Glucose and disaccharide-sensing mechanisms modulate the expression of alpha-amylase in barley embryos

The aim of this study was to investigate the sugar-sensing processes modula ting the expression of alpha-amylase in barley (Hordeum vulgaris L. var Him alaya) embryos. The results highlight the existence of independent glucose (Glc) and disaccharides sensing. Glc treatment destabilizes the alpha-amyla se mRNA. Non-metabolizable disaccharides repress alpha-amylase induction, b ut have no effects on transcript stability. Structure-function analysis ind icates that a fructose (Fru) moiety is needed for disaccharide sensing. Lac tulose (beta-galactose [Gal][1-->4]Fru), palatinose (Glc[1-->6]Fru), and tu ranose (Glc[1-->3]Fru) are not metabolized but repress or-amylase. Disrupti ng the fructosyl moiety of lactulose and palatinose, or replacing the Fru m oiety 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 a re perceived possibly at the plasma membrane level independently from sucro se transport.