Dormancy

Source: Wikipedia, the free encyclopedia.
chemical activity.[1]

Dormancy is a period in an

photoperiod and decreasing temperature are used by many plants to predict the onset of winter. Consequential dormancy occurs when organisms enter a dormant phase after adverse conditions have arisen. This is commonly found in areas with an unpredictable climate. While very sudden changes in conditions may lead to a high mortality rate
among animals relying on consequential dormancy, its use can be advantageous, as organisms remain active longer and are therefore able to make greater use of available resources.

Animals

Part of a series on
Animal dormancy

Hibernation

Main article: Hibernation

Hibernation is a mechanism used by many mammals to reduce energy expenditure and survive food shortages over the winter. Hibernation may be predictive or consequential. An animal prepares for hibernation by building up a thick layer of

bats, ground squirrels and other rodents, mouse lemurs, the European hedgehog and other insectivores, monotremes and marsupials. Although hibernation is almost exclusively seen in mammals, some birds, such as the common poorwill
, may hibernate.

Diapause

Main article: Diapause
Further information: Embryonic diapause

Diapause is a predictive strategy that is predetermined by an animal's

mammals such as the roe deer (Capreolus capreolus, the only ungulate with embryonic diapause[citation needed]), in which a delay in attachment of the embryo to the uterine lining ensures that offspring
are born in spring, when conditions are most favorable.

Aestivation

Main article: Aestivation

Aestivation, also spelled estivation, is an example of consequential dormancy in response to very hot or dry conditions. It is common in

crocodiles
.

Brumation

While

heterotherms are described scientifically as hibernating, the way ectotherms such as lizards become dormant in cold is very different, and a separate word was coined for it in the 1920s: brumation.[4] It differs from hibernation in the metabolic processes involved.[5]

Reptiles generally begin brumation in late autumn (more specific times depend on the species). They often wake up to drink water and return to "sleep". They can go for months without food. Reptiles may eat more than usual before the brumation time but eat less or refuse food as the temperature drops. However, they do need to drink water. The brumation period is anywhere from one to eight months depending on the air temperature and the size, age, and health of the reptile. During the first year of life, many small reptiles do not fully brumate, but rather slow down and eat less often. Brumation is triggered by a lack of heat and a decrease in the hours of daylight in winter, similar to hibernation.

Plants

In plant physiology, dormancy is a period of arrested plant growth. It is a survival strategy exhibited by many plant species, which enables them to survive in harsh conditions and climates where part of the year is unsuitable for growth, such as winter or dry seasons.

Many plant species that exhibit dormancy have a

sympodially
growing orchids:

Annual life cycle of sympodially growing orchids with dormancy after completion of new growth/pseudobulb, e.g., Miltonia, or Odontoglossum
Annual life cycle of sympodially growing orchids with dormancy after blooming, e.g., Cycnoches ventricosum, Dendrobium nobile, or Laelia

Seeds

When a mature and viable

seed coat that prevents water and oxygen from reaching and activating the embryo
. It is a physical barrier to germination, not a true form of dormancy (Quinliven, 1971; Quinliven and Nichol, 1971).

Seed dormancy is desired in nature, but the opposite in the agriculture field. This is because agricultural practice desires rapid germination and growth for food whereas in nature, most plants are only capable of germinating once every year, making it favorable for plants to pick a specific time to reproduce. For many plants, it is preferable to reproduce in spring as opposed to fall even when there are similar conditions in terms of light and temperature due to the ensuing winter that follows fall. Many plants and seeds recognize this and enter a dormant period in the fall to stop growing. The grain is a popular example in this aspect, where they would die above ground during the winter, so dormancy is favorable to its seedlings but extensive domestication and crossbreeding has removed most dormancy mechanisms that their ancestors had.[6]

While seed dormancy is linked to many genes, abscisic acid (ABA), a plant hormone, has been linked as a major influencer to seed dormancy. In a study on rice and tobacco plants, plants defective in zeaxanthin epoxidase gene, which are linked to ABA-synthesis pathway. Seeds with higher ABA content, from over-expressing zeaxanthin epoxidase, led to an increased dormancy period while plants with lower numbers of zeaxanthin epoxidase were shown to have a shorter period of dormancy. A simple diagram can be drawn of ABA inhibits seed germination, while gibberellin (GA, also plant hormone) inhibits ABA production and promotes seed germination.[6][7]

Trees

Main article: Vernalization

Typically, temperate woody

perennial plants require chilling temperatures to overcome winter dormancy (rest). The effect of chilling temperatures depends on species and growth stage (Fuchigami et al. 1987).[8] In some species, rest can be broken within hours at any stage of dormancy, with either chemicals, heat, or freezing temperatures, effective dosages of which would seem to be a function of sublethal stress, which results in stimulation of ethylene
production and increased cell membrane permeability.

Dormancy is a general term applicable to any instance in which a tissue predisposed to elongate or grow in some other manner does not do so (Nienstaedt 1966).

conifers (Owens et al. 1977).[10] Physiological dormancy often includes early stages of bud-scale initiation before measurable shoot elongation or before flushing. It may also include late leaf initiation after shoot elongation has been completed. In either of those cases, buds
that appear to be dormant are nevertheless very active morphologically and physiologically.

Dormancy of various kinds is expressed in white spruce (Romberger 1963).[11] White spruce, like many woody plants in temperate and cooler regions, requires exposure to low temperature for a period of weeks before it can resume normal growth and development. This "chilling requirement" for white spruce is satisfied by uninterrupted exposure to temperatures below 7 °C for 4 to 8 weeks, depending on physiological condition (Nienstaedt 1966, 1967).[9][12]

Tree species that have well-developed dormancy needs may be tricked to some degree, but not completely. For instance, if a

Japanese maple (Acer palmatum) is given an "eternal summer" through exposure to additional daylight, it grows continuously for as long as two years. Eventually, however, a temperate-climate plant automatically goes dormant, no matter what environmental conditions it experiences. Deciduous plants lose their leaves; evergreens
curtail all new growth. Going through an "eternal summer" and the resultant automatic dormancy is stressful to the plant and usually fatal. The fatality rate increases to 100% if the plant does not receive the necessary period of cold temperatures required to break the dormancy. Most plants require a certain number of hours of "chilling" at temperatures between about 0 °C and 10 °C to be able to break dormancy (Bewley, Black, K.D 1994).

Short photoperiods induce dormancy and permit the formation of needle primordia. Primordia formation requires 8 to 10 weeks and must be followed by 6 weeks of chilling at 2 °C. Bud break occurs promptly if seedlings are then exposed to 16-hour photoperiods at the 25 °C/20 °C temperature regime. The free growth mode, a juvenile characteristic that is lost after 5 years or so, ceases in seedlings experiencing environmental stress (Logan and Pollard 1976, Logan 1977).[13][14]

Bacteria

Many bacteria can survive adverse conditions such as temperature, desiccation, and antibiotics by forming endospores, cysts, or states of reduced metabolic activity lacking specialized cellular structures.[15] Up to 80% of the bacteria in samples from the wild appear to be metabolically inactive[16]—many of which can be resuscitated.[17] Such dormancy is responsible for the high diversity levels of most natural ecosystems.[18]

Recent research

metabolites to move freely through the cell, which may be helpful in cells transitioning out of dormancy.[19]

Viruses

Further information: Virus latency

Dormancy, in its rigid definition, does not apply to

Herpesviruses, for example, can become latent after infecting the host, and after years they can activate again if the host is under stress or exposed to ultraviolet radiation.[20]

See also

Notes

  1. ISBN 978-0-88192-655-2
    . Retrieved 2009-09-12.
  2. ^ Bert B. Boyer, Brian M. Barnes (1999). "Molecular and metabolic Aspects of Mammalian Hibernation" (PDF). www.colby.edu. Archived from the original (PDF) on 2020-01-25. Retrieved 2017-08-22.
  3. S2CID 5177743
    .
  4. ^ "Reptilian Brumation". Archived from the original on 2012-03-04. Retrieved 2007-12-25.
  5. ^ "Hibernating Mammals and Brumating Reptiles: What's the Difference?". 20 January 2014.
  6. ^
    PMID 22039925
    .
  7. S2CID 27054888
    .
  8. ^ Fuchigami, L. H., Nee, C. C., Tanino, K., Chen, T. H. H., Gusta, L. V., and Weiser, C. J. 1987. "Woody Plant Growth in a Changing Chemical and Physical Environment". Proc. Workshop IUFRO Working Party on Shoot Growth Physiology, Vancouver, British Columbia, July 1987, Lavender, D. P. (Compiler & Ed.), University of British Columbia, Forest Science Department, Vancouver, British  : 265–282.
  9. ^ a b Nienstaedt, H (1966). "Dormancy and dormancy release in white spruce". Forest Science. 12: 374–384.
  10. ISSN 0008-4026
    .
  11. ^ Romberger, J. A. 1963. "Meristems, Growth, and Development in Woody Plants". USDA, Forestry Service, Washington DC, Technical Bulletin 1293. 214 p.
  12. ^ Nienstaedt, H (1967). "Chilling requirements in seven Picea species". Silvae Genetica. 16 (2): 65–68.
  13. ^ Logan, K. T.; Pollard, D. F. W. 1976. "Growth acceleration of tree seedlings in controlled environments at Petawawa". Canadian Forestry Service, Petawawa Forest Experiment Station, Chalk River, Ontario, Information PS-X-62.
  14. ^ Logan, K. T. (1977). "Photoperiodic induction of free growth in juvenile white spruce and black spruce". Bi-monthly Research Notes. 33 (4). Canadian Department of Fishing & Environment, Canadian Forestry Service, Ottawa, Ontario: 29–30.
  15. doi:10.1146/annurev.pp.24.060173.001523
    .
  16. S2CID 40867902
    .
  17. doi:10.4319/lo.1996.41.6.1161
    .
  18. PMID 20231463
    .
  19. ^
    PMID 24361104
    .
  20. PMID 6326635
    .

References
Retrieved from "https://en.wikipedia.org/w/index.php?title=Dormancy&oldid=1215127095"