Repression of alpha-amylase activity by anoxia in grains of barley is independent of ethanol toxicity or action of abscisic acid

We studied the effects of anoxia on alpha-amylase induction, comparing rice (Oryza sativa L.) and barley (Hordeum vulgare L.) grains. While gibberellic acid (GA(3)) induces alpha-amylase in rice half-grains under either aerobic or anaerobic conditions, barley half-grains are insensitive to this hormone when applied under anoxia. The possible repressive role of ethanol and abscisic acid (ABA) was investigated. Exogenously added ethanol at concentrations mirroring those found in anaerobically treated tissues was unable to repress alpha-amylase. The level of ABA in anoxic tissues was found to be much lower than the threshold for alpha-amylase repression. overall, the results indicated that these two compounds cannot be held responsible for the failure of barley grains to respond to gibberellic acid. Furthermore, anoxia repressed the induction of alpha-amylase downstream of the slender mutation, indicating that the repression is independent of effects related to gibberellin perception. Overall, the results suggested that the ability of rice to respond to gibberellins under anoxia is an adaptative trait, independent of known negative regulators of alpha-amylase induction.