THE 7'-METHYL GROUP OF ABSCISIC-ACID IS CRITICAL FOR BIOLOGICAL-ACTIVITY IN WHEAT EMBRYO GERMINATION

Wheat (Triticum aestivum L.) embryo germination is inhibited by natura l (S)-(+)-abscisic acid (ABA). In this report we have determined criti cal structural features of the ABA molecule, particularly the methyl a nd ketone groups of the ABA ring, required for inhibitory activity. To examine the ring residues a series of new optically active ABA analog s have been synthesized in which the 4'-keto, 7'-, 8'-, or 8'- and 9'- carbons have been replaced with hydrogen atoms. Each of the analogs wa s tested over a range of concentrations as a germination inhibitor. En antiomers of the analogs altered at the 4'-keto or 8'- and 9'-methyl g roups were active, but less so than ABA. Both enantiomers of 7'-demeth ylABA were inactive as germination inhibitors. The results show that t he 7'-methyl group is absolutely required for activity, but that the o ther residues are less critical for hormone recognition.