The 2009 ASHS Annual Conference

Abscission is a highly coordinated developmental process that results in shedding of organs at predetermined sites called abscission zones.  Abscission is often considered a stress response in plants, as it can be triggered by environmental, abiotic and pathogen-related challenges as well.  An accepted model of abscission identifies 4 major steps in the abscission pathway: 1) differentiation of the abscission zone, 2) competence to respond to abscission signals, 3) activation of abscission, and 4) post abscission transdifferentiation.  Step 1 is a major control point, and plants with fruit disrupted in their ability to form an abscission zone do not abscise. Competence of fruit to respond to abscission signals is developmentally regulated and influenced by environmental stimuli and cross talk between phytohormones such as auxin and ethylene. Activation of fruit abscission involves perception and transduction of signals that lead to downstream responses.  Increased gene expression of cell wall hydrolases and those involved in secondary metabolism, hormonal metabolism and the PR response occur as abscission advances. Final preparation for fruit separation and post abscission transdifferentiation may involve induction of genes and proteins whose activities may be associated with ongoing cell wall loosening processes and building a protective layer around the fractured surface of the abscised organ and the parent plant.  Examples of abscission control points in fruit and commercial implications of such control will be discussed.