ABA (Abscisic Acid) is a plant hormone that plays important role during many phases of the plant life cycle, including seed development and dormancy, embryo maturation, cell division and elongation, and in plant responses to various environmental stresses such as drought, salinity, cold, pathogen attack and UV radiation. However, despite the name, it does not appear to control Abscission directly; the presence of ABA in Abscising organs reflects its role in promoting senescence and/or stress responses, the processes preceding Abscission. ABA is a sesquiterpenoid (C15H20O4) with one asymmetric, optically active Carbon atom at C-1 f. The naturally occurring form is S-(+)-ABA; the side chain of ABA is by definition 2-cis,-4-trans. Trans, trans-ABA is biologically inactive, but R-(-)-ABA (a possible product of [...]