Growth is an increase in the size or weight of a cell, organ, or organism. An increment in size can occur without growth as absorption of water by a flaccid cell. In a similar manner, during the germination of a seed, there is an actual fall of dry weight though the size and fresh weight increase. So, growth is explained as a permanent or irreversible increase in dry weight, mass, or volume of a cell, size, organ, or organism. Plant growth occurs in three Phases – formative, enlargement, and differentiation. The formative phase has also termed the phase of cell formation or cell division or meristematic phase. The enlargement phase is also known as the phase of cell elongation and the differentiation phase is also known as the phase of maturation.
Seed Dormancy
Seed dormancy can be explained as the state in which seeds are stopped from germinating even under favorable conditions like temperature, water, light, gas, seed coats, and other mechanical restrictions. The major reason behind this condition is that they need a period of rest before being capable of germination. These conditions may range from days to months and even years. These conditions are the merger of light, water, heat, gases, seed coats, and hormone structures.
Dormant seeds are unable to germinate in a specified period of time under a combination of environmental factors that are normally helpful to the germination of non-dormant seeds.
Types of Seed Dormancy
The following are the types of seed dormancy:
- Innate dormancy: In this dormancy, even if the conditions suitable for seedling growth are supplied, the seeds are incapable of germination. This inability to germinate may be due to the reason the embryo is immature at the time of dispersal in certain species.
- Enforced dormancy: It is the condition of seeds, which is unable to germinate due to an environmental bridle which includes, a sufficient amount of moisture, oxygen, light, and a suitable temperature.
- Induced dormancy: Induced dormancy occurs when the seed has imbibed water but has been placed under extremely adverse conditions for germination. Eventually, the seed fails to germinate even under more favorable conditions.
Causes of Seed Dormancy
The main causes or reasons for seed dormancy are as follows:
- Temperature
- Light
- Period after ripening
- Hard seed coat
- Presence of high-concentrate solutes
- Impermeability of seed coat to water
- Impermeability of seed coat to oxygen
- Immaturity of the seed embryo
- Mechanically resistant seed coat
- Germination of inhibitors
Methods of Breaking Seed Dormancy
The different methods of breaking seed dormancy are as follows:
Natural Breaking of Seed Dormancy
The nature of dormancy stops when the embryo gets a suitable environment such as adaptive moisture and temperature. The seed coat that exists in several species becomes permeable due to the breaking of smoothing action of natural agents like temperature, microorganisms, and abrasion by the digestive tract of birds and animals that nourish on these seeds. Some other natural methods include:
- Deactivation of inhibitors by the supply of cold, heat, and light.
- The over-ripening period is completed.
- Leaching of the surplus and highly concentrated solutes from the seeds.
- Creation of growth hormones that can neutralize the effect of inhibitors.
- Leaching of inhibitors found in the seed coat.
Artificial Reduction of Seed Dormancy
A few of the artificial methods used for breaking seed dormancy are as follows:
- Applying hydraulic pressure for 5 to 20 minutes in purpose to weaken the tough seed coats.
- Splitting of seed coats by filling, chipping, or threshing through machines.
- Action with hot water for the ending of waxes, surface inhibitors, etc.
- Exposure to heat, cold, or light, be dependent on seed dormancy.
Treatment to Break Dormancy in Seeds
Some of the different treatments to defeat dormancy are further divisible into the following groups:
Embryo Treatments
- Stratification: The incubation of seeds at a suitable low temperature over a moist layer before conveying them to a temperature worthy of germination.
- High-temperature treatment: Incubation at 40-50° C for a few hours to a few days may result in defeating dormancy in some species. For example, rice seeds are treated with hot water at 40° C for at least 4 hours.
Seed Coat Treatment
The seed coat treatment makes hard seed coats permeable to water or gases either by cracking or softening. This process is known as scarification. The treatment can be in the nature of chemical or physical.
Chemical Treatments
Plant growth regulators or other chemicals can be used in induced germination growth controllers.
Importance of Seed Dormancy
- Seed dormancy permits the seeds to continue to be in suspended animation without any harm during cold or high summer temperatures and even under drought conditions.
- It is known to be the natural process of preservation.
- It is helpful in the dispersion of seeds through unfavorable environments.
- It helps in the storage of seeds for later use by animals or man.
- Dormancy induced by the inhibitors present in the seed coats is highly advantageous to desert plants.
Role of Hormones in Seed Dormancy
Abscisic acid (ABA) is the only plant hormone known for the maintenance of seed dormancy, it acts through a gene expression network including the transcription factor Abscisic Acid Insensitive 3 (ABI3). However, other phytohormone pathways in retort to internal and environmental signals stays an important question. The plant growth hormone auxin, which acts as a versatile cause in several developmental processes, also plays a crucial role in seed dormancy in Arabidopsis. Moreover, seed dormancy and germination are controlled by numerous other plant hormones, such as gibberellin, ethylene, and brassinosteroid. GA provokes seed germination whereas, the involvement of ABA is in the establishment and maintenance of seed dormancy. Cytokinin assists cotyledon greening by repressing the inhibitory effect of ABA.
FAQs on Seed Dormancy
Question 1: What do you mean by seed dormancy?
Answer:
Seed dormancy is an evolutionary adaptation that stops seeds to germinate under favorable conditions.
Question 2: Which two hormones affect dormancy?
Answer:
The two hormones which affect seed dormancy are Ethylene and Abscisic acid.
Question 3: What are the advantages of seed dormancy?
Answer:
Seed dormancy assures high rates of survival in tropical regions despite water stress.
Question 4: What are the differences between seed viability and seed dormancy?
Answer:
Seed viability determines whether the seed will grow or not whereas seed dormancy is related to the prevention of seeds from germination.
Question 5: What are the types of seed dormancy?
Answer:
Dormancy is of three types: innate, enforced, and induced.