The aba mutant of Arabidopsis thaliana is impaired in epoxy-carotenoid biosynthesis.

TLDR

Arabidopsis thaliana mutants with three aba alleles are deficient in the plant growth regulator abscisic acid (ABA). These mutants provide a model to investigate the physiological roles of epoxy‑carotenoids in photosynthesis. The study labeled ABA with 18O₂ in water‑stressed leaves of mutant and wild‑type plants to trace biosynthetic pathways. The aba mutants exhibit impaired ABA biosynthesis, reduced epoxy‑carotenoids violaxanthin and neoxanthin, accumulation of zeaxanthin, and evidence that ABA is produced by oxidative cleavage of epoxy‑carotenoids, while greening remains normal.

Abstract

The three mutant alleles of the ABA locus of Arabidopsis thaliana result in plants that are deficient in the plant growth regulator abscisic acid (ABA). We have used 18O2 to label ABA in water-stressed leaves of mutant and wild-type Arabidopsis. Analysis by selected ion monitoring and tandem mass spectrometry of [18O]ABA and its catabolites, phaseic acid and ABA-glucose ester (beta-D-glucopyranosyl abscisate), indicates that the aba genotypes are impaired in ABA biosynthesis and have a small ABA precursor pool of compounds that contain oxygens on the ring, presumably oxygenated carotenoids (xanthophylls). Quantitation of the carotenoids from mutant and wild-type leaves establishes that the aba alleles cause a deficiency of the epoxy-carotenoids violaxanthin and neoxanthin and an accumulation of their biosynthetic precursor, zeaxanthin. These results provide evidence that ABA is synthesized by oxidative cleavage of epoxy-carotenoids (the "indirect pathway"). Furthermore the carotenoid mutant we describe undergoes normal greening. Thus the aba alleles provide an opportunity to study the physiological roles of epoxy-carotenoids in photosynthesis in a higher plant.