Abscisic acid (ABA) is an important phytohormone regulating various
physiological aspects in plants such as seed maturation, dormancy, seedling growth,
and stomatal behaviour. In this chapter, a global picture with recent findings in ABA
metabolism and responses is overviewed. Because of putting the priority on simplicity,
to understand historical importance, you should refer to other reviews such
as Cutler et al. (Annu Rev Plant Biol 61:651–79, 2010). In recent years, many
enzymes responsible for the synthesis and catabolism of ABA have been identified,
almost completing the main pathway of ABA production. In ABA-responding cells,
there are sets of core components in the ABA reception system, which regulates
multiple responses including induction of gene expression and alteration of ion
transport. Many players modify the core components to produce sophisticated reactions.
The possibility of modifi cation of the pathways at the molecular level to
improve crop productivity will be discussed in the fi nal section.