2-Trans-Abscisic Acid Biosynthesis and Metabolism of ABA-Aldehyde and Xanthoxin in Wild Type and theabaMutant of Arabidopsis thaliana

Abstract
Abscisic acid (ABA) and 2-trans-ABA (t-ABA) biosynthesis were studied in wild type Landsberg erecta and the three allelic aba mutants of Arabidopsis thaliana (L.) Heynh., which are impaired in epoxy-carotenoid biosynthesis. Labelling experiments with 18O2and mass spectrometric analysis of [18O]ABA and its catabolites ABA-glucose ester (ABA-GE) and phaseic acid (PA), and t- ABA and t-ABA-GE, showed that t-ABA biosynthesis was less affected than ABA biosynthesis by mutations at the ABA locus. The aba-4 allele caused the most severe impairment of ABA biosynthesis compared with the other two mutant alleles aba-1 and aba-3, yet aba-4 plants synthesized as much t-ABA as wild type Landsberg erecta plants. Feeding experiments with RS- [2H6]ABA-aldehyde isomers and unlabelled xanthoxin isomers suggest that t-xanthoxin and t-ABA-aldehyde are precursors to ABA and t-ABA in Arabidopsis

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