The effect of abscisic acid and abscisic acid metabolites on the germination of cress seed

Abstract

Optical isomers of abscisic acid (ABA) and racemic mixtures of both abscisic acid and abscisic acid metabolites were studied to determine their effects on the emergence of root primordia and cotyledons from cress seed. The relative emergence sensitivity of cress seed to the racemic compounds was (±)-ABA aldehyde ≥ (±)-ABA alcohol > (±)-ABA > (±)7′-hydroxy ABA > (±)-phaseic acid. Thus ABA and ABA precursors were effective inhibitors whereas the ABA catabolites, phaseic acid, and 7′-hydroxy ABA had little or no effect on germination. The naturally occurring optically pure enantiomer (+)ABA was a more potent germination inhibitor than synthetic (−)-ABA. An ABA analog, 2′,3′-cis dihydro ABA (DHABA), that is not metabolized to phaseic acid was also studied for inhibitory activity. Although optically pure DHABA has the same configuration at C-1 as (+)-ABA, it was less inhibitory than (+)-ABA and its (−) enantiomer was inactive. The pattern of activity observed in treatments with the enantiomers of DHABA indicates that the configuration at C-1′ is important for maximum inhibition of cress seed germination. It also suggests that in contrast to monocot seeds, the formation of phaseic acid is not required for the inhibition of cress seed germination. Key words: abscisic acid, phaseic acid, ABA alcohol, ABA aldehyde, 7′OHABA, germination, ABA analogs.