Abscisic acid activity across tissues: Linking biosynthesis, transport, and target-site action.

Abscisic acid (ABA) coordinates plant development and water-stress responses through mechanisms that extend beyond local biosynthesis and signaling. Increasing evidence indicates that ABA function depends on the spatial organization of hormone production, transport, catabolism, and perception across tissues. In this review, we highlight how ABA is synthesized mainly in vascular-associated cells and redistributed to distal target sites in leaves, roots, and seeds. We discuss recent findings showing that both ABA and its precursor, abscisic aldehyde, can move between tissues, thereby expanding the routes by which bioactive hormones accumulate. We further consider how transporters, tissue-specific sinks, and environmental cues shape ABA gradients, and highlight outstanding questions regarding the cellular pathways and regulatory mechanisms that determine ABA action in planta.