title: Rice alcohol dehydrogenase 1 promotes survival and has a major impact on carbohydrate metabolism in the embryo and endosperm when seeds are germinated in partially oxygenated water.
abstract: OBJECTIVE
  Rice (Oryza sativa) has the rare ability to germinate and elongate a coleoptile under oxygen-deficient conditions, which include both hypoxia and anoxia. It has previously been shown that ALCOHOL DEHYDROGENASE 1 (ADH1) is required for cell division and cell elongation in the coleoptile of submerged rice seedlings by means of studies using a rice ADH1-deficient mutant, reduced adh activity (rad). The aim of this study was to understand how low ADH1 in rice affects carbohydrate metabolism in the embryo and endosperm, and lactate and alanine synthesis in the embryo during germination and subsequent coleoptile growth in submerged seedlings.
  
  
  METHODS
  Wild-type and rad mutant rice seeds were germinated and grown under complete submergence. At 1, 3, 5 and 7 d after imbibition, the embryo and endosperm were separated and several of their metabolites were measured and compared.
  
  
  RESULTS
  In the rad embryo, the rate of ethanol fermentation was halved, while lactate and alanine concentrations were 2·4- and 5·7- fold higher in the mutant than in the wild type. Glucose and fructose concentrations in the embryos increased with time in the wild type, but not in the rad mutant. The rad mutant endosperm had lower amounts of the α-amylases RAMY1A and RAMY3D, resulting in less starch degradation and lower glucose concentrations.
  
  
  CONCLUSIONS
  These results suggest that ADH1 is essential for sugar metabolism via glycolysis to ethanol fermentation in both the embryo and endosperm. In the endosperm, energy is presumably needed for synthesis of the amylases and for sucrose synthesis in the endosperm, as well as for sugar transport to the embryo.
authors.affiliation: Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8601, Japan.
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Takahashi
authors.forename: Hank
authors.initials: H
authors.lastname: Greenway
authors.forename: Hideo
authors.initials: H
authors.lastname: Matsumura
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Tsutsumi
authors.forename: Mikio
authors.initials: M
authors.lastname: Nakazono
mesh_terms: D000409:Alanine / Q000378:metabolism; D000426:Alcohol Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D050260:Carbohydrate Metabolism / Q000235:genetics; D018548:Cotyledon / Q000254:growth & development / Q000378:metabolism*; D056625:Endosperm / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D019344:Lactic Acid / Q000378:metabolism; D012275:Oryza / Q000196:embryology* / Q000201:enzymology* / Q000235:genetics / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012639:Seeds / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D013395:Sucrose / Q000378:metabolism; D000516:alpha-Amylases / Q000378:metabolism
chemical_list: D019344:Lactic Acid; D013395:Sucrose; D000426:Alcohol Dehydrogenase; D000516:alpha-Amylases; D000409:Alanine
keywords: ADH1; Oryza sativa; alcohol dehydrogenase; carbohydrate metabolism; embryo; endosperm; germination; reduced ADH activity; rice; submergence tolerance