Types of Dormancy

Dormancy is a well-known behavioural and physiological state of both animals and plants, characterised by inactivity and a reduced metabolic rate. Torpor, like dormancy, refers to inactivity or lethargy. Dormancy or torpor can involve a wide range of physiological states in response to a variety of stimuli, including low temperature, high temperature, a lack of water, or a lack of food. It can be a short-term event (24 hours), occur for a few days in a row, or last an entire season or even many years. Dormancy can also be associated with a developmental halt (diapause). Cryptobiosis which means hidden life is a more extreme state than dormancy in that there is almost no detectable activity or metabolism. It is most common in lower vertebrates and is frequently a seasonal survival strategy against cold or desiccation.

Dormancy

Dormancy is the inability of living organisms to grow or develop. They temporarily stop or slow down their metabolic activity. It is also possible to argue that when living creatures are not actively growing, they enter a deep slumber. Plants, as we all know, are incapable of self-protection or survival in the absence of water. As a result, they go dormant to avoid adverse climatic and temperature fluctuations.

Seed Dormancy

Seed dormancy is defined as a dormant state in which seeds cannot germinate despite the presence of optional environmental conditions.

Bud Dormancy

Bud dormancy is a temporary halt to most physiological activity and growth that can be reactivated.

This could be a reaction to environmental factors like seasonality, extreme heat, drought, or extreme cold. The resumption of bud growth marks the end of bud dormancy.

Methods of Breaking Seed Dormancy

The following are the various methods for breaking dormancy:

The natural breaking of Seed Dormancy

Dormancy ends when the embryo is exposed to an appropriate environment, such as adaptive moisture and temperature. The smoothing action of the natural agents such as microorganisms, temperature, and abrasion by the digestive tract of birds and animals that feed on these seeds causes the seed coat of many species to become permeable. Other natural methods are as follows:

• The over-ripening period has come to an end.
• Inhibitors found in the seed coat are leached.
• Cold, heat, and light are used to inactivate inhibitors.
• Excess and highly concentrated solutes from the seeds are leached.
• Growth hormones are produced, which can counteract the effects of inhibitors.

Artificial Overcoming of Seed Dormancy

The following are the artificial methods for breaking seed dormancy:

• Hot water action for the termination of waxes, surface inhibitors, and other substances.
• Seed coat rupturing via filing, chipping, or threshing machines.
• Depending on the type of seed dormancy, exposure to heat, cold, or light.
• Hydraulic pressure is applied for 5 to 20 minutes to weaken the tough seed coats.
• To remove all traces of the mineral acid, seed coats are treated with concentrated sulphuric acid.

Treatment to break dormancy in seeds

There are distinct treatments for overcoming dormancy, which is further classified as follows:

Seed coat treatment

These treatments soften or crack a hard seed coat, making it permeable to water or gases. Scarification is the name given to this process. Chemical or physical treatments are both possible.

Embryo treatments

Stratification

Seeds are incubated at a low temperature over a moist layer before being transferred to a temperature suitable for germination.

High-temperature treatment

Incubation at 40-50 °C for a few hours to a few days may help some species overcome dormancy. For example, rice seeds that have been treated with hot water at 40°C for at least 4 hours.

Chemical treatments

In induced germination growth regulators, plant growth regulators or other chemicals can be used.

Causes of Seed Dormancy

The following factors contribute to seed dormancy:

Mechanically resistant seed coat

The growing embryo is unable to exit the seed coat due to the tough and mechanical seed coat. For instance, mustard (Brassica), peppergrass (Lepidium), and so on.

Impermeable seed coat

Many plants have hard seed coats that are impermeable to water, gases, and chemicals. As a result, the seed never germinates and remains dormant. Chenopodium, Xanthium, Brassica alba, and other plants are examples.

Rudimentary and poorly developed embryos

At the time of seed germination, the embryos of some seeds are still immature and rudimentary. Ginkgo biloba, Eranthis hyemalis, and other examples

Dormant embryos

Although the embryos in many species of apple, peach, cherry, pines, peas, and so on are fully developed in ripe seed, the seeds fail to germinate even when the environmental conditions are ideal. This is due to the embryo’s physiological immaturity. When they go through the after-ripening process, they can germinate.

Germination inhibitors

The presence of compounds known as inhibitors has a significant impact on seed germination. Some natural germination inhibitors can be found in fruit pulp, seed coat, endosperm, embryos or structures surrounding them, and so on (e.g.tomatoes, glumes of Oats, etc.) Abscisic acid, phenolic acids, short-chain fatty acids, coumarin, and other important chemical germination inhibitors

Specific light requirement

Certain plant species’ seeds, such as Lactona Sativa and Nicotiana tabacum, have specific light requirements for germination.

Types of Dormancy

Dormancy can be classified in a variety of ways. There are two important classification bases.

1. source
2. nature

Depending on the source, the following types of dormancy exist:

Exogenous

External conditions outside the embryo cause exogenous dormancy.

Physical

Seed coat dormancy is another name for physical dormancy. The seed coat is hard in this type of dormancy, preventing the seed from absorbing water and gases. Olive, peach, plum, apricot, and other fruits are examples.

Mechanical

Mechanical dormancy occurs when seed radicle growth is restricted by seed covering, resulting in seed dormancy. As an example, consider walnut.

Chemical

Seed coat dormancy is another name for physical dormancy. The seed coat is hard in this type of dormancy, preventing the seed from absorbing water and gases. Olive, peach, plum, apricot, and other fruits are examples.

Endogenous

The internal conditions of the embryo cause endogenous dormancy.

Types of dormancy depending on nature

 Primary dormancy

The seed is released from the plant, which is already dormant, during primary dormancy.

Secondary dormancy

Secondary dormancy occurs when a plant’s released seed becomes dormant as a result of environmental conditions.

Conclusion

Dormancy is a well-known behavioural and physiological state of both animals and plants, characterised by inactivity and a reduced metabolic rate. Torpor, like dormancy, refers to inactivity or lethargy. . It is also possible to argue that when living creatures are not actively growing, they enter a deep slumber. . As a result, they go dormant to avoid adverse climatic and temperature fluctuations. Dormancy is the inability of living organisms to grow or develop. They temporarily stop or slow down their metabolic activity. Dormancy ends when the embryo is exposed to an appropriate environment, such as adaptive moisture and temperature. Hydraulic pressure is applied for 5 to 20 minutes to weaken the tough seed coats. These treatments soften or crack a hard seed coat, making it permeable to water or gases. Scarification is the name given to this process. Mechanical dormancy occurs when seed radicle growth is restricted by seed covering, resulting in seed dormancy. As an example, consider walnut.