Abscisic-acid-deficient mutants at the aba gene locus of Arabidopsis thaliana are impaired in the epoxidation of zeaxanthin

Abstract. The xanthophyll content of wild type and abscisic acid (ABA) - deficient mutants of pea and Arabidopsis thaliana was determined. The wilty mutant of pea was indistinguishable from the non-mutant control. In contrast, plants homozygous for mutant alleles at the aba locus of Arabidopsis were very different from wild type. In these mutants, zeaxanthin accumulated to abnormally high levels. The major carotenoids, violaxanthin and 9'- cis -neoxanthin were virually absent from the mutant chromatograms. It was concluded that the aba genetic lesion impairs the epoxidation of zeaxanthin to violaxanthin and that this results in an inability to accumulate ABA. This provides clear evidence that zeaxanthin is a precursor of ABA.     

The Metabolism of cis ABA-aldehyde by the Wilty Mutants of Potato, Pea and Arabidopsis thaliana

RS-[²H₁] cis ABA-aldehyde was fed to ABA-deficient mutants ofpotato (droopy), pea (wilty) and Arabidopsis thaliana (aba¹)along with appropriate non-mutant controls. Both the wilty andaba¹ mutants readily oxidized the monodeuterated ABA-aldehydeto ABA. The incorporation of label into ABA by these two mutantswas indistinguishable from that detected in the non-mutant controls.In contrast, the droopy mutants poorly incorporated the labelledprecursor into ABA. Instead they reduced and isomerized RS-[²H₁] cis ABA-aldehyde to a mixture of 2, cis and 2, trans ABA-alcohols.Thus the droopy mutant affects the last step in ABA biosynthesis,a position it shares with the tomato mutants, flacca and sitiens.Genetic evidence suggesting that droopy and sitiens may be correspondinggene loci is discussed. Key words: ABA metabolism, wilty mutants, pea, potato, Arabidopsis