What is seed germination?
The process of awakening of the embryo at the end of the dormancy period is called seed germination. The embryo lies dormant within the seed for a considerable period and germinates to give rise to seedling, which grows further and develop to produce an adult plant. Seed germination is the process of seeds developing into new plants. First, environmental conditions must trigger the seed to grow. Usually, this is determined by how deep the seed is planted, water availability, and temperature.
Condition for seed germination
There are both external and internal factors which are necessary for the germination of seeds. Those are as follows:
External factors of seed germination
There are four external factor for the seed germination; those are:
i) Air (or oxygen) supply: - Constant oxygen supply is necessary for increasing the respiratory rate of germinating seeds.
ii) Water or moisture : - Water is essential for bringing about the changes in the vital activities of a germinating seed, which comprise hydrolysis of the stored organic substances in the cotyledons. So, Water is crucial to seed germination. The seed must go through imbibitions to activate root growth.
iii) Light: - The process of seed germination can even occur in the darkness, so light has no direct effect on the seed germination, but it is quite necessary for the growth and development of the seedling.
iv) Temperature: - The optimum temperature is required to carry out certain fundamental activities in the protoplasm of the germinating seeds. Some seeds germinate when it is cold, such as plants in northern environments. Other seeds only germinate when the weather reaches spring temperatures, which is why we see so much plant growth in the spring like temperate climates. Other seeds only germinate after extreme temperatures.
Internal factors of seed germination
Three main internal factors for the germination of the seeds are as follow:
i) Dormancy period :- Each individual seed has a definite period of dormancy and seed germination takes place only after the dormancy period is over.
ii) Food : - The stored food is converted to simple soluble forms at the onset of seed germination by specific enzymes.
iii) Hormones : - The gibberellin hormone is responsible for the conversion of insoluble stored food into soluble forms. On the other hand, Auxin hormone is responsible for the growth and development of the seedling.
Important Events of Seed Germination
The various events that take place in a process of seed germination, those are as follows:
a) The hydrophilic colloid present in the seed coat absorbs water.
b) The seed swells up due to imbibitions of water by the inner tissue.
c) The seed coat ruptures under the pressure of the swelling seed.
d) The cell wall and protoplasm of the inner cells are hydrated.
e) The hormone gibberellin is activated.
f) De-novo synthesis of the enzyme a amylase takes place, which converts storage starch into soluble sugar.
g) Increase in osmotic potential causes greater absorption of water.
h) The soluble sugar is assimilated by the growing embryo.
i) The emergence of radical takes place and thus the seed germination is take place.