The germination process – If the proper circumstances are met and the embryo is alive, the seed will begin to grow. This is referred to as germination. Here’s how it occurs: When you began the seed germination test in activity 1B, the radish seeds were hard and dry.
However, their appearance has now changed. The seeds have sprouted. The testa has been softened and divided by water. This helps the seed to absorb water and oxygen. A seed requires energy before it can germinate. The seed’s stored nutrients are converted into energy for the developing embryo. This is referred to as respiration.
Respiration requires oxygen, which is derived from the air. During respiration, this oxygen interacts with the food to release stored energy necessary for development. Water penetrates the seed through the micropyle, a microscopic pore in the testa. The water is subsequently utilised for chemical processes within the seed’s cells.
Warmth is required to accelerate the chemical processes occurring in the seed. Warmth also accelerates the production of new cells as the plant embryo grows. Consequently, low soil temperatures, for instance, will retard the pace of germination. Each plant species has a certain temperature range in which its seeds will germinate.
After water and oxygen reach the seed, the radicle is the first portion of the plant embryo to develop. Soon, it will emerge from the seed. The plumule then emerges. The green foliage grows and functions. They will now produce plant food through the process of photosynthesis.
During what time period is a plant embryo alive but not growing?
3.3.4 Reduced dormancy ( Simpson, 1990 ). Dormancy assists the seed in withstanding severe environmental conditions and also aids in seed dissemination ( Snape et al., 2001 ). When quick seed germination is required during sowing, a high amount of dormancy after harvest is undesirable.
In addition, like in the case of the malt house, quick and uniform germination is essential upon hydration. A high level of dormancy is therefore economically undesirable. In addition, selection against dormancy will result in preharvest sprouting, another undesirable characteristic. Consequently, a balance must be maintained between the two.
Barley dormancy is a quantitative feature governed by a large number of quantitative trait loci (QTL). The most important QTLs are SD1 and SD2 on chromosome 5H. SD1 is situated close to the centromere, while SD2 is situated on the long arm at the distal end.
Scarification, hot water, dry heat, fire, acid and other chemicals, mulch, and light are employed to break the dormancy of seed coats. The presence of germination inhibitors within the seed causes the physiological circumstances producing internal dormancy.
- Using germination-promoting chemicals like as gibberellic acid (GA3) and potassium nitrate, the negative effects of these inhibitors must be reduced so that germination may begin (KNO 3 ).
- Abscisic acid is the most frequent inhibitor (ABA).
- Sugar maple, Norway maple (Acer platanoides L.), planetree maple (Acer pseudoplatanus), European hazel (Corylus avellana L.), white ash (Fraxinus americana L.), apple (Malus pumila Mill.), northern red (Quercus rubra L.), and English oaks contain ABA as an internal inhibitor.
A second form of internal dormancy is induced by an enzyme deficiency, which is necessary for full physiological development. In a species, both seed coat and internal dormancy can be present. The seeds exhibiting this combined dormancy should be handled by first addressing the issues posed by the impermeable seed coat, and then by addressing the internal dormancy.
What is plant germination?
Seeds that know when to germinate – Almost all seeds are in a state of suspended animation, known as dormancy, until the conditions are optimal for germination. Even when exposed to water, oxygen, and the proper temperature, dormancy can cause a seed to delay germination until it receives certain environmental and chemical cues.
- A seed may be latent while still attached to the parent plant (known as primary dormancy), or it may become dormant after separating from the parent (secondary dormancy).
- Dormancy is a method through which plants increase the odds of survival and growth of their progeny.
- It helps seeds to postpone germination until conditions, such as optimal temperature, are present.
It also implies that seeds might delay becoming seedlings until they are at a distance from the parent plant (for instance, by being consumed by animals and expelled elsewhere), so reducing competition with other seeds from the same parent. Lastly, it permits the staggered germination of seeds, so that if poor weather destroys the initial set of seedlings, there will be ‘backup’ seeds.
Several processes cause dormancy, some of which occur outside the embryo (exogenous dormancy) and others within the embryo (physiological dormancy). A hard seed coat is an example of an exogenous dormancy mechanism, since it prevents the seed from absorbing water and occasionally air. The hard seed coat may need to be broken by heat, freezing, or passage through the acidic digestive tract of an animal.
Dormancy can also be caused by elements within the embryo, particularly chemical changes that must occur in the seed prior to germination. Some seeds, for instance, require a time of darkness or light to germinate. Spinifex hirsutus, a plant that grows in the sand dunes of Western Australia, has a greater chance of sprouting when its seeds are buried deep in the dunes, where the sand is more solid and there is more moisture and nutrients; hence, its seeds will not germinate until it is dark.