8'-METHYLENE ABSCISIC-ACID - AN EFFECTIVE AND PERSISTENT ANALOG OF ABSCISIC-ACID

We report here the synthesis and biological activity of a new persiste nt abscisic acid (ABA) analog, 8'-methylene ABA. This ABA analog has o ne additional carbon atom attached through a double bond to the 8'-car bon of the ABA molecule. (+)-8'-Methylene ABA is more active than the natural hormone (+)-ABA in inhibiting germination of cress seed and ex cised wheat embryos, in reducing growth of suspension-cultured corn ce lls, and in reducing transpiration in wheat seedlings. The (+)-8'-meth ylene 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 cel l cultures. In corn cells, both (C)-ABA and (+)-8'-methylene ABA are o xidized at the 8' position. ABA is oxidized to phaseic acid and (+)-8' methylene ABA is converted more slowly to two isomeric epoxides; The a lteration in the ABA structure causes the analog to be metabolized mor e slowly than ABA, resulting in longer-lasting and more effective biol ogical activity relative to ABA.