title: Gibberellin is required for the formation of tension wood and stem gravitropism in Acacia mangium seedlings.
abstract: OBJECTIVE
  Angiosperm trees generally form tension wood on the upper sides of leaning stems. The formation of tension wood is an important response to gravitational stimulus. Gibberellin appears to be involved in the differentiation of secondary xylem, but it remains unclear whether gibberellin plays a key role in the formation of tension wood and plant gravitropism. Therefore, a study was designed to investigate the effects of gibberellin and of inhibitors of the synthesis of gibberellin, namely paclobutrazole and uniconazole-P, on the formation of tension wood and negative stem gravitropism in Acacia mangium seedlings.
  
  
  METHODS
  Gibberellic acid (GA(3)), paclobutrazole and uniconazole-P were applied to seedlings via the soil in which they were growing. Distilled water was applied similarly as a control. Three days after such treatment, seedlings were tilted at an angle of 45° from the vertical, and samples of stems were collected for analysis 2 weeks, 2 months and 6 months after tilting. The effects of treatments on the stem recovery degree (Rº) were analysed as an index of the negative gravitropism of seedlings, together the width of the region of tension wood in the upper part of inclined stems.
  
  
  RESULTS
  It was found that GA(3) stimulated the negative gravitropism of tilted seedling stems of A. mangium, while paclobutrazole and uniconazole-P inhibited recovery to vertical growth. Moreover, GA(3) stimulated the formation of tension wood in tilted A. mangium seedlings, while paclobutrazole and uniconazole-P strongly suppressed the formation of tension wood, as assessed 2 weeks after tilting.
  
  
  CONCLUSIONS
  The results suggest that gibberellin plays an important role at the initial stages of formation of tension wood and in stem gravitropism in A. mangium seedlings in response to a gravitational stimulus.
authors: Tokyo University of Agriculture and Technology, Fuchu-Tokyo, Japan.
authors: Widyanto Dwi
authors: WD
authors: Nugroho
authors: Yusuke
authors: Y
authors: Yamagishi
authors: Satoshi
authors: S
authors: Nakaba
authors: Shiori
authors: S
authors: Fukuhara
authors: Shahanara
authors: S
authors: Begum
authors: Sri Nugroho
authors: SN
authors: Marsoem
authors: Jae-Heung
authors: JH
authors: Ko
authors: Hyun-O
authors: HO
authors: Jin
authors: Ryo
authors: R
authors: Funada
mesh_terms: D000045:Acacia / Q000166:cytology / Q000187:drug effects* / Q000254:growth & development / Q000502:physiology; D005875:Gibberellins / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology*; D018522:Gravitropism / Q000187:drug effects* / Q000502:physiology; D010937:Plant Growth Regulators / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology*; D018547:Plant Stems / Q000166:cytology / Q000187:drug effects / Q000254:growth & development / Q000502:physiology; D036226:Seedlings / Q000166:cytology / Q000187:drug effects / Q000254:growth & development / Q000502:physiology; D012987:Soil; D014197:Trees; D014230:Triazoles / Q000494:pharmacology; D014934:Wood
chemical_list: D005875:Gibberellins; D010937:Plant Growth Regulators; D012987:Soil; D014230:Triazoles; C511205:uniconazole-P; C053370:paclobutrazol; C007842:gibberellic acid