Plant Growth and Development: Correct Statements on PGRs and Differentiation | NEET Biology
Read the following statements on plant growth and development:
  • (A) Parthenocarpy can be induced by auxins.
  • (B) Plant growth regulators can be involved in promotion as well as inhibition of growth.
  • (C) Dedifferentiation is a pre-requisite for re-differentiation.
  • (D) Abscisic acid is a plant growth promoter.
  • (E) Apical dominance promotes the growth of lateral buds.

Choose the option with all correct statements:

Correct Answer: (C) A, B, C only

Detailed Explanation

To find the correct option, let's analyze each statement based on NCERT biology:

  • Statement (A) is Correct: Auxins are known to induce parthenocarpy (fruit formation without fertilization) in plants like tomatoes.
  • Statement (B) is Correct: Plant Growth Regulators (PGRs) are divided into two groups: promoters (Auxins, Gibberellins, Cytokinins) and inhibitors (Abscisic acid, Ethylene).
  • Statement (C) is Correct: In plants, differentiated cells can regain the power of division (dedifferentiation) to form a meristem, which then produces cells that differentiate again (redifferentiation).
  • Statement (D) is Incorrect: Abscisic acid (ABA) is a growth inhibitor, not a promoter. It is involved in seed dormancy and closing of stomata.
  • Statement (E) is Incorrect: Apical dominance inhibits the growth of lateral buds. It is the removal of shoot tips (decapitation) that promotes lateral bud growth.

Since A, B, and C are correct, the most appropriate option is (C).

Related Theory: Plant Growth Regulators (PGRs)

PGRs are small, simple molecules of diverse chemical composition that control all phases of plant growth.

1. Growth Promoters vs. Inhibitors

  • Promoters: Perform growth-promoting activities like cell division, cell enlargement, pattern formation, and flowering. (Example: Auxins, Gibberellins, Cytokinins).
  • Inhibitors: Important for responses to wounds and stresses of biotic and abiotic origin. They induce dormancy and abscission. (Example: Abscisic Acid).
  • Ethylene: A gaseous PGR that fits into both categories but is largely an inhibitor of growth activities.

2. Differentiation, Dedifferentiation, and Redifferentiation

Plants have unique flexibility in their development:

  • Differentiation: Cells derived from root/shoot apical meristems mature to perform specific functions.
  • Dedifferentiation: Mature cells regain the capacity to divide under certain conditions (e.g., formation of interfascicular cambium).
  • Redifferentiation: Cells produced by dedifferentiated tissues lose their capacity to divide again and mature to perform specific tasks.

3. Apical Dominance

In most higher plants, the growing apical bud inhibits the growth of the lateral (axillary) buds. This phenomenon is caused by Auxins. Decapitation (removing the tip) allows lateral buds to grow, a practice used widely in tea plantations and hedge-making.

Frequently Asked Questions (FAQs)

1. Which PGR is known as the "Stress Hormone"? Abscisic Acid (ABA) is called the stress hormone because it increases the tolerance of plants to various kinds of stresses.
2. What is parthenocarpy? It is the development of fruit without fertilization, resulting in seedless fruits.
3. How does decapitation help in tea plantations? Removing shoot tips breaks apical dominance, allowing lateral buds to grow and making the plant bushier.
4. Give an example of dedifferentiation. The formation of interfascicular cambium and cork cambium from fully differentiated parenchyma cells.
5. Which PGR is gaseous in nature? Ethylene is the only gaseous plant growth regulator.
6. What is the role of Cytokinins? They help overcome apical dominance and promote nutrient mobilization.
7. Does ABA promote or inhibit seed germination? ABA inhibits seed germination and promotes seed dormancy.
8. What is 'plasticity' in plant growth? The ability of plants to follow different pathways in response to environment or phases of life to form different kinds of structures (e.g., heterophylly in cotton).
9. Which hormone is used to kill dicotyledonous weeds? 2,4-D (an Auxin) is widely used as a herbicide to kill dicot weeds.
10. What is redifferentiation? It is the process where cells formed by dedifferentiated tissues lose their ability to divide and mature for specific functions.

Author: Jee neet experts

Plant Physiology Specialist with extensive experience in creating NCERT-based content for medical aspirants.

Related Covered Topics

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