The seeds are usually composed of embryo, endosperm and integument. They protect the embryo that will give rise to a new plant. The embryo remains in latency until it finds favorable environmental conditions to develop.
What is germination ? The beginning of a new plant’s growth process through the embryo contained in the seed or spore is called germination.
The seeds can remain dormant for long periods, thus being able to distribute germination over time.
Dormancy is an internal block that prevents the seed from germinating, and may be the stiff integument or a suppressed chemical.
The end of numbness allows metabolic activity to resume and germination to occur.
Factors affecting germination
For germination to happen, it is important that some factors are in favorable conditions. The main ones are:
- Water availability
- Temperature
- Oxygen
- Brightness
- Seed wrap permeability
- In some cases, chemical substances
- Breaking dormancy
- Plant hormones such as gibberellin
The availability of water is the determining factor for the beginning of germination since the intensification of metabolic activity is activated by the entry of water in the seed. However, excess water prevents germination as it prevents oxygen from entering cells.
The action of gibberellin can soften the integument cells, facilitating the entry of water and the subsequent exit of tissues from the embryo.
Germination stages
Imbibition
Water absorption phase to moisten the tissues closest to the seed surface. The amount of water captured must be sufficient for the entire germination process.
Growth induction
Here, there is a decrease in water absorption and the proliferation of meristematic cells occurs, thus initiating the formation of new tissues.
Embryonic axis growth
In this phase there is the rupture of the seed coat, the emergence of the radicle (root primordium), the allocation of substances from the endosperm and the cellular expansion that will originate the other tissues.
Cotyledon desiccation
After the appearance of the first true leaves, the cotyledons are reabsorbed by the new plant.
Types of germination
The types of germination are determined by the position of the cotyledons, embryonic leaves, during germination.
- Epigea: hypocotyl elongation occurs and, therefore, cotyledons rise above the ground, generally occurring in eudicotyledons . Example: beans.
Bean germination
- Hypogea : cotyledons remain below ground, it is the type of germination that normally occurs in monocots.
