Germination in Plants: The Birth of a New Plant

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Germination


Germination

Germination is the process by which the embryo grows and develops, eventually becoming a fully mature plant. It is the onset growth of a seed, often following a period of dormancy or the emergence of embryo from the seed coat due to onset of growth and development of the seed.  The pattern of germination is similar in most dicotyledonous seeds.


Mechanism of Seed Germination

During seed germination, seed absorbs water through the micropyle. The tissues absorb water and swell and the testa becomes soft. The radicle grows first, pushing though the testa and entering the soil. Next, either the hypocotyl or the epicotyl, depending on the species, starts to elongate and carry the plumule upwards through the soil.  

Dormancy is the resting period in which growth stops temporarily and metabolism is reduced to its barest minimum. Dormant seed may survive adverse conditions such as drought, flood low and high temperature.


Stages of Germination

Germination involves several key stages:

  1. Imbibition: The seed absorbs water, causing it to swell and break the seed coat. This initial step activates metabolic processes necessary for growth.

  2. Activation of Metabolism: Enzymes and hormones are activated, breaking down stored food reserves in the endosperm or cotyledons. This provides energy and nutrients for the growing embryo.

  3. Radicle Emergence: The embryonic root (radicle) emerges first, anchoring the seedling into the soil and beginning the process of water and nutrient uptake.

  4. Shoot Emergence: The embryonic shoot (plumule) emerges, pushing upwards towards the light. This stage includes the development of the first true leaves.

  5. Seedling Establishment: The seedling develops its root and shoot systems, establishing itself as an independent plant capable of photosynthesis and further growth.


Conditions or Requirements for Germination 

A viable seed can only germinate if the following environmental factors are available:

  1. Water: seeds need a supply of water. This softens the testa or fruit wall and allows the radicle to grow and push its way out. Water activates the enzymes which convert the starch stored in the cotyledons or endosperm into soluble sugars which are then transported in solution to the growing regions.

  2. Oxygen: Required for cellular respiration, which provides energy for the growing embryo.

  3. Temperature: Optimal temperature ranges vary by species, but most seeds require moderate warmth to activate enzymes and support growth.

  4. Light: Some seeds require light to germinate (photoblastic seeds), while others do not. Light can influence the direction and growth rate of the emerging shoot.

  5. Nutrients: While the seed contains initial food reserves, soil nutrients become important once the seedling begins to establish itself.


Types of Germination

1.  Epigeal – type of germination where the cotyledon appears above the ground.  It causes by elongation of the hypocotyl of the radicle.   E.g., groundnut, cowpea, castor oil.

2.  Hypogeal – type of germination where the cotyledon remains below the ground. It is cause by elongation of the epicotyl of the plumule during germination, e.g., guinea corn, maize

Whichever pattern of germination occurs, the energy and raw materials required for growth come from the food (usually starch) stored in the cotyledon.


Differences between epigeal and hypogeal germination  

Epigeal germination

Hypogeal germination

Testa split

Pericarp split

Hypocotyl emerges uncovered

Hypocotyl covered by the sheath/coleorhiza 

Cotyledons are carried above the soil

Cotyledons remain in the soil

Hypocotyl elongates

Epicotyl elongate/straightens out

Cotyledon is the first photosynthetic tissue until true foliage leaves develops

Cotyledons wither so true foliage leaves are first photosynthetic tissue

Energy obtained from food stored in the cotyledon

Energy obtained from food stored in the endosperm

 

types of germination



Hypogeal germination of seed


Significance of Germination

  1. Plant Propagation: Germination is the first step in plant propagation, allowing plants to reproduce and spread.

  2. Agricultural Productivity: Successful germination is crucial for crop production. Understanding germination can help improve agricultural practices and yields.

  3. Ecological Balance: Germination contributes to the maintenance of plant populations and biodiversity in ecosystems.

  4. Seedling Establishment: Germination ensures that the new plant can establish itself and grow independently, starting the life cycle anew.


Conclusion

Germination is a complex and vital process that marks the beginning of a seed's transformation into a new plant. Understanding the stages, requirements, types, and significance of germination provides valuable insights into plant biology and ecology. This knowledge is essential for agriculture, horticulture, and conservation efforts, ensuring successful plant propagation and growth.

For further reading, visit Germination on Britannica and Importance of Germination on National Geographic.



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