Abstract
To facilitate elucidation of the functions of ABA and to find new mutants involved in ABA signaling, we developed a new inhibitor of ABA biosynthesis and named it abamine. Abamine was a potent competitive inhibitor of the double-bond cleavage enzyme of 9-cis-epoxycarotenoid dioxygenase, with a Ki of 38.8 microM. In 0.4 M mannitol solution, which mimics the effects of osmotic stress. abamine both inhibited stomatal closure in spinach leaves, which was restored by co-application of ABA, and increase in luminescence intensity in RD29B::LUC transgenic Arabidopsis. The ABA content of plants in 0.4 M mannitol was increased approximately 16-fold compared with controls, whereas 50 to 100 microM of abamine inhibited about 50% of this ABA accumulation in both spinach leaves and Arabidopsis. These results demonstrate that abamine is a novel ABA biosynthesis inhibitor targeting the oxidative cleavage of 9-cis-epoxycarotenoids, and it affects plant responses regulated by ABA.