Agriculture Reference
In-Depth Information
Chapter 1
ABA and Its Derivatives: Chemistry
and Physiological Functions
Yasushi Todoroki
Abstract ABA, a sesquiterpene, is a small molecule that has a non-planar shape
and contains various functional groups. The C 15 ABA-skeleton is common in bio-
synthetic precursors (xanthoxin, abscisic alcohol, and abscisic aldehyde) and oxi-
dised catabolites (8′-hydroxy-ABA, phaseic acid, and dihydrophaseic acid). Thus,
the conformation of the molecule and its functional groups are the key factors
governing whether these ABA derivatives function as ABA mimics that can acti-
vate ABA receptors. Recent reports of the crystal structures of the ABA receptor
proteins, PYR/PYL/RCAR (PYL), give significant clues regarding the structural
requirements for eliciting ABA responses. The findings from structural studies of
PYL are generally consistent with those from structure-activity studies based on
bioassays using ABA analogues. The structural requirements for biosynthetic and
catabolic enzymes and for ABA transporters remain unknown, as these structures
have not yet been solved. However, ABA 8′-hydroxylases have been well inves-
tigated using in vitro enzyme assays. These studies show that different ABA-
binding proteins have somewhat different structural requirements. Based on this
knowledge, we can design a selective ligand that targets a specific ABA-binding
protein.
Keywords ABA · Derivatives · Functions · Structure requirements
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