Detection of programmed cell death in shoot tips during self-pruning process. TUNEL analysis was performed on 10-μm-thick bud meristem sections. (A) Vigorous spring shoots of shoot tips (Control); (B) staining signal of AZ at beginning of self-pruning; (C) staining signal of AZ after self-pruning; (E, F) staining signal of the AZ at the beginning of self-pruning; (H, I) staining signal of AZ after self-pruning; Number 1 and 2 (H) represents cells undergoing programmed cell death and dying cells, respectively. Red arrows represent AZ. Paraffin section bars are 100 μm.