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Process of Seed Germination

Requirements for Germination

Water: 

The role of wwater in germination is of paramount importance.The  seed  reemains in a ormant condirtion and the initiation of the process og germination takes place by the influx of water molecules.The seed has a tiny pore  in the covering (testa which is called micropyle and water enters into the seed initially by imbibation  adsorption ofwater by substances present inside the seed.Thses incluse proteins, starchand cell wall materials suach as hemicellulose and pectic substances.
The swelling of  tese substances ca lesd tot he strong imbiational forces which are great enough to cause rupturing of the seed.

                             Stages of Seed germination                            Stages of Seed germination  

Optimum  temperature  :

 There is a characteristic temperature range needed for proper germination of seeds  in a given soil type. It is about  5 to 400   C.  

Oxygen :

 This is required for aerobic respiration  which can be assisted with anaerobic respiration if needed

Plant growth is well explained with an example of germination of Bambarra Bean seed below.

germination of seed showing growth of a normal seed

Germination of Voandzeia (Bambarra Bean)

Plant growth is well explained with an example of germination of Bambarra Bean seed below.

germination of seed showing growth of a normal seed

Physiology of Germination:

  • A typical seed stores carbohydrates, lipids and proteins  for germination.
  • As a result of imbibation  and osmosis the embryo bercomes  hydrated which activates the enzymes for respiration.
  • basically the storage centre (food) and the growth centre(embryo) are the main regioons of activity.
  • Digestion of food on storage centre osccurs  by hydrolysis  and amino acids, sugars anf fatty acids anf glygerol arte produced
  • Soluble products are translocaterd to thegrowing regions of the embryo
  • The majority of glucose is used for cellulose synthesis and other cell wall materials.amino acids are used for enzymes and structural components.
  • The net loss of mass of the seed occurs due to  change of  sugars to  Co2  and water where C02 is lost as gas than Otaken up by aerobic respiration.
  • Within the embryo growth  occurs by cell division and amounts of proteins, cellulose,nucleic acids steadily increase in the growing regions of the seed.
  • Thev first visible sign of growth is the radicle, that emerges fromthe micropyle andis positively  geotropic in nature.It forms the rooyt system of the plant 
  • The next structure that emerges is the plumule, that is positively phototropic  and forms the shoot system of the plant.                           

 Stages of Seed Germination

There are basically three steps of seed germination:

  • Step 1-Water imbibation results in rupture of seed coat, uniform imbibation is important   and approximately optimum temperatures are required
  • Step 2-The imbibition of the seed coat results in emergence of the radicle and the plumule, the cotyledons get   unfolded. It is important that  the temperature and photo period  are required in optimum amounts
  • Step 3-This marks the final step in the germination of the seed  where the  cotyledons are expanded which are the true leaves.

 

For the growth and development of seeds ,different kinds of food like carbohydrates, fat and proteins are required in stored form.Besides the growth promoting substances  like auxins, heteroauxins  are also formed at the time of germination which controls the growth and development of seedlings during germination.

Germination of Voandzeia (Bambarra Bean)

Seed germination is an irreversible process. Germination includes the changes that take place from the time the dry seed is provided with suitable conditions to when the seedling becomes established as an independent plant. Various changes take place during germination.

They are as follows:

Sub Topics
 

Imbibition

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The first step in the process of seed germination is imbibition or absorption of water. The seed takes in water through the micropyle which results in swelling of the seed. This is due to the cellular constituents being dehydrated. The swelling causes the seed coat to rupture and enables the radicle to come out in the form of a primary root.

Respiration

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When the seed imbibes water, it causes the metabolic activities to resume. In the beginning the respiration is anaerobic and later it becomes aerobic.

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