The Role of α-Glucosidase in Germinating Barley Grains    

Abstract

The importance of a-glucosidase in the endosperm starch metabolism of barley (Hordeum vulgare) seedlings is poorly understood. The enzyme converts maltose to glucose (Glc), but in vitro studies indicate that it can also attack starch granules. To discover its role in vivo, we took complementary chemical-genetic and reverse-genetic approaches. We identified iminosugar inhibitors of a recombinant form of an a-glucosidase previously discovered in barley endosperm (ALPHA-GLUCOSIDASE97 [HvAGL97]), and applied four of them to germinating grains. All four decreased the Glc-to-maltose ratio in the endosperm 10 d after imbibition, implying inhibition of maltase activity. Three of the four inhibitors also reduced starch degradation and seedling growth, but the fourth did not affect these parameters. Inhibition of starch degradation was apparently not due to inhibition of amylases. Inhibition of seedling growth was primarily a direct effect of the inhibitors on roots and coleoptiles rather than an indirect effect of the inhibition of endosperm metabolism. It may reflect inhibition of glycoprotein-processing glucosidases in these organs. In transgenic seedlings carrying an RNA interference silencing cassette for HvAgl97, a-glucosidase activity was reduced by up to 50%. There was a large decrease in the Glc-to-maltose ratio in these lines but no effect on starch degradation or seedling growth. Our results suggest that the a-glucosidase HvAGL97 is the major endosperm enzyme catalyzing the conversion of maltose to Glc but is not required for starch degradation. However, the effects of three glucosidase inhibitors on starch degradation in the endosperm indicate the existence of unidentified glucosidase(s) required for this process.

Transgenic barley lines prove the involvement of TaCBF14 and TaCBF15 in the cold acclimation process and in frost tolerance

“…CBF transcription factors belong to the CBF/DREB1 subfamily in the ERF family and AP2/ERF (APETALA2/ethylene-responsive factor) superfamily. As their name, CRT/DRE-binding factor (Stockinger et al ., 1997; Liu et al ., 1998), indicates, they can bind to the promoter of the above-mentioned target genes. CBF proteins are distinguished from the other members of the AP2/ERF protein family by the ‘CBF signature’ conserved amino acid sequence as well as by the PKK/RPAGRxKFxETRHP and DSAWR motifs present in the N- and C-terminal flanking region, respectively (Jaglo et al ., 2001).…”

Characterization of OsSUT2 Expression and Regulation in Germinating Embryos of Rice Seeds

“…Sugar derived from starch degradation exported to the cytosol from storage organelles is the first step for longdistance carbohydrate translocation. In cereal endosperms, starch granules are attacked by α-amylase (Murata et al 1968), and the maltose and linear/short-branch-chain oligosaccharides are generated for further degradation by α-glucosidase (Stanley et al 2011). The hexoses produced by starch degradation can be taken up by the scutellum cells of the embryo.…”

Microbial β-Glucosidases: Screening, Characterization, Cloning and Applications

“…Probably the most studied one is the lysosomal acid β-glucosidase (3.2.1.45) which hydrolyzes β-glucosyl linkage of glucosylceramide releasing ceramide and involved in Gaucher's disease pathogenesis [17]. In plants, β-glucosidases are involved in many physiological processes such as cell wall lignification [18], seed germination [19], phytohormones activation [20], indole alkaloids biosynthesis [21], cyanogenesis [22], and defense against biotic stresses by releasing of toxic…”