Germination is a succession of steps that resume the embryo's development and the beginning of the formation of a new seedling.
We can summarize germination as the process of transforming the seed into a new plant.
The seed is made up of the embryo, endosperm and integument. During germination, the embryo is nourished by the endosperm.
germination
Factors Affecting Germination
For germination to occur, certain conditions that depend on environmental factors and the seed itself are necessary.
The main factors affecting germination are:
- water availability
- Oxygen
- Light
- Temperature
- Seed Wrap Permeability
- Chemical substances
- seed numbness
Among all the factors, water is the most determinant for germination. Imbibition, the process of capturing water, hydrates the tissues and intensifies the metabolic activities necessary for the resumption of growth in the embryonic axis.
Despite the importance of water, its excess causes a decrease in germination, as it prevents oxygen penetration.
Naturally, seeds germinate as soon as they find favorable environmental conditions. However, other seeds need to overcome the dormant state before germination.
The germination and breaking of seed dormancy also depend on the action of the plant hormones, like the gibberellins.
Germination Phases
Germination can be divided into three phases: imbibition, growth induction and embryonic axis growth.
Imbibition Phase
The imbibition phase consists of the capture of water that causes the initial wetting of the tissues closest to the surface.
The amount of water absorbed must be sufficient not only to start germination, but also to ensure that the process goes through to completion.
Growth Induction Phase
At this stage there is a reduction in water uptake. New tissue is formed and metabolism is activated.
Embryonic Axis Growth Phase
The growth phase comprises the cell expansion process and the disruption of the integument with the protrusion of the radicle (embryonic root). The radicle is the first part to emerge from the seed.
Types of Germination
Germination can be of two types: epigeal and hypogeal.
Epigean germination: cotyledons rise above the ground. It's typical of dicots.
Hypogeal germination: the cotyledons remain in the ground. It's typical of monocots.
Cotyledons are the embryonic leaves of plants, formed by the seed and important for the initial development of plants. They are the first leaves that emerge from the embryo.
The number of cotyledons in the seed classifies plants into monocotyledons and dicots.