Seed germination is the process by which a dormant seed resumes growth and develops into a seedling under favorable conditions. It involves a series of biochemical and physiological changes leading to the emergence of the embryonic root (radicle) and shoot (plumule).
Process of Germination:
1. Imbibition: The seed absorbs water, which activates enzymes and softens the seed coat.
2. Enzyme Activation: The absorbed water triggers enzymes that convert stored food (starch) into energy.
3. Cell Division and Growth: The cells in the embryo divide rapidly, and the seed coat breaks open.
4. Emergence of Radicle and Plumule: The radicle emerges first to form roots, followed by the plumule, which grows into the shoot.
Types of Germination:
1. Epigeal Germination:
The cotyledons (seed leaves) are pushed above the soil due to the elongation of the hypocotyl.
Example: Beans, Castor.
2. Hypogeal Germination:
The cotyledons remain underground, and the plumule emerges above the soil as the epicotyl elongates.
Example: Pea, Maize.
Conditions Required for Germination:
1. Water: Essential for activating enzymes and softening the seed coat.
2. Oxygen: Required for respiration, which provides energy for growth.
3. Temperature: Suitable temperatures (15-30°C) enhance enzymatic activity.
4. Light/Darkness: Some seeds require light (lettuce) or darkness (onion) for germination.