A Look Inside Seed Germination
- erudite .
- Dec 4, 2021
- 3 min read
By Ella Kang
Almost all the plants that we have seen or eaten so far grow from a single seed. The process in which a plant develops its essential parts like roots, stems, and leaves from its seed is referred to as seed germination! Below is a diagram depicting a series of sequential events in seed germination.
Step 1: Imbibition
The seed absorbs water from the surroundings. The water is about half its weight. This thus causes the seed coat to become soft and swell.
Step 2: Activation
The absorbed water activates the enzymes inside the seed, causing the embryo to enter the development phase. The seed begins to breathe by absorbing oxygen and using the food it has stored to create the proteins needed to develop.
Step 3: Growth
This is the part where root and shoot form. The seed coat ruptures when the rate of respiration rises, forming a radical that subsequently grows into the main root, while the plumule develops into a shoot. Enzymatic activity continues at an all-time peak at this time.
Step 4: Morphogenesis
When the first embryonic leaf, or cotyledon, emerges, this is the last stage of seed germination. Foliage leaves are small leaves that emerge from the terminals of the shoots throughout time. The young plant continues to eat the nourishment contained in the seed throughout this stage of growth and eventually starts to produce its own through photosynthesis.
But most importantly, the seed requires a favourable environment in order to trigger the stages of germination.
Water
The availability of water is critical for the seed’s enzymatic activity and metabolism to begin. Water intake inside the seed also causes the seed coat to break, allowing the seedling to emerge from the seed.
Temperature
Each seed has a certain temperature range for germination, but in general, the higher the temperature, the faster the germination rate. Most seeds germinate at temperatures ranging from 16 to 24°C.
Oxygen
In the presence of oxygen, the respiratory rate of germinating seeds rises. Because respiration is a metabolically active seed's primary source of energy, oxygen becomes a critical element in germination. A seed that lacks oxygen will stay inactive or dormant, unable to enter the metabolically active stage.
Light
The presence or lack of light is one of the most critical variables for a seed to germinate. Positive photoelastic seeds are those that respond to light for germination, and negatively photoelastic seeds are those that germinate exclusively in darkness.
Soil salinity
High salt concentrations in the soil prevent the seed from absorbing water, rendering the soil unsuitable for germination. The seed will go dormant as a result of this. Soil salinity can be reduced by frequent watering and the application of organic fertilizers.
Seed viability
The presence of the growth hormone gibberellin aids seed germination and the development of a young plant by allowing the seed coat to shed. Immature embryos do not germinate until they reach full development. Depending on the plant type, a seed can be viable for germination for a week to several years.
Moreover, germination processes differ in monocots and dicots.
Germination in monocots (oats, corn, bamboo)
The main root develops from the seed and grows downwards during the germination of monocots. The main leaf of the plant then emerges and develops upwards while a cylindrical, hollow structure known as the coleoptile, protects it. And when the seedling reaches the top of the earth, the coleoptile stops growing and is penetrated by the main leaf.
Germination in dicots (bean, tomato, sunflower)
When dicot seeds are immersed in soil, the main root develops through the seed coat during germination. The seed coat sprouts a dicotyledonous stem (hypocotyl) that shoots upwards through the soil. Hypocotyl arch is the form it adopts as it grows up, like a hairpin. The plumule is an epicotyl structure that is shielded from harm by two cotyledons. When the hypocotyl arch emerges from the earth, it continues to develop straight, with the direction of growth controlled by light.
In an adequate environment, a seed usually germinates within 1 to 2 weeks. Some seeds, however, might take up to 3 weeks to germinate.
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