Abstract
A suitable internal standard for the measurement of natural xanthoxin (XAN) was developed. Endogenous XAN, abscisic acid (ABA),
phaseic acid (PA), dihydrophaseic acid (DPA), and epi-dihydrophaseic acid ( epi-DPA) concentrations were quantified in the pulp and seeds
of apples in various stages of fruit development. The relative amounts of ABA in the pulp increased toward fruit maturation. On a molar basis,
the amount of total XAN ( cis, trans-XAN and trans, trans-XAN) in immature fruit was equal to the amount of ABA. However during the
fruit ripening process, the total XAN levels markedly decreased in proportion with increases in the levels of ABA. At the climacteric rise and
postclimacteric stage ABA concentrations were higher than the total amount of XAN. The low levels of XAN in a ripening apple may be
caused by its rapid turnover. The total XAN concentrations was high in immature seeds but decreased toward seed maturation. The opposite
tendency was observed in the case of ABA concentration. Thus, decreases of total XAN correlated with increases in the ABA levels; this
tendency was observed in both the pulp and seeds, and was consistent with the role of XAN as an ABA precursor. In the pulp, PA concentrations
changed in a manner similar to those of ABA. The maximum epi-DPA concentration was 67% of the maximum ABA concentration, but the
maximum DPA concentration was only 11% of the maximum ABA concentration. Therefore, epi-DPA may be a major metabolite of PA in
the pulp. In contrast, DPA appeared to be the major metabolite of ABA in apple seeds, because the levels of DPA were higher than those of
PA and epi-DPA.
© 2003 Elsevier Ireland Ltd. All rights reserved.
Keywords:Abscisic acid; Dihydrophaseic acid;epi-Dihydrophaseic acid; Phaseic acid; Xanthoxin