Notes on plant growth and development

 **Plant Growth and Development:**

1. **Plant Growth:**

   - Growth is irreversible increase in size or mass.

   - Meristems, regions of actively dividing cells, contribute to plant growth.

2. **Plant Tissues:**

   - Meristematic Tissues: Actively dividing cells in regions like apical and lateral meristems.

   - Permanent Tissues: Mature, specialized cells in various plant organs.

3. **Primary and Secondary Growth:**

   - Primary Growth: Lengthening of stems and roots due to apical meristems.

   - Secondary Growth: Increase in girth or thickness, facilitated by lateral meristems (vascular cambium and cork cambium).

4. **Plant Hormones:**

   - Auxins: Promote cell elongation and are involved in apical dominance.

   - Gibberellins: Stimulate stem elongation and seed germination.

   - Cytokinins: Promote cell division and influence shoot development.

   - Ethylene: Controls fruit ripening and leaf abscission.

   - Abscisic Acid (ABA): Inhibits growth, regulates seed dormancy, and stress responses.

5. **Photoperiodism:**

   - Response of plants to the duration of light and darkness.

   - Influences flowering and other developmental processes.

6. **Vernalization:**

   - Exposure of certain plants to a period of cold to induce flowering.

   - Prevents premature flowering in some species.

7. **Senescence:**

   - Aging process in plants leading to cell and tissue death.

   - Triggered by factors like hormones, environmental cues, and nutrient availability.

8. **Tropisms:**

   - Plant responses to external stimuli.

   - Examples: phototropism (response to light), gravitropism (response to gravity).

9. **Apical Dominance:**

   - Suppression of lateral bud development by the apical bud.

   - Influences the shape and structure of the plant.

10. **Seed Germination:**

    - Activation of a dormant seed to grow into a seedling.

    - Involves water uptake, enzymatic activation, and growth of the embryo.

11. **Role of Mycorrhizae:**

    - Symbiotic associations between plant roots and fungi.

    - Enhance nutrient absorption, especially phosphorus.

12. **Plant Reproduction:**

    - Asexual reproduction: Cloning through methods like runners or cuttings.

    - Sexual reproduction: Formation of seeds through fertilization.

Understanding plant growth and development is crucial for agriculture, horticulture, and ecological restoration efforts. It involves the coordination of genetic, hormonal, and environmental factors influencing various stages of a plant's life cycle.