All samples were incubated at 25 °C for 168 hr. The exogenous ABA treatment was applied onto the branch tissues connected to pedicel.