Definition of Seed Germination:
Seed germination is the process by which a plant grows from a seed. In another word; Seed germination is the process of active growth. The embryo is resulting in the rupture of the seed coat and emergence of the new young plant under the favorable condition of water, oxygen, temperature, and sometimes light.
Botanically, germination may be defined as the emergence and development of the seed embryo of those essential structures that for the kind of seeds in questions are indicated to produce a normal plant under favourable condition. It is expressed in terms of percentage.
Process of seed germination:
The germination process may be divided into the following stages-
- Imbibition of water
- Enzymatic and respiratory activities
- Digestion and translocation of food
Imbibition of water:
In a moist medium, the seed absorbs water with or without any intervallic lack period. The water absorption depends upon the kinds of seeds. In legumes, water enters the seed through the strophiole and others through Hilum tissue. Some species absorb water from all parts of the seed coat.
The water uptake is very rapid in cereal grain. The growing embryo is specially separated from storage endosperm then the metabolic activity is enhanced. The seed protein contains hydration of water and also absorb a sufficient amount of moisture. The swelling of the seed often causes the bursting of the seed coat in many species, like swelling of both water and gas and emerging of the growing point.
Enzymatic and respiratory activities:
This stage is characterized by the initiation of cellular activity with the appearance of specific enzymes and increases the respiratory rate. The storage tissue of endosperm and cotyledon of germinating seeds, hydrology whose activity promotes mobilization of the reserved compound in seed and activation of the respiratory enzyme.
In cereal, one of the detectable features of the metabolic activity is the activation of mRNA accomplished by an increase in the embryo’s capacity to synthesize protein. This follows the imbibition of water for only a few minutes. Polysome begins to increase with the respiration rate and extension of some cell within the first 12-16 hours, the synthesis of new DNA and RNA particularly nil.
By this time, there has been some extension growth of the existing cell. The early stages of meiotic cell division can be recognized. During the first 24 hours, the extension and division depend entirely on amino acid, fats, and soluble carbohydrate stored in the embryo.
During this period, a considerable amount of gibberellin is secreted by the embryo. The primary mode of action of gibberellin on stimulating RNA synthesis or the synthesis of α-amylase. It plays an essential role in nucleic acid metabolism and protein synthesis.
Digestion and translocation of food:
Digestion is the chemically breaking down of complex food to a simple one done by the hydrolytic enzyme. The starch, lipid and protein is digested by diastase (α-amylase) lipase and protease into sugar, fatty acid and amino acid. Digested foods such as Glucose, Fructose, maltose, Fatty acid, Amino acid are translocated to the active growing area.
Assimilation is the process by which the digested food becomes a part of the living protoplasm. The assimilation takes the place of the meristematic area to provide cellular activity growth of embryo and conservation into new cell component.
The seedling grows by cell division, enlargement and differentiation of cell at the growing point. The growth and development of seedling depend upon food reserved in the seed. The emergence of Plumule above the ground brings the plant under the influence of light and result in the suppression of mesocycle, hypocotyl or epicotyl growth and stimulating the formation of chlorophyll.
They are followed a transition period during which photosynthesis gradually assumes. Seedling of wheat becomes completely independent when the second leaf fully emerges and the third just emerging. Cucumber seedling becomes independent soon after the unfolding of the cotyledon.