Editing Abiotic stress (section)

=== Drought stress ===
Drought stress, defined as naturally occurring water deficit, is a main cause of crop losses in agriculture. This is because water is essential for many fundamental processes in plant growth.<ref name=":02">{{Cite journal|last1=González-Villagra|first1=Jorge|last2=Rodrigues-Salvador|first2=Acácio|last3=Nunes-Nesi|first3=Adriano|last4=Cohen|first4=Jerry D.|last5=Reyes-Díaz|first5=Marjorie M.|date=March 2018|title=Age-related mechanism and its relationship with secondary metabolism and abscisic acid in Aristotelia chilensis plants subjected to drought stress|journal=Plant Physiology and Biochemistry|volume=124|pages=136–145|doi=10.1016/j.plaphy.2018.01.010|pmid=29360623|issn=0981-9428|url=http://www.locus.ufv.br/handle/123456789/19426|doi-access=free|bibcode=2018PlPB..124..136G }}</ref> It has become especially important in recent years to find a way to combat drought stress. A decrease in precipitation and consequent increase in drought are extremely likely in the future due to an increase in global warming.<ref name=":1"/> Plants have come up with many mechanisms and adaptations to try and deal with drought stress. One of the leading ways that plants combat drought stress is by closing their [[stoma]]ta. A key hormone regulating stomatal opening and closing is [[abscisic acid]] (ABA). Synthesis of ABA causes the ABA to bind to receptors. This binding then affects the opening of ion channels, thereby decreasing [[turgor pressure]] in the stomata and causing them to close. Recent studies by Gonzalez-Villagra, et al., have shown how ABA levels increased in drought-stressed plants (2018). They showed that when plants were placed in a stressful situation, they produced more ABA to try to conserve any water they had in their leaves.<ref name=":02" /> Another extremely important factor in dealing with drought stress and regulating the uptake and export of water is [[aquaporin]]s (AQPs). AQPs are integral membrane proteins that make up channels. These channels' main job is the transport of water and other essential [[solute]]s. AQPs are both transcriptionally and post-transcriptionally regulated by many different factors such as ABA, GA3, pH and Ca<sup>2+</sup>; and the specific levels of AQPs in certain parts of the plant, such as roots or leaves, helps to draw as much water into the plant as possible.<ref>{{Cite journal|last1=Zargar|first1=Sajad Majeed|last2=Nagar|first2=Preeti|last3=Deshmukh|first3=Rupesh|last4=Nazir|first4=Muslima|last5=Wani|first5=Aijaz Ahmad|last6=Masoodi|first6=Khalid Zaffar|last7=Agrawal|first7=Ganesh Kumar|last8=Rakwal|first8=Randeep|date=October 2017|title=Aquaporins as potential drought tolerance inducing proteins: Towards instigating stress tolerance|journal=Journal of Proteomics|volume=169|pages=233–238|doi=10.1016/j.jprot.2017.04.010|pmid=28412527|issn=1874-3919}}</ref> By understanding the mechanisms of both AQPs and the hormone ABA, scientists will be better able to produce drought-resistant plants in the future.

A study by Tombesi et al., found that plants which had previously been exposed to drought were able to minimize water loss and decrease water use.<ref name=":1">{{Cite journal|last1=Tombesi|first1=Sergio|last2=Frioni|first2=Tommaso|last3=Poni|first3=Stefano|last4=Palliotti|first4=Alberto|date=June 2018|title=Effect of water stress "memory" on plant behavior during subsequent drought stress|journal=Environmental and Experimental Botany|volume=150|pages=106–114|doi=10.1016/j.envexpbot.2018.03.009|bibcode=2018EnvEB.150..106T |s2cid=90058393|issn=0098-8472}}</ref> They found that plants which were exposed to drought conditions actually changed the way they regulated their stomata and what they called "hydraulic safety margin" so as to decrease the vulnerability of the plant. By changing the regulation of stomata and subsequently the transpiration, plants were able to function better when less water was available.<ref name=":1" />