The biological and structural similarity between lunularic acid and abscisic acid.

Lunularic acid (LA) inhibited not only the germination and the growth of cress and lettuce at 1 mM but also the gibberellic acid (GA3)-induced alpha-amylase induction in embryoless barley seeds at 120 microM, which was recognized as a specific activity of abscisic acid (ABA). Moreover LA and ABA equally inhibited the growth of Lunularia cruciata A18 strain callus at 40 and 120 microM. A computational analysis revealed that the stable conformers of LA could be superimposed on the stable ABA conformers. In addition, the antibody raised against the conjugate of C1-ABA-bovine serum albumin (ABA-BSA) reacted with LA-horse-radish peroxidase (LA-HRP) conjugate as well as ABA-HRP conjugate, apparently. These results can explain why LA has ABA-like activity in higher plants. Moreover the results suggest that LA and ABA bind to the same receptor in higher plants.