Introduction
Brief introduction of seed germination
Seed germination, which determines when the plant enters natural or agricultural ecosystems, is a crucial process in the seed plant life cycle and the basis for crop production. The germination of freshly produced seeds is inhibited by primary dormancy, which helps the seeds equip for environments with unfavorable conditions . The seeds will enter a germinating state from the dormant state at an appropriate time when the dormancy is lost through moist chilling (stratification) or after-ripening. Therefore, seed germination is a accurately timed checkpoint to avoid unsuitable weather and unfavorable environments during plant establishment and reproductive growth.
Task
Step 1: Soak the seeds a day before conducting the experiment. This plays an important role in bringing about faster results.
Step 2: Drain the water from the seeds before placing them in the bag. Damp a paper towel and fold it into a bag, seal it tightly and hang the bag in a window.
Step 3: Approximately after 24 hours, you will be able to observe the seeds opening up and sprouting. Within 2-3 days, these seeds will be fully sprouted and after a few more days, small leaves start to develop.
Process
The process of germination can be understood in five different stages mentioned below:
Imbibition: It is the process of absorption of water by dry seeds. Imbibition leads to swelling of the seeds. Absorption of water leads to rupturing of the seed coat.
Respiration: Imbibition of water stimulates metabolic activity in the seed. Initially, seeds undergo anaerobic respiration as energy is provided by glycolysis; as oxygen starts entering the seed, they perform aerobic respiration.
Plants that grow on land acquire oxygen from the air present in the soil. This is the reason we plough and loosen the soil before sowing them. Seeds of water plants use oxygen dissolved in the water.
Effect of Light on Seed Germination: Plants are classified as photoelastic and non-photoelastic based on their response to light for germination. Non-photoelastic plants germinate irrespective of the presence or absence of light.
Positive photoelastic seeds require exposure to light and cannot germinate in the absence of it, whereas negatively photoelastic seeds can germinate only in the dark.
Mobilisation of Reserved Food During Seed Germination: The cotyledons of seed store food for the embryo. During germination, starch, fats and proteins stored in the endosperm are digested to produce the energy required for metabolic activities and multiple cell divisions in the embryo by aerobic respiration.
Enzymes such as amylases, proteases, etc., are released during this to promote the breakdown of complex food material into a form that can be used by the embryo. Water helps in the translocation of these soluble food materials to growing parts of the seed, mainly radicle and plumule.
Development of Embryo Axis into Seedling: After the translocation of food materials embryo multiplies rapidly, resulting in the rapid growth of the seed into a seedling. The radicle of the seed grows first to form the root that grows down into the soil and begins to absorb water and minerals from the soil. After this, the plumule grows in an upwards direction to form the shoot.
When the shoot grows above the ground, it develops green leaves. Green leaves of shoots begin to synthesise their food in the presence of sunlight (photosynthesis).
Evaluation
Count out 100 seeds from each sample and place on absorbent material inside the tray. For each of 10 days, check to see that the absorbent material remains moist and record the number of germinated seeds. Compute germination test after five days, and another after ten days.
Conclusion
Seeds have the ability to germinate in the presence of moisture, air, and light under the right temperature, even in the absence of soil. If you are interested in knowing more about seed germination, you can repeat the same experiment but keep the bag in a dark place instead of placing it in light.