Abstract
The catabolism of abscisic acid (ABA) through ABA 8'-hydroxyase (ABA8'ox) plays an important role in reducing ABA content in seed during imbibition, and thus in promoting germination. To investigate the effect of reduced ABA catabolism on germination in hexaploid wheat, we cloned three ABA8'ox homologues (named TaABA8'ox1A, TaABA8'ox1B, TaABA8'ox1D, respectively) and screened for mutations that lead to reduced ABA catabolism. In a screen for natural variation, one insertion mutation in TaABA8'ox1D, resulting in the change of the amino acid residues conserved between ABA8'oxs in plant, was identified in several Japanese cultivars. We employed one cultivar with TaABA8'ox1D mutation, "Tamaizumi", to produce a double mutant in TaABA8'oxls using a gamma-radiation treatment. In a screen for induced mutation, one deletion mutant lacking the entire TaABA8'ox1A, named 184G4, was identified. 184G4, a double mutant in TaABA8'ox1A/TaABA8'ox1D, showed a reduced expression of TaABA8'ox1s and an increased level of ABA content in the embryos during seed maturation and imbibition, and a reduced seed germination in comparison to "Tamaizumi", a single mutant in TaABA8'ox1D. These results indicated that the reduced ABA catabolism through the mutations in TaABA8'ox1s might have a positive effect on the inhibition of germination in wheat.
