Hormone Synthetic Pathways and Genes in Arabidopsis: Abscisic acid

Abscisic acid (ABA: (S)-(+)-2-cis-ABA) was originally identified as the bioactive compounds that induce abscission or bud dormancy. However, contribution of ABA to these physiological responses has not been clearly demonstrated. Instead, studies using ABA-deficient mutants from several plant species revealed that this hormone is required for the induction and maintenance of seed dormancy, stomatal closure, and response to biotic and abiotic stresses. (R)-(-)-2-cis-ABA (generally termed (-)-ABA) is biologically active as an ABA analogue, but do not exist in plant tissues. (S)-(+)-2-trans-ABA (trans-ABA) has been detected from plant tissues but do not exhibit ABA activity. ABA is synthesized via carotenoids. The biosynthesis pathway after zeaxanthin formation is shown here.