Plant Hormones (Phytohormones)

What are Plant Hormones?

Plant hormones, also known as phytohormones, are chemical messengers that regulate various functions in plants like growth, flowering, fruiting, seed germination, leaf fall, and stress response. They are produced in very small amounts and can act locally or be transported to other parts of the plant.

Types of Plant Hormones

• 1. Auxins: Promote cell elongation, root initiation, and are responsible for phototropism and geotropism.
• 2. Gibberellins: Stimulate stem elongation, seed germination, and flowering.
• 3. Cytokinins: Promote cell division and delay aging in leaves (senescence).
• 4. Abscisic Acid (ABA): Inhibits growth, causes stomatal closure during water stress, and promotes dormancy.
• 5. Ethylene: A gaseous hormone that promotes fruit ripening and leaf abscission.

Functions of Plant Hormones

• Regulate plant growth and development
• Control processes like flowering, fruiting, seed germination
• Help in stress tolerance (drought, salinity, etc.)
• Coordinate responses to environmental stimuli

Examples of Practical Uses

• Auxins: Used in rooting powders to promote root growth in cuttings.
• Ethylene: Used to ripen fruits like bananas and mangoes artificially.
• ABA: Helps plants survive drought conditions.

Previous Year Questions

• HSSC JE 2021: Which plant hormone is responsible for fruit ripening?
  • Option A: Auxin
  • Option B: Cytokinin
  • Option C: Ethylene
  • Option D: Gibberellin

  Correct Answer: C. Ethylene

• RRB JE 2019: Which hormone promotes cell division in plants?
  • Option A: Gibberellin
  • Option B: Cytokinin
  • Option C: Abscisic acid
  • Option D: Ethylene

  Correct Answer: B. Cytokinin

• SSC JE 2020: Which of the following plant hormones causes the closing of stomata during water stress?
  • Option A: Auxin
  • Option B: Cytokinin
  • Option C: Abscisic Acid
  • Option D: Gibberellin

  Correct Answer: C. Abscisic Acid