Abscission research: what we know and what we still need to study

Purpose of the review: Abscission, organ separation, is an integral part of the life of a plant. Natural and artificial regulation of abscission can have substantive effects on crop yield and fruit quality. Here we present a brief overview of what we have learned about abscission in recent years as it relates to what we learned about abscission in previous decades, and also what we still need to study. Findings: It has been nearly 100 years since the discovery that ethylene played a role in abscission and more than 50 years since the discovery that auxin played a role. As more hormones were discovered – cytokinins, gibberellins, abscisic acid and jasmonic acid – each has been demonstrated to have at least some effect on the timing of abscission. Auxin is of particular interest because it plays a role in cell differentiation and competence to abscise as well as initiation and control of cell separation. Synthesis of a protective layer at the site of organ separation is common to most abscission processes but may be regulated separate from cell separation. Study of Arabidopsis floral organ abscission has stimulated many new lines of research including work on the signaling peptide Inflorescence Deficient in Abscission (IDA) and an abscission-specific change in cytoplasmic pH that correlates with the process of cell separation. Also, the finding that several genes associated with formation of organ boundaries in plant meristem are expressed in mature abscission zones may provide clues as to the differentiation of abscission zone cells.