Control of abscisic acid synthesis

The abscisic acid (ABA) biosynthetic pathway involves the formation of a 9- cis-epoxycarotenoid precursor. Oxidative cleavage then results in the forma tion of xanthoxin, which is subsequently converted to ABA, A number of step s in the pathway may control ABA synthesis, but particular attention has be en given to the enzyme involved in the oxidative cleavage reaction, i.e. 9- cis-epoxycarotenoid dioxygenase (NCED), Cloning of a gene encoding this enz yme in maize was first reported in 1997, Mapping and DNA sequencing studies indicated that a wilty tomato mutant was due to a deletion in the gene enc oding an enzyme with a very similar amino acid sequence to this maize NCED, The potential use of this gene in altering ABA content will be discussed t ogether with other genes encoding ABA biosynthetic enzymes.