Abstract.The xanthophyll content of wild type and abscisic acid (ABA) ‐ deficient mutants of pea andArabidopsis thalianawas determined. Thewiltymutant of pea was indistinguishable from the non‐mutant control. In contrast, plants homozygous for mutant alleles at theabalocus ofArabidopsiswere 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 theabagenetic 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 precurs