title: The role of alpha-glucosidase in germinating barley grains.
abstract: The importance of α-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 α-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, α-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 α-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.
authors.affiliation: John Innes Centre, Norwich Research Park, Norwich NR4 7UH, United Kingdom.
authors.forename: Duncan
authors.initials: D
authors.lastname: Stanley
authors.forename: Martin
authors.initials: M
authors.lastname: Rejzek
authors.forename: Henrik
authors.initials: H
authors.lastname: Naested
authors.forename: Mark
authors.initials: M
authors.lastname: Smedley
authors.forename: Sofía
authors.initials: S
authors.lastname: Otero
authors.forename: Brendan
authors.initials: B
authors.lastname: Fahy
authors.forename: Frazer
authors.initials: F
authors.lastname: Thorpe
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Nash
authors.forename: Wendy
authors.initials: W
authors.lastname: Harwood
authors.forename: Birte
authors.initials: B
authors.lastname: Svensson
authors.forename: Kay
authors.initials: K
authors.lastname: Denyer
authors.forename: Robert A
authors.initials: RA
authors.lastname: Field
authors.forename: Alison M
authors.initials: AM
authors.lastname: Smith
mesh_terms: D050260:Carbohydrate Metabolism; D018525:Germination; D005947:Glucose / Q000378:metabolism; D001467:Hordeum / Q000201:enzymology* / Q000235:genetics; D008320:Maltose / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics; D034622:RNA Interference; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D036226:Seedlings / Q000378:metabolism; D012639:Seeds / Q000201:enzymology*; D013213:Starch / Q000378:metabolism; D000520:alpha-Glucosidases / Q000235:genetics / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D011994:Recombinant Proteins; D008320:Maltose; D013213:Starch; D000520:alpha-Glucosidases; D005947:Glucose