The purpose of this study was first to investigate the possible roles of COR during cotton leaf abscission compared with using TDZ or water. In the present work, the phenotypic and anatomical changes in leaves, leaf detachment force, activity of Midazolam hydrochloride abscission-related enzymes, and expression of genes encoding the enzymes in different cotton tissues were determined under greenhouse and/or field conditions. We also estimated the transcript levels of two hydrolytic enzyme genes and one ethylene biosynthesis enzyme gene in leaf, petiole and leaf abscission zone as well as during leaf abscission. Finally, we determined boll opening, seedcotton yield and seed quality to elucidate whether and how COR affects cotton boll ripening and seed development. Appropriate and safe abscission chemicals will improve timing and facilitate harvest of cotton. In this study, we demonstrated that the phytotoxin, coronatine induced leaf abscission during cotton defoliation. Abscission occurs in an anatomically distinct cell layer known as the abscission zone. The abscission zone is defined as the region at base of abscising organs through which abscission eventually occurs. The anatomy of abscission is important for understanding the biology of a given plant species since form and structure comprise an appropriate starting point for potential functional comparisons between botanically distinct organs. Our data showed that abscission was accelerated when COR solution was applied to cotton leaves at 300 mg L21. Disassembly of cell walls in the AZ should lead to alteration in anatomical MRS 1220 structures in this separation layer. Leaf abscission zone cells were examined by scanning microscopy to elucidate the anatomic mechanisms of COR induced abscission in cotton leaves. After 14 d treatment with COR, the cells of AZ became elongated and disorganized, and the cell wall became thinner than that of control plants. It was also observed that COR alone could initiate the abscission process. The enlarged cells of the abscission zone seemed to have undergone a programmed cell death or physical dissolution in which the cells lost integrity. These results are consistent with a previous argument that while the abscission zone consists of several layers of cells across the petiole, the vascular bundles remain intact, allowing transportation of water and nutrients in and out of leaves. The COR treated leaf abscission zone showed a greater decrease in break strength than the control, suggested that the COR effect was over and above the wounding effect. Similar observations have been made in citrus fruit abscission zones in which the break strength decreased after COR treatment. The break strength under COR treatment was higher than that under TDZ treatment at 7 DAT, but not at 21 DAT. This suggests that leaf abscission induced by COR is relatively moderate, and could allow timely nutrient transport from cotton leaves to bolls.