Plant Growth and Development
Key Concepts
- Growth: An irreversible increase in size and mass due to cell division and enlargement.
- Development: The process of becoming more complex and specialized.
- Totipotency: The ability of a plant cell to regenerate into a whole plant.
- Hormones: Chemical substances that regulate plant growth and development.
Phases of Plant Growth
1. Meristematic phase:
- Cells undergo rapid division, forming new cells.
- Found in meristems (apical, intercalary, and lateral).
2. Elongation phase:
- Cells increase in length due to water uptake.
- Occurs in regions behind the meristems.
3. Maturation phase:
- Cells differentiate into specialized tissues (e.g., xylem, phloem).
- Cell walls thicken and organelles develop.
Plant Hormones
Auxins:
- Promote cell elongation, root growth, and apical dominance.
- Involved in phototropism (bending towards light) and geotropism (bending towards gravity).
Gibberellins:
- Promote stem elongation, seed germination, and fruit development.
- Used commercially to increase fruit size.
Cytokinins:
- Promote cell division, delay senescence (aging), and stimulate shoot formation.
- Often used in tissue culture to regenerate plants.
Abscisic acid (ABA):
- Promotes seed dormancy, stomatal closure, and stress responses.
- Helps plants adapt to adverse conditions.
Ethylene:
- Promotes fruit ripening, leaf abscission, and senescence.
- Used commercially to ripen fruits artificially.
Plant Movements
1. Tropisms: Growth responses to environmental stimuli.
- Phototropism: Bending towards light.
- Geotropism: Bending towards gravity.
- Thigmotropism: Bending in response to touch.
2. Nastic movements: Non-directional movements triggered by environmental changes.
- Nyctinasty: Sleep movements (e.g., closing of leaves at night).
- Seismonasty: Movements in response to touch or shaking.
Plant Growth Regulators (PGRs)
- Synthetic compounds that mimic the effects of plant hormones.
- Used in agriculture to control weed growth, promote rooting, and improve crop yield.
FAQs on Plant Growth and Development
What is the difference between growth and development in plants?
Growth refers to an increase in size and mass due to cell division and enlargement, while development involves becoming more complex and specialized.
What are the three phases of plant growth?
Meristematic phase, elongation phase, and maturation phase.
What is totipotency in plants?
The ability of a plant cell to regenerate into a whole plant.
What is the role of auxins in plant growth?
Auxins promote cell elongation, root growth, and apical dominance.
What is the function of gibberellins in plants?
Gibberellins promote stem elongation, seed germination, and fruit development.
How do cytokinins affect plant growth?
Cytokinins promote cell division, delay senescence, and stimulate shoot formation.
What is the role of abscisic acid (ABA) in plants?
ABA promotes seed dormancy, stomatal closure, and stress responses.
What is the function of ethylene in plants?
Ethylene promotes fruit ripening, leaf abscission, and senescence.
What are tropisms in plants?
Tropisms are growth responses to environmental stimuli, such as phototropism (bending towards light) and geotropism (bending towards gravity).
What are nastic movements in plants?
Nastic movements are non-directional movements triggered by environmental changes, such as nyctinasty (sleep movements) and seismonasty (movements in response to touch or shaking).
What are PGRs?
PGRs are synthetic compounds that mimic the effects of plant hormones.
How are PGRs used in agriculture?
PGRs are used to control weed growth, promote rooting, and improve crop yield.
