Editing Cold hardening

{{Short description|Process by which an organism prepares for cold weather}}
{{lead too short|date=May 2019}}
'''Cold hardening''' is the [[physiological]] and [[biochemical]] process by which an organism prepares for cold weather.

==Plants==
[[File:Ice Storm 2013, Guelph 06.jpg|thumb|Plant covered in snow after an ice storm in 2013, Ontario, Canada]]
[[File:Rosa canina in winter.jpg|thumb|upright|[[Rosa canina]] covered in [[frost]], [[Swabian Jura]]]]
Plants in [[Temperate climate|temperate]] and polar regions adapt to winter and sub zero temperatures by relocating [[nutrient]]s from leaves and shoots to [[storage organ]]s.<ref name=":0">{{Cite journal|last1=Thorsen|first1=Stig Morten|last2=Höglind|first2=Mats|date=2010-12-15|title=Modelling cold hardening and dehardening in timothy. Sensitivity analysis and Bayesian model comparison|journal=Agricultural and Forest Meteorology|volume=150|issue=12|pages=1529–1542|doi=10.1016/j.agrformet.2010.08.001|bibcode=2010AgFM..150.1529T}}</ref> Freezing temperatures induce dehydrative [[Stress (biology)|stress]] on plants, as water absorption in the root and water transport in the plant decreases.<ref name=":1">{{Cite journal|last1=Smallwood|first1=Maggie|last2=Bowles|first2=Dianna J.|date=2002-07-29|title=Plants in a cold climate|journal=Philosophical Transactions of the Royal Society B: Biological Sciences|language=en|volume=357|issue=1423|pages=831–847|doi=10.1098/rstb.2002.1073|issn=0962-8436|pmc=1692998|pmid=12171647}}</ref> Water in and between cells in the plant freezes and expands, causing tissue damage. Cold hardening is a process in which a plant undergoes physiological changes to avoid, or mitigate [[Cell (biology)|cellular]] injuries caused by sub-zero temperatures.<ref name=":0" /> Non-acclimatized individuals can survive −5&nbsp;°C, while an acclimatized individual in the same species can survive −30&nbsp;°C. Plants that originated in the tropics, like [[tomato]] or [[maize]], don't go through cold hardening and are unable to survive freezing temperatures.<ref name=":2">{{Cite journal|last1=McKhann|first1=Heather I.|last2=Gery|first2=Carine|last3=Bérard|first3=Aurélie|last4=Lévêque|first4=Sylvie|last5=Zuther|first5=Ellen|last6=Hincha|first6=Dirk K.|last7=De Mita|first7=S.|last8=Brunel|first8=Dominique|last9=Téoulé|first9=Evelyne|date=2008-01-01|title=Natural variation in CBF gene sequence, gene expression and freezing tolerance in the Versailles core collection of Arabidopsis thaliana|journal=BMC Plant Biology|volume=8|issue=1 |pages=105|doi=10.1186/1471-2229-8-105|issn=1471-2229|pmc=2579297|pmid=18922165 |doi-access=free |bibcode=2008BMCPB...8..105M }}</ref> The plant starts the [[Adaptation (biology)|adaptation]] by exposure to cold yet still not freezing temperatures. The process can be divided into three steps. First the plant perceives low temperature, then converts the [[Signal (biology)|signal]] to activate or repress [[Gene expression|expression]] of appropriate [[gene]]s. Finally, it uses these genes to combat the [[Stress (biology)|stress]], caused by sub-zero temperatures, affecting its living [[Cell (biology)|cells]]. Many of the genes and responses to low temperature [[Stress (biology)|stress]] are shared with other [[abiotic stress]]es, like drought or salinity.<ref name=":1" /> 
 [[Image:Plant cell structure-en.svg|thumb|200px|Schematic of typical plant cell]] When temperature drops, the [[Cell membrane|membrane]] fluidity, [[RNA]] and [[DNA]] stability, and [[enzyme]] activity change. These, in turn, affect [[Transcription (genetics)|transcription]], [[Translation (biology)|translation]], [[Metabolism|intermediate metabolism]], and [[photosynthesis]], leading to an energy imbalance. This energy imbalance is thought to be one of the ways the plant detects low temperature. Experiments on ''[[arabidopsis]]'' show that the plant detects the change in temperature, rather than the [[Thermodynamic temperature|absolute temperature]].<ref name=":1" /> The rate of temperature drop is directly connected to the magnitude of [[calcium]] influx, from the space between cells, into the cell. [[Calcium channel]]s in the [[cell membrane]] detect the temperature drop, and promotes expression of low temperature responsible genes in ''[[alfalfa]]'' and ''[[arabidopsis]]''. The response to the change in [[calcium]] elevation depends on the cell type and [[Stress (biology)|stress]] history. [[Shoot (botany)|Shoot]] tissue will respond more than [[root]] cells, and a cell that already is [[Adaptation|adapted]] to [[Hypothermia|cold stress]] will respond more than one that has not been through cold hardening before. Light doesn't control the onset of cold hardening directly, but shortening of daylight is associated with fall, and starts production of [[reactive oxygen species]] and excitation of [[Photosystem II|photosystem 2]], which influences low-temp [[signal transduction]] mechanisms. Plants with compromised perception of day length have compromised cold acclimation.<ref name=":1" />

Cold increases [[Cell permeability|cell membrane permeability]]<ref>{{Cite book|url=https://archive.org/details/plantsinagricult0000forb|url-access=registration|title=Plants in Agriculture|last1=Forbes|first1=James C.|last2=Watson|first2=Drennan|date=1992-08-20|publisher=Cambridge University Press|isbn=9780521427913|language=en}}</ref> and makes the cell shrink, as water is drawn out when ice is formed in the [[extracellular matrix]] between cells.<ref name=":1" /> To retain the [[surface area]] of the [[cell membrane]] so it will be able to regain its former [[volume]] when temperature rises again, the plant forms more and stronger [[Hechtian strand]]s. These are tubelike structures that connect the [[protoplast]] with the cell wall. When the [[intracellular]] water freezes, the cell will expand, and without cold hardening the cell would rupture. To protect the cell membrane from expansion induced damage, the plant cell changes the proportions of almost all [[lipid]]s in the cell membrane, and increases the amount of total soluble [[protein]] and other cryoprotecting molecules, like sugar and [[proline]].<ref name=":2" />

Chilling injury occurs at 0–10 degrees Celsius, as a result of membrane damage, metabolic changes, and toxic buildup. Symptoms include wilting, water soaking, [[necrosis]], [[chlorosis]], ion leakage, and decreased growth. Freezing injury may occur at temperatures below 0 degrees Celsius. Symptoms of extracellular freezing include structural damage, dehydration, and necrosis. If intracellular freezing occurs, it will lead to death. Freezing injury is a result of lost permeability, plasmolysis, and post-thaw cell bursting.

When spring comes, or during a mild spell in winter, plants de-harden, and if the temperature is warm for long enough – their growth resumes.<ref name=":0" />

==Insects==
Cold hardening has also been observed in [[insect]]s such as the [[Drosophila melanogaster|fruit fly]] and [[diamondback moth]]. These insects use rapid cold hardening to protect against [[cold shock]] during overwintering periods.<ref name=":3">{{Cite journal|title=A rapid cold-hardening process in insects|last1=Chen|first1=CP|last2=Denlinger|first2=DL|journal=Science|last3=Lee|first3=RE|s2cid=39842087|pmid=17800568|doi=10.1126/science.238.4832.1415|volume=238|issue=4832|pages=1415–7|year=1987|bibcode=1987Sci...238.1415L}}</ref><ref>{{Cite journal|title=A rapid cold-hardening response protecting against cold shock injury in Drosophila melanogaster|last1=Lee|first1=RE|last2=Czajka|first2=MC|pmid=2106564|volume=148|journal=J Exp Biol|pages=245–54|year=1990|issue=1 |doi=10.1242/jeb.148.1.245|bibcode=1990JExpB.148..245C }}</ref> [[Overwintering]] insects remain active through the winter while non-overwintering insects [[Insect migration|migrate]] or die. Rapid cold hardening can occur during short periods of undesirable temperatures. The buildup of [[Cryoprotectant|cryoprotective]] compounds such as [[glycerol]] is one mechanism of cold hardening in insects.<ref name=":3" /> Glycerol interacts with other [[cell components]] in order to decrease the insect's permeability to the cold.<ref name=":3" /> When an insect is exposed to cold temperatures, glycerol rapidly accumulates. Glycerol is a [[non-ionic]] [[Kosmotropic|kosmotrope]] forming powerful [[hydrogen bond]]s with [[water molecule]]s. The hydrogen bonds in the glycerol compound compete with the weaker bonds between the water molecules, interrupting ice crystal formation.<ref>{{cite journal | last1 = Duman | first1 = J | year = 2002 | title = The inhibition of ice nucleators by insect antifreeze proteins is enhanced by glycerol and citrate | journal = Journal of Comparative Physiology B | volume = 172 | issue = 2| pages = 163–168 | doi = 10.1007/s00360-001-0239-7 | pmid = 11916110 | s2cid = 22778511 }}</ref> This reaction between glycerol and water has been used as an [[antifreeze]] in the past. Proteins also play a large role in cold hardening. [[Glycogen phosphorylase]] (GlyP) is a key enzyme that increases in comparison to a control group not experiencing cold hardening.<ref>{{cite journal | last1 = Overgaard | first1 = J. | last2 = Sørensen | first2 = J. G. | last3 = Com | first3 = E. | last4 = Colinet | first4 = H. | year = 2013 | title = The rapid cold hardening response of Drosophila melanogaster: Complex regulation across different levels of biological organization | journal = Journal of Insect Physiology | volume = 62 | pages = 46–53 | doi=10.1016/j.jinsphys.2014.01.009| pmid = 24508557 }}</ref> Once warmer temperatures are observed, the process of [[acclimation]] begins, and the increase in the concentrations of glycerol and other cryoprotective compounds is reversed. There is a rapid cold hardening capacity found within certain insects that suggests not all insects can survive a long period of overwintering. Non-[[Diapause|diapausing]] insects can sustain brief temperature shocks but often have a limit to what they can handle before the body can no longer produce enough cryoprotective components.
<nowiki/>[[File:Saving the planet one fruit fly at a time - part 1 (7353498896).jpg|thumb|The common fruit fly]]
In addition to improving insects' survival during cold temperatures, cold hardening also improves the [[organism]]'s performance.<ref name=":4">{{cite journal | last1 = Lee | first1 = R. E. | last2 = Damodaran | first2 = K. | last3 = Yi | first3 = S. X. | last4 = Lorigan | first4 = G. A. | year = 2006 | title = Rapid Cold-Hardening Increases Membrane Fluidity and Cold Tolerance of Insect Cells | journal = Cryobiology | volume = 52 | issue = 3| pages = 459–463 | doi=10.1016/j.cryobiol.2006.03.003| pmid = 16626678 }}</ref> Rapid cold hardening (RCH), one of the fastest cold temperature responses recorded,<ref name=":4" /> allows an insect to quickly adapt to severe weather change without compromising function. ''[[Drosophila melanogaster]]'' (the common fruit fly) is a frequently experimented insect involving cold hardening. An example of RCH enhancing organisms' performance comes from courting and mating within the fruit fly. Fruit flies mate more frequently once RCH has commenced, compared to a control insect group not experiencing RCH.<ref name=":4" /> Most insects experiencing extended cold periods are observed to modify [[membrane lipids]]. Desaturation of [[fatty acid]]s is the most commonly seen modification to the [[cell membrane]].<ref name=":4" /> When fruit flies were observed under a stressful climate, the survival rate increased in comparison to the fly prior to cold hardening.
[[File:Plutella.xylostella.7383.jpg|thumb|The diamondback moth]]
In addition to the common fruit fly, the cold-hardening response of ''[[Diamondback moth|Plutella xylostella]]'' (the diamondback moth) also has been widely studied. While this insect also shows an increase in glycerol and similar cryoprotective compounds, it also shows an increase in [[polyol]]s. These compounds are specifically linked to cryoprotective compounds. The polyol compound is freeze-susceptible and [[Freeze tolerance|freeze tolerant]].<ref name=":5">{{cite journal | last1 = Park | first1 = Y. | last2 = Kim | first2 = Y. | year = 2014 | title = A specific glycerol kinase induces rapid cold hardening of the diamondback moth, Plutella xylostella | journal = Journal of Insect Physiology | volume = 67 | pages = 56–63 | doi=10.1016/j.jinsphys.2014.06.010| pmid = 24973793 | bibcode = 2014JInsP..67...56P }}</ref> Polyols simply act as a barrier within the insect body by preventing [[intracellular]] freezing by restricting the [[extracellular]] freezing likely to happen in overwintering periods.<ref name=":5" /> During the larval stage of the diamondback moth, the significance of glycerol was tested again for validity. The lab injected the larvae with added glycerol and in turn proved that glycerol is a major factor in survival rate when cold hardening. The cold tolerance is directly proportional to the buildup of glycerol during cold hardening.<ref name=":5" />

Cold hardening of insects improves the survival rate of the species and improves function. Once environmental temperature begins to warm up above freezing, the cold hardening process is reversed and the concentrations of glycerol and cryoprotective compounds decrease within the body. This also reverts the function of the insect to pre-cold hardening activity.

== See also ==
*[[Antifreeze protein]]
*[[Cryobiology]]
*[[Cryopreservation]]
*[[Overwintering]]
*[[Hibernation]]

==References==
<references />

{{DEFAULTSORT:Cold Hardening}}
[[Category:Physiology]]
[[Category:Plant physiology]]
[[Category:Cryobiology]]