Model Answer
0 min readIntroduction
Plant hormones, also known as phytohormones, are organic substances that influence physiological processes within plants. These chemical messengers regulate growth, development, and responses to environmental stimuli. Identifying these hormones often relies on observing their specific effects on plant tissues. Indole-3-acetic acid (IAA) is a primary auxin, Gibberellic acid (GA3) promotes stem elongation, and Kinetin is a cytokinin involved in cell division. Recognizing the unique physiological responses induced by each hormone is crucial for their identification and understanding their roles in plant life.
Indole-3-Acetic Acid (IAA) – Physiological Responses for Identification
IAA, the most common naturally occurring auxin, exhibits several characteristic physiological responses:
- Apical Dominance: IAA produced in the apical bud inhibits the growth of lateral buds. Removing the apical bud and applying IAA to the cut surface will restore apical dominance, demonstrating its role.
- Root Initiation: IAA promotes the formation of adventitious roots on stem cuttings. This is widely used in vegetative propagation. Concentration is critical; too much IAA can inhibit root formation.
- Tropic Responses: IAA mediates phototropism (growth towards light) and gravitropism (growth in response to gravity). Unequal distribution of IAA on the shaded side of a stem causes differential growth, bending the stem towards light.
- Cell Elongation: IAA stimulates cell elongation, particularly in stem tissues. This can be measured by observing increased stem length in treated plants.
- Ethylene Production: IAA can induce ethylene production, which contributes to fruit ripening and senescence.
Gibberellic Acid (GA3) – Physiological Responses for Identification
GA3 is known for its role in promoting stem elongation and seed germination. Key responses for identification include:
- Stem Elongation: GA3 dramatically increases stem length, especially in dwarf varieties. This is a classic test for GA3 activity. For example, in genetically dwarf pea plants, GA3 treatment restores normal height.
- Seed Germination: GA3 breaks seed dormancy and promotes germination, even in seeds that require stratification or light exposure. It stimulates the synthesis of hydrolytic enzymes like amylase, mobilizing stored food reserves.
- Bolting in Rosette Plants: GA3 induces bolting (rapid stem elongation) in rosette plants like lettuce and cabbage, preparing them for flowering.
- Flowering: GA3 can induce flowering in long-day plants under non-inductive conditions.
- Fruit Development: GA3 promotes fruit set and development, sometimes resulting in parthenocarpic fruits (fruit development without fertilization).
Kinetin – Physiological Responses for Identification
Kinetin, a cytokinin, primarily influences cell division and differentiation. Identifying responses include:
- Cell Division: Kinetin promotes cell division, particularly in callus cultures. When combined with auxin, it induces cell proliferation in tissue culture.
- Delay of Senescence: Kinetin delays leaf senescence (aging) by preventing chlorophyll degradation and protein breakdown. This is often observed as a prolonged green color in detached leaves treated with kinetin.
- Bud Formation: Kinetin promotes bud formation in tissue culture, especially when combined with auxin in appropriate ratios.
- Apical Dominance Modification: Kinetin can counteract apical dominance induced by IAA, promoting lateral bud growth.
- Nutrient Mobilization: Kinetin promotes the mobilization of nutrients to the sites of cell division and growth.
| Hormone | Key Physiological Response | Identification Method |
|---|---|---|
| IAA | Apical Dominance | Observe inhibition of lateral bud growth; restore dominance with IAA application. |
| GA3 | Stem Elongation | Measure stem length increase in dwarf varieties after GA3 treatment. |
| Kinetin | Delay of Senescence | Observe prolonged green color in detached leaves treated with kinetin. |
Conclusion
Identifying IAA, GA3, and Kinetin relies on observing their distinct physiological effects on plant growth and development. IAA governs apical dominance and root initiation, GA3 promotes stem elongation and seed germination, and Kinetin influences cell division and delays senescence. These responses, when carefully observed and quantified, provide reliable methods for hormone identification and contribute to a deeper understanding of plant hormonal regulation. Further research continues to unravel the complex interactions between these and other plant hormones.
Answer Length
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