Metabolites in the ABA biosynthetic pathway were identified by analyzi
ng xanthophyll profiles generated in embryos of wild-type and viviparo
us mutants of Zea mays L. The level of lutein differed greatly in vp8
embryos depending on whether or not elongated shoots were included in
the sample. Lutein was the major xanthophyll in embryos when elongated
shoots were included. However, lutein was a minor xanthophyll in vp8
embryos without elongated shoots and in wild-type embryos. Lutein Nas
produced mainly in the elongated shoots of viviparous mutants. No lute
in epoxides were detected in mutant or wild type embryos. These result
s show that lutein is not a precursor Of ABA in maize embryos. Accumul
ation of zeaxanthin combined with a reduction of epoxy-xanthophylls in
vp10 suggest that this defect impairs thr epoxidation of zeaxanthin.
Mutant vp-92EP8 accumulated all-trans-violaxanthin, while vp-92GN24 ac
cumulated all-trans-violaxanthin and all-trans-neoxanthin. These resul
ts imply that all-trans-neoxanthin is an intermediate between all-tran
s-violaxanthin and 9'-cis-neoxanthin. Under this model, vp-92EP8 preve
nts the conversion of all-trans-violaxanthin to all-trans-neoxanthin,
while vp-92GN24 prevents the conversion of all-trans-neoxanthin to 9'-
cis-neoxanthin. Accumulation of all-trans-violaxanthin, all-trans-neox
anthin and 9'-cis-neoxanthin combined with the reduction of zeaxanthin
was shown in vp8. A block in the oxidative cleavage step.