XVI International Botanical Congess

Aldehyde oxidase (AO) has been thought to catalyze the last step of ABA biosynthesis by oxidation of abscisic aldehyde (ABAld) to ABA. We have cloned four AO cDNAs (atAO-1, -2, -3 and -4) from Arabidopsis thaliana. Expression of atAO-3 mRNA was rapidly induced by dehydration of detached rosette leaves. It was known that endogenous ABA level was increased af ter dehydration of plants and thus atAO-3 product probably involves in ABA biosynthesis. In rosette leaves, we detected an AO activity having a substrate preference for ABAld. Experiments using antibodies raised against atAO-3 product and atAO-3 protein expressed in yeast (Pichia pastoris) revealed that atAO-3 encoded abscisic aldehyde oxidase.