Plant Growth Regulators
Auxins, gibberellins, cytokinins, ethylene and abscisic acid with physiological effects. (Biology › Plant Growth and Development, NEET UG syllabus.)
What is Plant Growth Regulators?
Small, simple organic molecules produced naturally in plants that regulate physiological processes like growth, development, and responses to the environment.
Key points
- Identify the five major classes of Plant Growth Regulators (PGRs).
- Describe the primary physiological effects of each class of PGRs.
- Explain the agricultural/horticultural applications of various PGRs.
- Differentiate between growth-promoting and growth-inhibiting PGRs.
Common exam trap
Confusing the roles of auxins (promote) and cytokinins (overcome) in apical dominance.
Definitions
- Term
Plant Growth Regulators (PGRs)
- Meaning
Small, simple organic molecules produced naturally in plants that regulate physiological processes like growth, development, and responses to the environment.
- Term
Auxins
- Meaning
A class of PGRs primarily involved in cell elongation, apical dominance, and root initiation. E.g., Indole-3-acetic acid (IAA).
- Term
Gibberellins
- Meaning
A class of PGRs known for promoting stem elongation (bolting), seed germination, and parthenocarpy. E.g., GA3.
- Term
Cytokinins
- Meaning
A class of PGRs that primarily promote cell division, delay senescence, and overcome apical dominance. E.g., Kinetin, Zeatin.
- Term
Ethylene
- Meaning
A gaseous PGR involved in fruit ripening, senescence, and abscission.
- Term
Abscisic Acid (ABA)
- Meaning
A PGR that acts as a general growth inhibitor, promoting dormancy, stomatal closure, and stress responses; often called the 'stress hormone'.
- Term
Apical Dominance
- Meaning
The phenomenon where the apical bud inhibits the growth of lateral (axillary) buds, primarily mediated by auxins.
- Term
Bolting
- Meaning
The rapid elongation of internodes in rosette plants just prior to flowering, induced by gibberellins.
- Term
Parthenocarpy
- Meaning
The development of fruit without fertilization, often induced by auxins or gibberellins, resulting in seedless fruits.
Learning objectives
Identify the five major classes of Plant Growth Regulators (PGRs).
Describe the primary physiological effects of each class of PGRs.
Explain the agricultural/horticultural applications of various PGRs.
Differentiate between growth-promoting and growth-inhibiting PGRs.
Understand the concept of synergism and antagonism among different PGRs.
Prerequisites
Basic understanding of plant anatomy (roots, stems, leaves, meristems).
Knowledge of fundamental plant physiological processes (e.g., photosynthesis, respiration, transpiration).
Familiarity with cell division (mitosis) and cell elongation.
Common mistakes
Confusing the roles of auxins (promote) and cytokinins (overcome) in apical dominance.
Attributing fruit ripening solely to all PGRs instead of primarily ethylene.
Forgetting that ethylene, while an inhibitor of growth in some contexts, also promotes root growth and root hair formation.
Not understanding the antagonistic relationship between ABA and Gibberellins in seed dormancy and germination.
Keywords
Phytohormones
Auxin
Gibberellin
Cytokinin
Ethylene
Abscisic Acid
Apical dominance
Bolting
Parthenocarpy
Senescence
Abscission
Dormancy
Stress hormone
IAA
GA3
Kinetin
Zeatin
Ethephon
2,4-D
Practice preview
Which plant growth regulator is often referred to as the 'stress hormone' due to its role in inducing dormancy and closing stomata under adverse conditions?…
easy
Which plant growth regulator is primarily responsible for apical dominance in plants?…
easy
The gaseous plant hormone known for promoting fruit ripening is:…
easy