L3 | PHYTOHORMONES

• PHYTOHORMONES

  • Plant hormone
  • Chemical messengers that regulate plant growth, development, and reproduction.
• HORMONES

  • Chemical substances that act like messenger molecules
• MAJOR TYPES OF PHYTOHORMONES

  1. GROWTH INDUCER HORMONE
  2. AUXIN
  3. GIBBERELLINS
  4. CYTOKININS
  5. GROWTH INHIBITOR HORMONE
  6. ABSCISIC ACID
  7. ETHYLENE (ETHENE)
• AUXIN

  • Growth inducer hormone
  • Cell elongation
  • Lengthening of a cell during cell differentiation process
  • Found in growing regions of the plant
  • Important for phototropism
• TROPISM

  • Directional growth of an organism in response to a stimulus
• 2 TYPES OF TROPISM

  1. POSITIVE TROPISM
  2. NEGATIVE TROPISM
• POSITIVE TROPISM

  • Action is towards the stimulus
• NEGATIVE TROPISM

  • Action is away from the stimulus
• EXAMPLES OF TROPISM

  1. PHOTOTROPISM
  2. GEOTROPISM
  3. HYDROTROPISM
  4. THIGMOTROPISM
• GEOTROPISM

  • Growth of plants in response to the force of gravity
• HYDROTROPISM

  • Plant’s growth response in which the direction is determined by a gradient in water concentration
• THIGMOTROPISM

  • Directional response of a plant organ to touch or make a physical contact with a solid object.
• GIBBERELLIN

  • Growth inducer hormone
  • Stem elongation, germination, and flowering
  • Promotes: cell enlargement & cell differentiation in the presence of auxins
  • Induce parthenocarpy
  • Formation of seedless fruits without fertilization
• CYTOKININS

  • Growth inducer hormone
  • Cell division
  • Cyto – “cell”; Kinin – “division”
  • Occur in greater concentration in areas of rapid cell division such as fruits and seeds.
  • Delay the aging in leaves
  • Promote the opening of stomata
• ABSCISIC ACID

  • Growth inhibitor 
  • “Abscission”
  • Falling of leaves
  • Closing of stomata thus affects wilting of leaves.
• ETHYLENE (ETHENE)

  • Growth inhibitor 
  • Ripening of fruits
  • Stimulates the formation of separation layer abscission zone in leaves, flowers, and fruits.
  • Promotes yellowing of leaves 
• GROWTH TO MATURITY

  1. Gibberellin
  2. Auxin
  3. Cytokinins
• FLOWERING

  1. Gibberellin
  2. Auxin
  3. Cytokinin
  4. Ethylene
• GERMINATION

  1. Gibberellin
• FRUIT DEVELOPMENT

  1. Gibberellin
  2. Auxin
  3. Cytokinins
  4. Ethylene
• ABSCISSION

  1. Ethylene
  2. Abscisic Acid
• SEED DORMANCY

  1. Abscisic acid