Glucose and Disaccharide-Sensing Mechanisms Modulate the Expression of α-amylase in Barley Embryos

The aim of this study was to investigate the sugar-sensing processes modulating the expression of α-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 α-amylase mRNA. Non-metabolizable disaccharides repress α-amylase induction, but have no effects on transcript stability. Structure-function analysis indicates that a fructose (Fru) moiety is needed for disaccharide sensing. Lactulose (β-galactose [Gal][1→4]Fru), palatinose (Glc[1→6]Fru), and turanose (Glc[1→3]Fru) are not metabolized but repress α-amylase. Disrupting the fructosyl moiety of lactulose and palatinose, or replacing the Fru moiety of β-Gal[1→4]Fru with Glc or Gal results in molecules unable to repress α-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.