Abstract
Regulation of ABA biosynthesis is crucial for plant's adaptive responses to osmotic stresses. Arabidopsis 9-cis-epoxycarotenoid dioxygenase 3 (AtNCED3) is known to be the rate-limiting enzyme in ABA biosynthesis under drought stress conditions. However, regulatory mechanisms underlying drought induction of NCED3 is still unknown. In the present study, we investigated the expression and localization of AtNCED3, AtABA2 and AAO3 in turgid and dehydrated plants using specific antibodies against each enzyme. Western blotting showed that AtABA2 and AAO3 were expressed in turgid plants, whereas AtNCED3 was undetectable. Induction of AtNCED3 was observed in rosette leaves after 30 min of dehydration. The expression patterns of ABA biosynthetic enzymes were investigated by an immunohistochemical technique. In dehydrated leaves, the immunofluorescent signal for AtNCED3 was observed in vascular bundles. In addition, AtABA2 and AAO3 were also localized in the identical tissues. These results indicate that drought induced ABA production occurs in vascular systems.
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