Hormones

• Growth

  Permanent increase in size of an organ or its part or an individual cell
• Plant growth

  • Plants show unlimited growth throughout their life
  • Due to the presence of meristems at certain locations in their body
• Root apical meristem and shoot apical meristem


  • Responsible for the primary growth of plants
  • Contribute to the elongation of the plants along their axis
• Dicotyledons and gymnosperms

  • Have lateral meristems, i.e. vascular cambium and cork cambium
  • Contribute to the increase in the girth of the stem
• Growth

  • Consequence of increase in the amount of protoplasm of the cell
  • Can be measured by increase in fresh weight, dry weight, length, area, volume and cell number
• Growth period

  1. Meristematic

  2. Elongation

  3. Maturation
• Growth rate

  • Increase in growth per unit time
  • Can be arithmetic or geometrical
• Phases of growth

  • Lag
  • Log
  • Senescent
• Conditions for growth

  • Optimum availability of water, oxygen and nutrients
• Environmental conditions affecting growth

  • Temperature
  • Light
  • Gravity
• Differentiation

  Cells derived from meristems differentiate and mature to perform specific functions
• Dedifferentiation


  Differentiated cells regain the capacity of division
• Redifferentiation

  Dedifferentiated cells again lose the capacity and mature to perform specific functions
• Plant development

  • Flexible and open
  • Sum of growth and differentiation
  • Plants exhibit plasticity in response to environment
• Plant growth regulators (PGRs)

  • Auxins
  • Gibberellins
  • Cytokinins
  • Abscisic acid
  • Ethylene
• PGRs

  • Control different developmental events
  • Divided into growth promoters and growth inhibitors
• Ethylene


  Gaseous plant growth regulator
• ABA


  Stress hormone
• PGRs can act antagonistically or synergistically
• Environmental factors affecting plant growth and development

  • Light
  • Temperature
  • Nutrition
  • Oxygen status
  • Gravity
• Cytokinins are growth promoters
• Ethylene is a simple gaseous plant promoter
• Auxins are plant growth hormone
• Auxin promotes apical dominance
• Auxin promotes initiation of roots
• Auxin promotes cell elongation
• Auxin promotes flowering
• Auxins promotes parthenocarpy
• Auxins promote metabolism
• Gibberellins promote elongation of internodes
• gibberellins promotes elongation of genetically dwarf plants
• Gibberellins promote bolting
• Gibberellins helps in breaking seed dormancy
• Gibberellins help in flowering
• Cytokinins helps in the growth of the shoot and root systems of a plant
• Cytokinins helps in promoting cell division
• Cytokinins helps in morphogenesis
• Cytokinins reduces apical dominance
• Cytokinins helps in resistance
• Cytokinins delays senescence