Violaxanthin Is an Abscisic Acid Precursor in Water-Stressed Dark-Grown Bean Leaves

Abstract

The leaves of dark-grown bean (Phaseolus vulgaris L.) seedlings accumulate considerably lower quantities of xanthophylls and carotenes than do leaves of light-grown seedlings, but they synthesize at least comparable amounts of abscisic acid (ABA) and its metabolites when water stressed. We observed a 1:1 relationship on a molar basis between the reduction in levels of violaxanthin, 9'-cis-neoxanthin, and 9-cis-violaxanthin and the accumulation of ABA, phaseic acid, and dihydrophaseic acid, when leaves from dark-grown plants were (10,12,15,20 one atom of 180 into the carboxyl group of ABA. One explanation for these latter results is that a preformed xanthophyll was cleaved by a dioxygenase to form an aldehyde that was converted to ABA by dehydrogenases. Li and Walton (12) suggested that at least a portion of ABA was derived from violaxanthin in water-stressed bean leaves based on studies in which the violaxanthin epoxide oxygens were labeled in situ with 180 via the xanthophyll cycle.One of the difficulties in demonstrating a precursor role for a major leaf xanthophyll is that these compounds are present at high levels in green leaves compared with the levels to which ABA and its metabolites accumulate even under water stress. Small differences in xanthophyll levels between leaf samples, either real or due to experimental error, can obscure any reductions that might result from ABA synthesis. Resynthesis of the precursors could also mask any reductions. Gamble and Mullet (7) stressed dark-grown fluridone-treated barley leaves which contained considerably lower xanthophyll levels than were present in untreated green leaves. They observed that ABA production was still 25% of normal, even when xanthophyll levels had been reduced by 99%. They also reported that violaxanthin, neoxanthin, and antheraxanthin levels were reduced during the stress period. Their results were confounded, however, by the fact that xanthophyll levels were also reduced, albeit to a lesser extent, when leaves were detached but not stressed. Thus, they were unable to conclude what the stoichiometry was between xanthophyll reduction and total ABA synthesis. We report on the results we have obtained with bean leaves stressed after detachment from dark-grown bean seedlings. In this system, only leaves that have been stressed show significant changes in xanthophyll content, the levels of ABA produced are at least comparable to those in light-grown plants, and the total amount of ABA produced is closely matched by reductions in the levels of several xanthophylls. These results enable us to draw inferences about the origin of ABA. MATERIALS AND METHODS Plant MaterialsPhaseolus vulgaris L. cv Blue Lake seeds were surfacesterilized with a 10% Clorox solution for 30 min and then imbibed in sterile water for 7 h. The seeds were planted in flats in a soil:vermiculite mixture (1:1) and grown in complete darkness at about 23°C for 8 or 9 d. Unless otherwise indicated, plants were sprayed with fluridone (13 mg L-') twice daily from d 4 to the end o...

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

“…cis-Carotenoid isomers were characterized by rechromatography of iodine-treated trans-carotenoid isomers and by spectrophotometric analysis and predicted equilibrium stoichiometries (26,27). In addition, the identities of violaxanthin, neoxanthin, and antheraxanthin isomers were confirmed by their retention times in reverse-phase HPLC systems (16,17).…”

“…(v) A 1:1 molar correlation between decreases in trans-violaxanthin and 9'-cis-neoxanthin (Fig. 1) levels and concomitant increases in ABA and its catabolites has been shown for dark-grown water-stressed bean leaves (16,17). In contrast to higher plants, phytopathogenic fungi synthesize ABA by a direct pathway from farnesyl pyrophosphate (18, 19).…”

A Novel Inhibitor of 9-cis-Epoxycarotenoid Dioxygenase in Abscisic Acid Biosynthesis in Higher Plants

“…Unlike other plant hormones, the endogenous concentration of ABA increases more than 10-fold within a few hours of drought stress and decreases dramatically to normal levels following rehydration (Zeevaart, 1980). Much evidence indicates that in higher plants ABA is synthesized via oxidative cleavage of epoxycarotenoids (Zeevaart and Creelman, 1988;Li and Walton, 1990;Parry et al, 1990). A number of steps may be regulated in the ABA biosynthesis pathway in higher plants, but special interest has focused on the enzyme involved in the oxidative cleavage of 9-cis-epoxycarotenoids, which is the key regulatory step in ABA biosynthesis in response to environmental stresses ( Fig.…”

Xanthophyll biosynthesis in chromoplasts: isolation and molecular cloning of an enzyme catalyzing the conversion of 5,6‐epoxycarotenoid into ketocarotenoid

“…Much less is known about the later steps of the plant carotenogenic pathway which involve the synthesis of xanthophylls. Several lines of evidence (Cholnoky et aL, 1955(Cholnoky et aL, , 1956Davies et aL, 1970;Neamtu and Bodea, 1969;Neamtu et a1.,1969;Valadon and Mummery, 1977) suggest that epoxyxanthophylls are reactive intermediates involved in the enzymic interconversion of carotenoids (Camara, 1980a(Camara, , 1980bMon~ger, 1980, 1981 ;Costes et aL, 1979) as part of the xanthophyll cycle (Yamamoto, 1979;Yamamoto and Higashi, 1978) and even in the formation of abscisic acid and related derivatives (Li and Walton, 1990;Rock and Zeevart, 1991). However, little is known about the enzymology of xanthophyll biogenesis.…”