| Abstract | We report here the synthesis and biological activity of a new persistent abscisic acid (ABA) analog, 8'-methylene ABA. This ABA analog has one additional carbon atom attached through a double bond to the 8'-carbon of the ABA molecule. (+)-8'-Methylene ABA is more active than the natural hormone (+)-ABA in inhibiting germination of cress seed and excised wheat embryos, in reducing growth of suspension-cultured corn cells, and in reducing transpiration in wheat seedlings. The (+)-8'-methylene analog is slightly weaker than (+)-ABA in increasing expression of ABA-inducible genes in transgenic tobacco, but is equally active in stimulating a transient elevation of the pH of the medium of corn cell cultures. In corn cells, both (+)-ABA and (+)-8'-methylene ABA are oxidized at the 8' position. ABA is oxidized to phaseic acid and (+)-8'-methylene ABA is converted more slowly to two isomeric epoxides. The alteration in the ABA structure causes the analog to be metabolized more slowly than ABA, resulting in longer-lasting and more effective biological activity relative to ABA. |
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