Fig. 8. Model of abscission. BOP1 and BOP2 act early to promote the development of AZ specific anatomy of small cytoplasmically dense cell files in Arabidopsis. Later in flower development, a suite of enzymes involved in middle lamella degradation are expressed specifically in the AZ although with differing temporal patterns. Transcription of these enzymes is independent of BOP-driven formation of AZ anatomy. Abscission occurs following the expression of IDA in the AZ, which promotes cell separation. Expression of IDA is also driven independently from BOP1/2 activity.