A Novel Inhibitor of 9-cis-Epoxycarotenoid Dioxygenase in Abscisic Acid Biosynthesis in Higher Plants

Abstract

Abscisic acid (ABA) is a major regulator in the adaptation of plants to environmental stresses, plant growth, and development. In higher plants, the ABA biosynthesis pathway involves the oxidative cleavage of 9-cis-epoxycarotenoids, which may be the key regulatory step in the pathway catalyzed by 9-cis-epoxycarotenoid dioxygenase (NCED). We developed a new inhibitor of ABA biosynthesis targeting NCED and named it abamine (ABA biosynthesis inhibitor with an amine moiety). Abamine is a competitive inhibitor of NCED, with a K i of 38.8 mM. In 0.4 M mannitol solution, which mimics the effects of osmotic stress, abamine both inhibited stomatal closure in spinach (Spinacia oleracea) leaves, which was restored by coapplication of ABA, and increased luminescence intensity in transgenic Arabidopsis containing the RD29B promoter-luciferase fusion. The ABA content of plants in 0.4 M mannitol was increased approximately 16-fold as compared with that of controls, whereas 50 to 100 mM abamine inhibited about 50% of this ABA accumulation in both spinach leaves and Arabidopsis. Abamine-treated Arabidopsis was more sensitive to drought stress and showed a significant decrease in drought tolerance than untreated Arabidopsis. These results suggest that abamine is a novel ABA biosynthesis inhibitor that targets the enzyme catalyzing oxidative cleavage of 9-cis-epoxycarotenoids. To test the effect of abamine on plants other than Arabidopsis, it was applied to cress (Lepidium sativum) plants. Abamine enhanced radicle elongation in cress seeds, which could be due to a decrease in the ABA content of abamine-treated plants. Thus, it is possible to think that abamine should enable us to elucidate the functions of ABA in cells or plants and to find new mutants involved in ABA signaling.

Abscisic acid (ABA)-mediated inhibition of seed germination involves a positive feedback regulation of ABA biosynthesis in Arachis hypogaea L.

“…This was associated morphogenetically with inhibited plumule apex growth and leaf primordium elongation ( Figures 3D and E), decreased number and length of axial and lateral buds and shorter length of compound leaves ( Figure 4D and E) during seed germination. Naproxen, the potent ABA biosynthesis inhibitor specifically targeting to NCED, is known to decrease endogenous ABA levels in higher plants (Han et al, 2004;Wan and Li, 2006). In the present study, we found that naproxen treatment decreased the levels of endogenous ABA ( Figure 2B) and AhNCED1 gene transcript ( Figure 2A) and concomitantly increased α-amylase activity ( Figure 2C), germination rate ( Figure 1C) and viability index ( Figure 1D) of germinating seeds.…”

“…The ABA-mediated inhibition of seed germination in peanut thus exhibited a dose-dependency ( Figures 1A and B). Naproxen, the potent ABA biosynthesis inhibitor specifically targeting to NCED (Han et al, 2004) increased the germination rate and viability index (Figures 1C and D). At day 2 and 6 after the onset of imbibition, the germination rate of germinating seeds treated with 0.5 mmol/l naproxen were respectively, 1.13 and 1.50 times as high as that of the control germinating seeds ( Figure 1C); accordingly, the viability index of seeds treated with 0.5 mmol/l naproxen was respectively, 1.35 and 1.92 times as much as that of control seeds ( Figure 1D).…”

“…In the present study, the effects of exogenous application of ABA and naproxen [a potent ABA biosynthesis inhibitor specifically targeting to NCED (Han et al, 2004)] on seed germination in peanut were investigated physiologically, biochemically and morphogenetically, with a view to gain further insight into the possible feedback regulation mechanism of ABA biosynthesis.…”

Abamine as a basis for new designs of regulators of strigolactone production

“…17) Abamine (ABM) is the first reported abscisic acid biosynthesis inhibitor that targets nine-cis-epoxycarotenoid dioxygenases (NCED), 12,13) and it has been suggested that abamine may also target other CCDs. 18) Interestingly, AbamineSG (ABMSG) was developed as an abscisic acid biosynthesis inhibitor based on the structural and functional characteristics of abamine, but was found to be a more specific and potent NCED inhibitor than abamine.…”

“…Abamine was synthesized using the method outlined by Han et al 12,13) GR24, a synthetic mimic of strigolactones, was synthesized as previously described. 14) In this study, GR24 with the same relative stereochemistry as (Ϯ)-strigol was used.…”