Plant Hormones Quiz: Auxins and Cytokinins

Auxins and Cytokinins

• Main auxins: indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), 1-naphthaleneacetic acid (NAA), 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), Picloram, Dicamba, and p-chlorophenoxyacetic acid (CPA)
• Main cytokinins: zeatin (Z), zeatinriboside (ZR), isopentenyladenine (iP), 6-benzylaminopurine (BAP), 6-furfurylaminopurine (kinetin), and thidiazuron (TDZ)

Plant Hormone Action in Plant Tissue Culture

• Callus tissue is generated from leaf explants of Arabidopsis halleri and Arabidopsis thaliana
• Friable callus is produced and transferred to shoot regeneration media, followed by root regeneration media
• The final step is the removal of the fully regenerated plants to the greenhouse
• Friable callus can also be used to generate stable cell suspension cultures

Plant Hormones (Growth Regulators)

• Hormones are "chemical messengers" influencing plant development
• Plant hormone: a natural substance produced by plants that acts to control plant activities
• Classical plant hormones: Auxin, Gibberellins, Cytokinins, Abscisic Acid, and Ethylene
• New generation plant hormones: Brassinosteroids, Salicylic acid, Jasmonic acid, Peptides, and Polyamines

Auxin and Cytokinin Function

• Auxin is produced in the apex and upper part of the stem and transported downwards
• Auxin and cytokinin penetrate the axillary bud and inhibit and promote outgrowth, respectively
• Cytokinin is produced in the roots and transported upwards in the stem
• Strigolactone (SL) reduces auxin transport capacity, inhibiting axillary bud outgrowth

Effects of Hormones in Tissue Culture

• Auxin:
  • Formation of meristems of adventitious roots
  • Induction of somatic embryos
  • Cell division and callus formation
  • Inhibition of outgrowth of axillary buds
• Cytokinin:
  • Stimulation of outgrowth of axillary buds
  • Inhibition of shoot elongation
  • Inhibition of leaf senescence
  • Promotion of cell division and callus formation
• Gibberellin:
  • Release from dormancy in seeds, somatic embryos, apical buds, and bulbs
  • Inhibition of adventitious root formation
  • Synthesis-inhibitors promote root formation
• Ethylene:
  • Ripening of fruits
  • Promotion or inhibition of adventitious regeneration
  • Maturation of somatic embryos
  • Facilitation of acclimatization
• Abscisic acid:
  • Inhibition of root growth
  • Promotion of the development of dormancy

Modulators of Hormone Metabolism, Action, or Transport

• 2,3,4-Triiodobenzoic acid (TIBA) and 1-N-naphthylphthalamic acid (NPA) inhibit polar auxin transport
• p-Chlorophenoxyisobutyric acid (PCIB) inhibits auxin action
• Phenolic compounds (e.g. ferulic acid or phloroglucinol) inhibit auxin oxidation
• Lovastatin inhibits cytokinin synthesis
• Paclobutrazole, ancymidol, and flurprimidol inhibit gibberellin synthesis
• 1-Aminocyclopropane-1-carboxylic acid (ACC) is a precursor of ethylene
• Aminoethoxyvinylglycine (AVG) inhibits ethylene synthesis

Test your knowledge on plant hormones by identifying main auxins and cytokinins such as indole-3-acetic acid, zeatin, and more. Learn about the functions and characteristics of these important plant growth regulators.