The term dormancy refers to a series of physiological processes that generally end in the arrest of metabolism, growth and development for variable periods of time. This phenomenon is presented by numerous species of bacteria, fungi, protists, plants and animals, both vertebrates and invertebrates, although for some groups it has never been reported.
Dormancy is an adaptation and survival mechanism that normally occurs in response to extreme environmental conditions such as, for example, seasonal changes where individuals can face extreme temperatures, dehydration, floods, lack of nutrients, among others..
All organisms, both sessile and those with the ability to move freely, face at some point in their life history some limiting condition for their reproduction, growth or survival. Some respond with population phenomena such as migration, while others enter a dormant state.
The factors that trigger the initiation of this process, both external and internal, vary from one species to another, and there may even be important differences between individuals of the same species that are located in geographically different areas..
Here are some characteristics and examples between the process of animals and plants.
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In this group of animals the types of dormancy vary from a small egg to the modified form of an adult. It is classified as quiescence and diapause, depending on the factors involved in the initiation and maintenance of this.
Quiescence refers to all forms that are induced by adverse environmental conditions. Hibernation, estivation, anhydrobiosis (life without water) and cryptobiosis (hidden or hidden life) are forms of quiescence.
The diapause, more than by external conditions, is maintained by internal physiological responses, inherent to each species and individual.
Many species of porifers, cnidarians, flatworms, rotifers, nematodes, tardigrades, arthropods, mollusks, annelids, hemicordates, and chordates present either quiescent or diapaused forms..
Some sponges produce resistance gemmules that help them reestablish full populations once favorable conditions are restored. Certain species of cnidarians produce basal buds or "dormant" sex eggs that can last from weeks to months..
Insects can enter diapause in any of their stages (eggs, larvae, pupae or adults), depending on the species and the habitat they occupy. Myriapods can coil inside small greenhouses on the ground and resist flooding as adult organisms..
Among mollusks it has also been observed that bivalves and prosobranchs enter dormancy by sealing their valves or opening their shells. Bivalves can last several months buried in this way in the sediment.
It is important to mention that dormancy is much more common in species of terrestrial, semi-terrestrial or freshwater invertebrates than in marine species, perhaps due to the relative stability of these environments with respect to terrestrial ones..
In vertebrates the best known cases of dormancy are those of hibernation in mammals such as ursids and rodents, and in birds.
However, much research has recently focused on the dormancy of tumor cell populations of cancer patients, which is closely related to the development of metastases.
As in other animals and plants, in mammals dormancy occurs as an adaptive mechanism to cope with periods of high energy demand but little energy availability in the environment.
It has to do with physiological, morphological and behavioral changes that allow the animal to achieve survival in unfavorable conditions..
The beginning of a hibernation season is characterized by long "shifts" of lethargy during which metabolic rates progressively decline and where body temperature remains only a few degrees above room temperature..
These "lethargy" are interspersed with moments of intense metabolic activity, which manage to increase the body temperature before returning to lethargy. During this period all body functions are reduced: heart rate, respiration, kidney function, etc..
The changes of season prepare the animal for hibernation. The preparation, at the physiological level, is probably achieved by altering the steady state levels of many proteins that serve specific functions of increasing or decreasing the abundance of some mRNAs and their corresponding proteins..
The entry and exit of torpor is more related to reversible and fast metabolic switches, which work more instantaneously than changes in the control of gene expression, transcription, translation or stability of products.
The best known cases of dormancy in plants correspond to the dormancy of seeds, tubers and buds, which are characteristic of plants subjected to seasonality..
Unlike dormancy in animals, plants enter dormancy according to temperature, length of photoperiod, quality of light, temperature during light and dark periods, nutritional conditions, and water availability. It is considered a “hereditary” property since it is also genetically determined.
This phenomenon occurs in many trees and includes the annual loss and renewal of leaves. Trees without leaves during winter are said to be dormant or dormant.
The terminal buds, protected by the cataphiles, are those that subsequently give rise to the new leaves and foliar primordia.
These buds form about two months before active growth ceases and leaves are lost. Unlike animals, in plants photosynthetic, respiratory, transpiration and other physiological activities continue throughout the year, the only thing that truly stops is growth.
The wavelengths of light (red and far red) seem to play a very important role in the establishment and breakdown of dormancy in the buds, as well as the accumulation of the hormone abscisic acid (ABA).
Seed dormancy is very common in wild plants, as it gives them the ability to survive natural disasters, decrease competition between individuals of the same species, or prevent germination in the wrong season..
In seeds this process is controlled by the regulation of gene expression, enzymatic activity and accumulation of growth regulators, with a fundamental role of ABA. This hormone accumulates in the seeds and is believed to be synthesized by the endosperm and the embryo, rather than by the plant that gives rise to the seed..
During dormancy the seeds are resistant to long periods of desiccation. Proteins have been determined LATE-EMBRYOGENESIS ABUNDANT (LEA) appear to act as protectors of other proteins needed during periods of desiccation.
In the tubers there is also dormancy. The meristems of these structures are under arrest in the G1 phase of the cell cycle, prior to DNA synthesis. The release of this arrest is dependent on many cyclin-dependent kinases and their downstream targets..
ABA and ethylene are required for the beginning of dormancy in tubers, but only AVA is necessary to maintain dormancy. In this state, the tubers have low levels of auxin and cytokinin, which are thought to participate in its breakdown and subsequent germination..
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