Figure 6. Proposed model for explaining differences in abscission between “first berries” and “late berries”.

Flowering is associated with IAA and ethylene content increase, so flowers that open first may have higher content of these hormones than unopened flowers. IAA activates polar auxin transport (PAT), as shown in many plant species, so we propose that flowers that will originate “late berries” may have lower PAT than flowers that will originate “first berries”, and as a consequence “late berries” may have higher ethylene sensitivity (Eth S), which is associated with the activation of ethylene responses, such as the abscission zone formation. “First berries” should be unaffected by ethylene since they have high PAT and this might explain why abscission rate is lower in “first berries” than in “late berries”, when they are compared at the same developmental stage (red outlined boxes).