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 9-cis-epoxycarotenoid dioxygenase (NCED), 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 increased luminescence intensity in RD29B::LUC transgenic Arabidopsis. Fifty to 100 microM of abamine inhibited about 50% of ABA accumulation in both spinach leaves and Arabidopsis in mannitol conndition. In addition, abamine also promoted germination at high temperatures in Arabidopsis, and enhanced radicle elongation in cress seeds. These results demonstrate that abamine is a novel specific ABA biosynthesis inhibitor targeting the oxidative cleavage of 9-cis-epoxycarotenoids, and it affects plant responses regulated by ABA.
