Submitted to: Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/10/1997
Publication Date: N/A
Citation: Interpretive Summary: The plant hormone ABA (abscisic acid) can reduce preharvest sprouting in wheat, which lowers grain quality. ABA can also stimulate cold temperature and drought acclimation in plants, which reduced winterkill and drought damage. However, the beneficial effects of ABA are short-lived because ABA is readily metabolized in plants. We report here the synthesis of an altered form of the ABA molecule (called an ABA analog) that is metabolized more slowly than ABA. We show that this new persistent ABA analog is longer lasting and has more effective activity than ABA for a range of biological responses in wheat and corn. For example, we show that the persistent ABA analog is 5 to 10 times more effective than ABA in blocking wheat embryo germination. This discovery of an ABA analog that is longer lasting than the natural hormone ABA provides a way to maintain physiological responses involving ABA in plants. Use of the persistent ABA analog will help scientists to better identify the initial molecular and biochemical responses regulated by ABA. This longer-lasting ABA analog will also now be tested for practical agricultural purposes aimed at reducing losses due to sprouting, winterkill and drought.
Technical Abstract: We report here the synthesis and biological activity of a new persistent abscisic acid 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, reducing growth of 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 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, reulting in longer lasting and more effective biological activity relative to ABA.