ABA Transport and Plant Water Stress Responses.

To understand the integrative networks of signaling molecules, the sites of their biosynthesis and action must be clarified, particularly for phytohormones such as abscisic acid (ABA). The relationship between the sites of ABA biosynthesis and transport has been discussed extensively in the context of guard cells and stomatal regulation. However, guard cells are not the only site of ABA action. Recent studies have reported multiple sites of ABA biosynthesis and multiple ABA transporters, indicating that ABA transport regulation is not unidirectional but rather forms complex networks. Therefore, it is important to determine how multiple ABA sources coordinately contribute to individual biological processes under various physiological conditions.