ABA Transport and Distribution in Relation to Its Function in Plants - Abscisic Acid: Metabolism, Transport and Signaling - page 59

Chapter 4
ABA Transport and Distribution in Relation
to Its Function in Plants

Bingbing Li and Wensuo Jia

Abstract Abscisic acid (ABA) is a phytohormone with key roles in various physi-
ological processes, including germination, stomatal movement, and biotic and
abiotic stress responses. Given that the sites of ABA biosynthesis and action are
separated in plant cells, ABA transport is an important step in ABA signaling.
ABA exhibits distinct patterns of compartmentalization, and its level in a specific
compartment is not only determined by its rate of biosynthesis and catabolism, but
also by the rates of ABA export and import. Compartmentalization ensures that the
physiology of the plant is not affected by ABA under normal conditions and that
redistribution of ABA in response to stress stimuli triggers ABA stress signaling.
ABA is transported between cells or tissues and also systemically in whole plants.
The expression of genes encoding key enzymes in the ABA biosynthesis pathway
in vascular tissues and the overlap in the expression patterns of genes encoding
enzymes involved in ABA biosynthesis and ABA transport implies the importance
of ABA transport, particularly ABA systemic transport, in ABA functioning. The
root-to-shoot transport of ABA further shows that ABA transport has critical roles
in plant systemic signaling, and the molecular identification and functional char-
acterization of ABA transporters provided direct evidence that ABA transport is
required for ABA signaling. The ion-trap mechanism by pH and ABA transporters
may operate synergistically, but in different manners, to control ABA transport and
distribution. Further investigations on ABA transport and localization will contrib-
ute to our understanding of mechanisms that modulate ABA signaling in plants.

Keywords ABA long-distance transport · ABA distribution · ABA function