title: Auxin increases the hydrogen peroxide (H2O2) concentration in tomato (Solanum lycopersicum) root tips while inhibiting root growth.
abstract: OBJECTIVE
  The hormone auxin and reactive oxygen species (ROS) regulate root elongation, but the interactions between the two pathways are not well understood. The aim of this study was to investigate how auxin interacts with ROS in regulating root elongation in tomato, Solanum lycopersicum.
  
  
  METHODS
  Wild-type and auxin-resistant mutant, diageotropica (dgt), of tomato (S. lycopersicum 'Ailsa Craig') were characterized in terms of root apical meristem and elongation zone histology, expression of the cell-cycle marker gene Sl-CycB1;1, accumulation of ROS, response to auxin and hydrogen peroxide (H2O2), and expression of ROS-related mRNAs.
  
  
  RESULTS
  The dgt mutant exhibited histological defects in the root apical meristem and elongation zone and displayed a constitutively increased level of hydrogen peroxide (H2O2) in the root tip, part of which was detected in the apoplast. Treatments of wild-type with auxin increased the H2O2 concentration in the root tip in a dose-dependent manner. Auxin and H2O2 elicited similar inhibition of cell elongation while bringing forth differential responses in terms of meristem length and number of cells in the elongation zone. Auxin treatments affected the expression of mRNAs of ROS-scavenging enzymes and less significantly mRNAs related to antioxidant level. The dgt mutation resulted in resistance to both auxin and H2O2 and affected profoundly the expression of mRNAs related to antioxidant level.
  
  
  CONCLUSIONS
  The results indicate that auxin regulates the level of H2O2 in the root tip, so increasing the auxin level triggers accumulation of H2O2 leading to inhibition of root cell elongation and root growth. The dgt mutation affects this pathway by reducing the auxin responsiveness of tissues and by disrupting the H2O2 homeostasis in the root tip.
authors: Department of Botany and Plant Pathology, Oregon State University, 2082 Cordley Hall, Corvallis, OR 97331, USA.
authors: Maria G
authors: MG
authors: Ivanchenko
authors: Désirée
authors: D
authors: den Os
authors: Gabriele B
authors: GB
authors: Monshausen
authors: Joseph G
authors: JG
authors: Dubrovsky
authors: Andrea
authors: A
authors: Bednárová
authors: Natraj
authors: N
authors: Krishnan
mesh_terms: D018506:Gene Expression Regulation, Plant / Q000187:drug effects*; D005819:Genetic Markers; D006706:Homeostasis; D006861:Hydrogen Peroxide / Q000378:metabolism*; D018546:Hypocotyl / Q000166:cytology / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D007210:Indoleacetic Acids / Q000378:metabolism / Q000494:pharmacology*; D018551:Solanum lycopersicum / Q000166:cytology / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D018519:Meristem / Q000166:cytology / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D009154:Mutation; D010937:Plant Growth Regulators / Q000378:metabolism / Q000494:pharmacology*; D018517:Plant Roots / Q000166:cytology / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics; D018749:RNA, Plant / Q000235:genetics; D017382:Reactive Oxygen Species / Q000378:metabolism*
chemical_list: D005819:Genetic Markers; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D012333:RNA, Messenger; D018749:RNA, Plant; D017382:Reactive Oxygen Species; D006861:Hydrogen Peroxide
keywords: Auxin; ROS; Solanum lycopersicum; dgt; diageotropica; hydrogen peroxide; root elongation; tomato
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