Model Answer
0 min readIntroduction
Phytohormones, also known as plant hormones, are naturally occurring organic compounds that regulate plant growth and development. They are crucial for various processes, from seed germination to senescence. Recent advancements in plant biotechnology have focused on manipulating phytohormone levels to enhance crop yields and resilience. Unlike animal hormones, phytohormones are often synthesized in multiple tissues and have pleiotropic effects, meaning a single hormone can influence several physiological processes. This answer will detail the physiological roles of two key phytohormones: auxins and gibberellins.
What are Phytohormones?
Phytohormones are signaling molecules that influence various aspects of plant life. They are produced in small quantities and act locally or are transported to other parts of the plant to elicit a response. They interact with each other, exhibiting synergistic or antagonistic effects. Key phytohormones include auxins, gibberellins, cytokinins, abscisic acid, ethylene, brassinosteroids, jasmonates, and salicylic acid.
Auxins: The Growth Promoters
Auxins, primarily Indole-3-acetic acid (IAA), are pivotal in cell elongation, apical dominance, and root initiation. They were the first plant hormones to be discovered, initially by Frits Went’s experiments with oat coleoptiles.
- Cell Elongation: Auxins stimulate the production of cell wall loosening enzymes, leading to cell expansion.
- Apical Dominance: They inhibit the growth of lateral buds, ensuring the main stem's dominance.
- Root Initiation: Auxins promote the formation of adventitious roots, crucial for vegetative propagation.
- Phototropism & Gravitropism: Auxin redistribution causes bending towards light (phototropism) and gravity (gravitropism).
Example: The use of auxins like NAA (Naphthalene Acetic Acid) in horticulture for root induction in plant cuttings is a common practice.
Gibberellins: The Stem Elongators
Gibberellins (GAs) are a family of hormones that primarily promote stem elongation, seed germination, and flowering. Over 130 gibberellins have been identified, with GA3 being the most extensively studied.
- Stem Elongation: GAs stimulate cell division and elongation, resulting in taller plants.
- Seed Germination: They overcome seed dormancy and promote germination by mobilizing stored nutrients.
- Flowering: In some plants, GAs induce flowering, particularly in long-day plants.
- Fruit Development: GAs can increase fruit size and parthenocarpy (seedless fruit development).
Example: Grapes treated with gibberellins exhibit larger berry size and improved yield. Dwarf varieties of plants (e.g., dwarf pea) are often deficient in gibberellins.
| Feature | Auxins | Gibberellins |
|---|---|---|
| Primary Function | Cell elongation, apical dominance | Stem elongation, seed germination |
| Key Hormone | IAA (Indole-3-acetic acid) | GA3 |
| Effect on Roots | Promotes root initiation | Can stimulate root growth at lower concentrations |
Conclusion
In conclusion, phytohormones are essential regulators of plant growth and development, influencing a wide range of physiological processes. Auxins primarily govern cell elongation and apical dominance, while gibberellins are crucial for stem elongation and seed germination. Understanding the intricate interplay of these hormones is vital for improving crop production and developing strategies for sustainable agriculture. Further research into phytohormone signaling pathways holds immense potential for enhancing plant resilience in the face of climate change.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.