Optically Pure Abscisic Acid Analogs—Tools for Relating Germination Inhibition and Gene Expression in Wheat Embryos

We report an examination of the structural requirements of the abscisic acid (ABA) recognition response in wheat dormant seed embryos using optically pure isomers of ABA analogs. These compounds include permutations to the ABA structure with either an acetylene or a trans bond at C-4 C-5, and either a single or double bond at the C-2' C-3' double bond. (R)-ABA and the three isomers with the same configuration at C-1' as natural ABA were found to be effective germination inhibitors. The biologically active ABA analogs exhibited differential effects on ABA-responsive gene expression. All the ABA analogs that inhibited germination induced two ABA-responsive genes, wheat group 3 lea and dhn (rab). However, (R)-ABA and (S)-dihydroABA were less effective in inducing the ABA-responsive gene Em within the time that embryonic germination was inhibited.