title: Metabolic and enzymatic changes associated with carbon mobilization, utilization and replenishment triggered in grain amaranth (Amaranthus cruentus) in response to partial defoliation by mechanical injury or insect herbivory.
abstract: BACKGROUND
  Amaranthus cruentus and A. hypochondriacus are crop plants grown for grain production in subtropical countries. Recently, the generation of large-scale transcriptomic data opened the possibility to study representative genes of primary metabolism to gain a better understanding of the biochemical mechanisms underlying tolerance to defoliation in these species. A multi-level approach was followed involving gene expression analysis, enzyme activity and metabolite measurements.
  
  
  RESULTS
  Defoliation by insect herbivory (HD) or mechanical damage (MD) led to a rapid and transient reduction of non-structural carbohydrates (NSC) in all tissues examined. This correlated with a short-term induction of foliar sucrolytic activity, differential gene expression of a vacuolar invertase and its inhibitor, and induction of a sucrose transporter gene. Leaf starch in defoliated plants correlated negatively with amylolytic activity and expression of a β-amylase-1 gene and positively with a soluble starch synthase gene. Fatty-acid accumulation in roots coincided with a high expression of a phosphoenolpyruvate/phosphate transporter gene. In all tissues there was a long-term replenishment of most metabolite pools, which allowed damaged plants to maintain unaltered growth and grain yield. Promoter analysis of ADP-glucose pyrophosphorylase and vacuolar invertase genes indicated the presence of cis-regulatory elements that supported their responsiveness to defoliation. HD and MD had differential effects on transcripts, enzyme activities and metabolites. However, the correlation between transcript abundance and enzymatic activities was very limited. A better correlation was found between enzymes, metabolite levels and growth and reproductive parameters.
  
  
  CONCLUSIONS
  It is concluded that a rapid reduction of NSC reserves in leaves, stems and roots followed by their long-term recovery underlies tolerance to defoliation in grain amaranth. This requires the coordinate action of genes/enzymes that are differentially affected by the way leaf damage is performed. Defoliation tolerance in grain is a complex process that can't be fully explained at the transcriptomic level only.
authors.affiliation: Unidad de Biotecnología e Ingeniería Genética de Plantas (Cinvestav-Irapuato), Km 9,6 del Libramiento Norte Carretera Irapuato-León, Apartado Postal 629, C,P, 36821, Irapuato, Gto, México.
authors.forename: Paula Andrea
authors.initials: PA
authors.lastname: Castrillón-Arbeláez
authors.forename: Norma
authors.initials: N
authors.lastname: Martínez-Gallardo
authors.forename: Hamlet Avilés
authors.initials: HA
authors.lastname: Arnaut
authors.forename: Axel
authors.initials: A
authors.lastname: Tiessen
authors.forename: John Paul
authors.initials: JP
authors.lastname: Délano-Frier
mesh_terms: D027721:Amaranthus / Q000201:enzymology* / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D050260:Carbohydrate Metabolism / Q000235:genetics; D002244:Carbon / Q000378:metabolism*; D003001:Cloning, Molecular; D003517:Cyclopentanes / Q000378:metabolism; D005632:Fructose / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics; D005947:Glucose / Q000378:metabolism; D005964:Glucosyltransferases / Q000235:genetics / Q000378:metabolism; D060434:Herbivory / Q000502:physiology*; D007313:Insecta / Q000502:physiology*; D008969:Molecular Sequence Data; D054883:Oxylipins / Q000378:metabolism; D018515:Plant Leaves / Q000502:physiology*; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D018547:Plant Stems / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012639:Seeds / Q000201:enzymology* / Q000235:genetics; D013213:Starch / Q000378:metabolism; D013314:Stress, Mechanical; D013395:Sucrose / Q000378:metabolism; D043324:beta-Fructofuranosidase / Q000235:genetics / Q000378:metabolism
chemical_list: D003517:Cyclopentanes; D054883:Oxylipins; D010940:Plant Proteins; D012333:RNA, Messenger; D005632:Fructose; D013395:Sucrose; C011006:jasmonic acid; D002244:Carbon; D013213:Starch; D005964:Glucosyltransferases; C022699:sucrose synthase; D043324:beta-Fructofuranosidase; D005947:Glucose