Explain the process of germination in seeds with the help of diagram. Also describe the importance of air, water and warmth in the process.
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Explain the process of germination in seeds with the help of diagram. Also describe the importance of air, water and warmth in the process.
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Such five changes or steps occurring during seed germination are: (1) Imbibition (2) Respiration (3) Effect of Light on Seed Germination(4) Mobilization of Reserves during Seed Germination and Role of Growth Regulators and (5) Development of Embryo Axis into Seedling.
(i) Imbibition:
The first step in the seed germination is imbibition i.e. absorption of water by the dry seed. Imbibition results in swelling of the seed as the cellular constituents get rehydrated. The swelling takes place with a great force. It ruptures the seed coats and enables the radicle to come out in the form of primary root.
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Imbibition is accomplished due to the rehydration of structural and storage macromolecules, chiefly the cell wall and storage polysaccharides and proteins. Many seeds contain additional polysaccharides, not commonly found in vegetative tissues. Seeds packed dry in a bottle can crack it as they imbibe water and become swollen.
(ii) Respiration:
Imbibition of water causes the resumption of metabolic activity in the rehydrated seed. Initially their respiration may be anaerobic (due to the energy provided by glycolysis) but it soon becomes aerobic as oxygen begins entering the seed. The seeds of water plants, as also rice, can germinate under water by utilizing dissolved oxygen.
The seeds of plants adapted to life on land cannot germinate under water as they require more oxygen. Such seeds obtain the oxygen from the air contained in the soil. It is for this reason that most seeds are sown in the loose soil near the surface. Ploughing and hoeing aerate the soil and facilitate seed germination. Thus the seeds planted deeper in the soil in water-logged soils often fail to germinate due to insufficient oxygen.
(iii) Effect of Light on Seed Germination:
Plants vary greatly in response to light with respect to seed germination. The seeds which respond to light for their germination are named as photoblastic. Three categories of photoblastic seeds are recognized: Positive photoblastic, negative photoblastic and non-photoblastic. Positive photoblastic seeds (lettuce, tobacco, mistletoe, etc.) do not\u00a0