3.4. The AZ formation is triggered by cold, as evidenced by the cytoplasmic streaming of AZ cortical cells
In the next year, we conducted an ex-vivo experiment to investigate whether cold stress contributes to the activation of early fruit abscission signalling. To determine the origin of early responsive signals, we selected the excised tree subunits consisting of young branch, pedicel, and a fruit from Hongro/M9 apple trees (Supporting Information Figure S3). After 1 week of incubation followed by 2 hr of cold shock at 4 °C, the AZ-containing pedicels were severely damaged compared with control (Figure 3a). We observed the AZ cortical cells by transmission electron microscopy and several vesicles were associated with the cytoplasmic streaming in cold-stressed group (Figure 3b), whereas only a few vesicles were detected in control (Figure 3c). Along with new vesicles detaching from the cell wall, the thickness of the cell wall was more irregular and variable in cold-stressed pedicel.