The hormone that primarily stimulates growth and promotes germination is Gibberellin.
Gibberellins (GAs) are a class of plant hormones that play crucial roles in various developmental processes, including stem elongation, seed germination, dormancy, flowering, sex expression, enzyme induction, and leaf and fruit senescence. Their effect on growth and germination makes them vital for plant life cycles.
How Gibberellins Promote Growth:
- Cell Elongation: Gibberellins promote cell elongation, leading to increased stem and shoot growth. They do this by increasing cell wall plasticity, allowing cells to expand.
- Cell Division: Gibberellins can also stimulate cell division in some plant tissues, contributing to overall growth.
- Stem Elongation in Rosette Plants: In rosette plants (like cabbages), gibberellins trigger bolting - the rapid elongation of the stem in preparation for flowering.
How Gibberellins Promote Germination:
- Breaking Seed Dormancy: Many seeds have a period of dormancy before they can germinate. Gibberellins can break this dormancy, signaling the seed to begin the germination process.
- Enzyme Production: Gibberellins stimulate the production of enzymes, such as amylase, which break down stored food reserves (e.g., starch) in the seed. This provides the energy and building blocks needed for the developing seedling.
- Mobilizing Nutrients: By activating hydrolytic enzymes, Gibberellins mobilize nutrients stored in the endosperm, making them available for the growing embryo.
Therefore, Gibberellins are critical for both stimulating growth and promoting germination in plants.
