Plant Growth Regulators: Overview, Types, Its Role In Plant Growth
Plant Growth Regulators (PGRs) are hormone-like chemical messengers that control every stage of plant development—from seed germination and stem elongation to fruit ripening and stress responses. They include natural phytohormones like auxins, cytokinins, gibberellins, ABA, and ethylene. Understanding PGRs is essential for NEET and agriculture because they regulate plant physiology and are widely used in crop improvement.
This Story also Contains
- What Are Plant Growth Regulators?
- Classification of Plant Growth Regulators
- Discovery Of Plant Growth Regulators
- Types of Plant Growth Regulators and Their Functions
- Mechanism of Action of PGRs
- Applications Of Plant Growth Regulators
- Differences Between Growth Promoters & Growth Inhibitors
- Plant Growth Regulators NEET MCQs (With Answers & Explanations)
- Recommended Video On 'Plant Growth Regulators'
What Are Plant Growth Regulators?
Plant growth regulators are either natural or artificial substances that can manipulate all phases of plant growth and development, including cell division, cell elongation, and cell differentiation. They have a crucial role in controlling physiological activities such as flowering, fruiting, and responses to stress, and are important tools in agriculture and horticulture in optimising plant health and productivity.
Classification of Plant Growth Regulators
The plant growth regulators are classified into two main categories, i.e., growth promoters and growth inhibitors
Growth Promoters
Growth promoters enhance the growth of the plant. Below are the types of plant growth regulators:
Auxins are a class of phytohormones mainly influencing plant growth through cell elongation and cell differentiation.
Gibberellins are hormones that affect the growth and development of plants, including stem elongation and seed germination.
Cytokinins are hormones that enhance cell division and shoot development; they have an antiaging effect in plants.
Growth Inhibitors
Growth inhibitors slow or stop the growth of the plant. Below are the types of plant growth inhibitors:
Abscisic acid is a plant hormone that mediates responses to plant stress and dormancy in seeds.
Ethylene is a gaseous phytohormone that tends to affect several growth events of plants, primarily fruit ripening and the abscission of leaves.
Discovery Of Plant Growth Regulators
Early Observations: Details regarding plant hormones and their role in growth were finalised by the end of the 19th and beginning of the 20th centuries.
Auxins: Its existence was shown by Charles Darwin and his son Francis, who showed its role in phototropism.
Gibberellins: It was isolated from the fungus Gibberella fujikuroi which caused abnormal growth in rice.
Cytokinins: It was isolated from coconut milk since it allows cell division.
Abscisic Acid: It was isolated for its role in the abscission of leaves and other organs and its response to different stresses.
Types of Plant Growth Regulators and Their Functions
The different types of plant growth regulators and their functions are:
Auxin
Function And Mechanism
Cell Elongation: It causes elongation through the loosening of cell walls.
Root Development: Required for root initiation and growth
Tropisms: Channels growth responses of plants to environmental stimuli, such as light, and gravity.
Key Examples
Indole-3-acetic Acid, IAA: The most ubiquitous naturally occurring auxin that is implicated in many growth events.
Gibberellins
Function And Mechanism
Stem Elongation: The cell will start to elongate and divide into stems.
Seed Germination: Break dormancy of seed and lead to germination
Flowering: affects flowering in some plants
Key Examples
Gibberellic acid, GA: The most famous Gibberellin used in promoting growth and production yield.
Cytokinins
Function And Mechanism
Cell Division: Induce mitosis in plant cells.
Shoot Development: Promote shoot growth and leaf expansion.
Delay Senescence: Extend the life of leaves and other plant organs.
Key Examples
Zeatin: Produced in maize and induces cell division.
Kinetin: An artificial cytokinin used to study tissue culture and plant growth.
ABA
Function And Mechanism
Stress Response: It helps the plants fight drought and other stress conditions.
Seed Dormancy: It causes dormancy and prevents the seed from germinating prematurely.
Key Examples
ABA in Drought Tolerance: It enhances the water-retention ability of the plant and decreases the rate of transpiration.
Ethylene
Function and Mechanism
Fruit Ripening: It speeds up fruit ripening.
Leaf Abscission: It causes the fall of leaves and flowers.
Commercial Fruit Ripening: Used to synchronize and control the ripening process of fruits like bananas and tomatoes.
Mechanism of Action of PGRs
The signal transduction pathways of different PGRs:
Plant Growth Regulators | Mechanism |
Auxins | Acting on receptors, changes gene expression and causes cell elongation. |
Gibberellins | Activating transcription factors that stimulate growth. |
Cytokinins | Inducing signalling cascades that promote cell division. |
Abscisic Acid | Turning on stress response genes and closing stomata. |
Ethylene | Modify enzyme activities that control fruit ripening and senescence. |
Applications Of Plant Growth Regulators
The applications of PGRs are explained below:
Agriculture
Used to enhance crop yield and productivity.
Growth enhancement: Size and quality of crops enhanced.
Disease resistance: Plants are more resistant to diseases.
Examples Of PGRs Used In Agriculture
Gibberellins: Used on plants to increase fruit size and seed size.
Cytokinin: Used on crops to promote yield and quality.
Ornamental Plants
Flowering: The extent and time of flowering can be induced.
Aesthetics: Modify the shape of plants and the appearance of foliage.
Environmental Management
PGRs are involved in maintaining and restoring the environment.
Promotion of Growth: This accelerates the growth of reforested areas.
Stress Tolerance: This promotes the survival of plants on degraded soils.
Differences Between Growth Promoters & Growth Inhibitors
The difference between growth promoters and growth inhibitors is:
Feature | Growth Promoters | Growth Inhibitors |
Examples | Auxins, GAs, Cytokinins | ABA, Ethylene |
Effect | Stimulate growth | Suppress growth |
Process | Cell elongation, division | Dormancy, ab scission |
Seed germination | Promote | Inhibit |
Plant Growth Regulators NEET MCQs (With Answers & Explanations)
Important topics for NEET are:
Types of Plant Growth Regulators
Mechanism of Action
Practice Questions for NEET
Q1. Name the plant growth regulator, which, upon spraying on sugarcane crops, increases the length of the stem, thus increasing the yield of sugarcane crops.
Cytokinin
Gibberellin
Ethylene
Abscisic acid
Correct answer: 2) Gibberellin
Explanation:
The plant growth hormone gibberellin helps in the elongation of stems in crops such as sugarcane.
When applied to sugarcane plants, it promotes the development of taller stems, resulting in increased yields.
This hormone is frequently utilized in agriculture since it is essential for encouraging cell elongation.
Farmers can increase crop yield and have better outcomes with crops that need vertical growth by utilizing gibberellins.
Hence, the correct answer is option 2) Gibberellin.
Q2. The cells in watermelon may increase in size by up to 3,50,000 times. This phenomenon is called
Hypotrophy
Hypertrophy
Hyperplasia
Hypoplasia
Correct answer: 2) Hypertrophy
Explanation:
Hypertrophy is the increase in the size of cells leading to the enlargement of a tissue or organ. HypertrophyHypertrophy typically occurs as a response to increased demand or stress. For instance, muscle hypertrophy takes place when muscle fibres grow larger due to exercise, especially through strength training. While physiological hypertrophy is generally healthy, pathological hypertrophy, such as that occurring in the heart due to high blood pressure, can impair function and lead to complications.
Hence, the correct answer is option 2) Hypertrophy.
Q3. Growth promoting hormone is
Auxin
Gibberellin
Cytokinin
All of the above
Correct answer: 4) All of the above
Explanation:
The PGRs can be broadly divided into two groups based on their functions in a living plant body:
Growth promoting such as mediating cell division, cell enlargement, pattern formation, tropic growth, flowering, fruiting, and seed formation.
Growth inhibiting such as mediating responses to wounds and stresses of biotic and abiotic origin.
Auxin, gibberellin, and cytokinins are growth-promoting hormones.
Hence the correct answer is option 4) All of the above.
Also Read:
Recommended Video On 'Plant Growth Regulators'
Frequently Asked Questions (FAQs)
Auxins cause an increase in cell length and initiate root growth. They also participate in tropisms, allowing plants to grow and set their direction correctly in response to the environment.
Gibberellins break dormancy and activate the events needed for the germination of seeds, which in turn favours more homogeneous and successful sprouting.
Cytokinins increase cell division, improve crop yields by allowing an increased number of reproductive structures to be present on a plant, and delay leaf senescence—all factors important for the enhancement of crop productivity and quality.
If not controlled, synthetic PGRs would mean overexploitation, environmental hazards, and probably human health risks, so that their application and safety measures should be strictly controlled.
Plant Growth Regulators, PGRs are substances that alter or modify plants' growth and development. They are crucial in maximising agricultural production, enhancing yields, and creating a balance within the plants.
