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Abstract: We studied the effects of anoxia on α‐amylase induction, comparing rice (Oryza sativaL.) and barley (Hordeum vulgareL.) grains. While gibberellic acid (GA3) induces α‐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 α‐amylase. The level of ABA in anoxic tissues was found to be much lower than the threshold for α‐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 α‐amylase downstream of the slendermutation, 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 α‐amylase induction.

The aim of this study was to investigate the sugar-sensing processes modulating the expression of alpha-amylase in barley (Hordeum vulgaris L. var Himalaya) embryos. The results highlight the existence of independent glucose (Glc) and disaccharides sensing. Glc treatment destabilizes the alpha-amylase mRNA. Non-metabolizable disaccharides repress alpha-amylase induction, but have no effects on transcript stability. Structure-function analysis indicates that a fructose (Fru) moiety is needed for disaccharide sensing. Lactulose (beta-galactose [Gal][1-->4]Fru), palatinose (Glc[1-->6]Fru), and turanose (Glc[1-->3]Fru) are not metabolized but repress alpha-amylase. Disrupting the fructosyl moiety of lactulose and palatinose, or replacing the Fru moiety of beta-Gal[1-->4]Fru with Glc or Gal results in molecules unable to repress alpha-amylase. Comparison of the molecular requirements for sucrose transport with those for disaccharide sensing suggests that these sugars are perceived possibly at the plasma membrane level independently from sucrose transport.