Fig. 4.

Hypothetical model for fruitlet abscission under nutritional stress [according to Botton et al. (2011) and Eccher et al. (2013)]. The nutritional stress, enhancing the competition for assimilates between vegetative and reproductive sinks, is translated at both the fruit and seed levels through crosstalk between signalling pathways involving mainly sugars, ABA, and ethylene. Sugar signalling includes processes of sugar starvation, growth inhibition, sucrose accumulation, and trehalose-6-phosphate (T6P) signalling as described by Botton et al. (2011). In the fruit, the sugar signalling (through T6P) induces ABA and ethylene synthesis, which can increase ROS content and lead to an abscission signal. The abscission signal is then transmitted to the AZ, leading to fruit fall. When the seed perceives sugar depletion, a block of embryo development and cytokinin (CK) signalling occurs, leading to seed abortion. This crucial step would determine the depolarization of auxin transport, leading to the enhancement of AZ sensitivity to ethylene and its activation. The thickness of the arrows related to interorgan competition and storage partitioning is proportional to the strength of the organ as a sink.