Editing Diatom (section)

==Behaviour==
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|caption1=''Chaetoceros willei''<br /><small>{{smallcaps|Gran, 1897}}</small>
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|caption2=''Chaetoceros furcillatus'' <small>{{smallcaps|J.W.Bailey, 1856}}</small>
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Most centric and araphid pennate diatoms are [[Motility|nonmotile]], and their relatively dense cell walls cause them to readily sink. [[Plankton]]ic forms in open water usually rely on [[turbulence|turbulent]] mixing of the upper layers of the oceanic waters by the wind to keep them suspended in sunlit surface waters. Many planktonic diatoms have also evolved features that slow their sinking rate, such as spines or the ability to grow in colonial chains.<ref>{{Citation|last1=Padisák|first1=Judit|date=2003|work=Aquatic Biodiversity: A Celebratory Volume in Honour of Henri J. Dumont|pages=243–257|editor-last=Martens|editor-first=Koen|series=Developments in Hydrobiology|publisher=Springer Netherlands|language=en|doi=10.1007/978-94-007-1084-9_18|isbn=9789400710849|last2=Soróczki-Pintér|first2=Éva|last3=Rezner|first3=Zsuzsanna|title=Sinking properties of some phytoplankton shapes and the relation of form resistance to morphological diversity of plankton — an experimental study |url=http://real.mtak.hu/3305/4/1014414.pdf|access-date=4 October 2019|archive-url=https://web.archive.org/web/20180723003836/http://real.mtak.hu/3305/4/1014414.pdf|archive-date=23 July 2018|url-status=dead}}</ref> These adaptations increase their [[Surface-area-to-volume ratio|surface area to volume ratio]] and [[Parasitic drag|drag]], allowing them to stay suspended in the water column longer. Individual cells may regulate [[buoyancy]] via an ionic pump.<ref>{{cite journal|last1=Anderson|first1=Lars W. J.|last2=Sweeney|first2=Beatrice M.|title=Diel changes in sedimentation characteristics of Ditylum brightwelli: Changes in cellular lipid and effects of respiratory inhibitors and ion-transport modifiers1|journal=Limnology and Oceanography|date=1 May 1977|volume=22|issue=3|pages=539–552|doi=10.4319/lo.1977.22.3.0539|language=en|issn=1939-5590|bibcode=1977LimOc..22..539A|doi-access=free}}</ref>

Some pennate diatoms are capable of a type of locomotion called "gliding", which allows them to move across surfaces via adhesive [[mucilage]] secreted through a seamlike structure called the raphe.<ref>{{Cite journal|last1=Poulsen|first1=Nicole C.|last2=Spector|first2=Ilan|last3=Spurck|first3=Timothy P.|last4=Schultz|first4=Thomas F.|last5=Wetherbee|first5=Richard|date=1 September 1999|title=Diatom gliding is the result of an actin-myosin motility system|journal=Cell Motility and the Cytoskeleton |language=en|volume=44|issue=1|pages=23–33|doi=10.1002/(SICI)1097-0169(199909)44:1<23::AID-CM2>3.0.CO;2-D|pmid=10470016|issn=1097-0169}}</ref><ref>{{Cite web|url=http://tolweb.org/raphid_diatoms/125307|title=raphid diatoms|last=Mann|first=David G.|date=February 2010|website=The Tree of Life Web Project|access-date=27 September 2019|archive-date=27 September 2019|archive-url=https://web.archive.org/web/20190927232025/http://tolweb.org/raphid_diatoms/125307|url-status=dead}}</ref> In order for a diatom cell to glide, it must have a solid substrate for the mucilage to adhere to.

Cells are solitary or united into colonies of various kinds, which may be linked by siliceous structures; [[marine mucilage|mucilage]] pads, stalks or tubes; amorphous masses of mucilage; or by threads of [[chitin]] (polysaccharide), which are secreted through strutted processes of the cell.

[[File:Den Norske Nordhavs-expedition, 1876-1878 (1880-1901) (20671468900)-cropped.jpg|thumb|upright=1.5|left|Planktonic diatoms such as ''[[Thalassiosira]]'' sp. (56–62), ''[[Asteromphalus]]'' sp. (63), ''[[Aulacoseira]]'' sp. (64–66), and ''[[Chaetoceros]]'' (see twin image above) often grow in chains, and have features such as spines which slow sinking rates by increasing drag.]]
[[File:Diatom chain.jpg|thumb|upright=1.8| Some ''[[Thalassiosira]]'' diatoms form chain-like colonies, like these collected near the Antarctic peninsula coast by the schooner of the [[Tara expedition|''Tara'' Oceans Expedition]] for plankton research.<br />This projection of a stack of [[Confocal microscopy|confocal images]] shows the diatoms' [[cell wall]] (cyan), [[chloroplast]]s (red), [[DNA]] (blue), [[Biological membrane|membranes]] and [[organelle]]s (green).]]
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===Phytochromes===
Even though light is a crucial part of how diatoms create oxygen for the planet, the organism faces some difficulties when it comes to detecting its energy source. The intensity of light in water lessens as depth increases. Light penetration also greatly differs between coastal and open waters and during the changing seasons. Such factors result in a less efficient photosynthetic conversion, similar to the process of plant photosynthesis,<ref>{{Cite journal |last1=Lu |first1=Danying |last2=Liu |first2=Bin |last3=Ren |first3=Mingjie |last4=Wu |first4=Chao |last5=Ma |first5=Jingjing |last6=Shen |first6=Yamei |date=2021-10-22 |title=Light Deficiency Inhibits Growth by Affecting Photosynthesis Efficiency as well as JA and Ethylene Signaling in Endangered Plant Magnolia sinostellata |journal=Plants |language=en |volume=10 |issue=11 |pages=2261 |doi=10.3390/plants10112261 |doi-access=free |issn=2223-7747 |pmc=8618083 |pmid=34834626|bibcode=2021Plnts..10.2261L }}</ref> as the light becomes dimmer, photsynthesis slows down. However, diatoms possess [[wiktionary:photoreceptor|photoreceptors]], which are light-activated proteins, that aid them in sensing different light wavelengths, such as red light and far-red light, for detecting light in the ocean.<ref>{{Cite journal |last1=Fortunato |first1=Antonio Emidio |last2=Jaubert |first2=Marianne |last3=Enomoto |first3=Gen |last4=Bouly |first4=Jean-Pierre |last5=Raniello |first5=Raffaella |last6=Thaler |first6=Michael |last7=Malviya |first7=Shruti |last8=Bernardes |first8=Juliana Silva |last9=Rappaport |first9=Fabrice |last10=Gentili |first10=Bernard |last11=Huysman |first11=Marie J.J. |last12=Carbone |first12=Alessandra |last13=Bowler |first13=Chris |last14=d’Alcalà |first14=Maurizio Ribera |last15=Ikeuchi |first15=Masahiko |date=2016-03-01 |title=Diatom Phytochromes Reveal the Existence of Far-Red-Light-Based Sensing in the Ocean |journal=The Plant Cell |volume=28 |issue=3 |pages=616–628 |doi=10.1105/tpc.15.00928 |issn=1040-4651 |pmc=4826011 |pmid=26941092|bibcode=2016PlanC..28..616F }}</ref>

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 | image1    = Phaeodactylum tricornutum.png
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It has been demonstrated that diatoms use photoreceptors called [[phytochrome]]s to determine the water’s depth to respond to light signals. Phytochromes can sense red and far-red light and are widely known to be found in both plants and phytoplankton.<ref name=Duchêne2025 /><ref>{{Cite journal |last1=Duanmu |first1=Deqiang |last2=Bachy |first2=Charles |last3=Sudek |first3=Sebastian |last4=Wong |first4=Chee-Hong |last5=Jiménez |first5=Valeria |last6=Rockwell |first6=Nathan C. |last7=Martin |first7=Shelley S. |last8=Ngan |first8=Chew Yee |last9=Reistetter |first9=Emily N. |last10=van Baren |first10=Marijke J. |last11=Price |first11=Dana C. |last12=Wei |first12=Chia-Lin |last13=Reyes-Prieto |first13=Adrian |last14=Lagarias |first14=J. Clark |last15=Worden |first15=Alexandra Z. |date=2014-11-04 |title=Marine algae and land plants share conserved phytochrome signaling systems |journal=Proceedings of the National Academy of Sciences |volume=111 |issue=44 |pages=15827–15832 |doi=10.1073/pnas.1416751111 |doi-access=free |pmc=4226090 |pmid=25267653|bibcode=2014PNAS..11115827D }}</ref> These proteins switch between two states called red-light and far red-light so that the organism can detect and respond to any changes in the perceived underwater light intensity and spectrum.<ref>{{Cite journal |last1=Cheng |first1=Mei-Chun |last2=Kathare |first2=Praveen Kumar |last3=Paik |first3=Inyup |last4=Huq |first4=Enamul |date=2021-06-17 |title=Phytochrome Signaling Networks |journal=Annual Review of Plant Biology |language=en |volume=72 |issue=  1|pages=217–244 |doi=10.1146/annurev-arplant-080620-024221 |issn=1543-5008 |pmc=10988782 |pmid=33756095|bibcode=2021AnRPB..72..217C }}</ref> Since red and far-red light is known to diminish with increasing water depth, many {{who|date=March 2025}} questioned the importance of the phytochromes’ role when it comes to marine life. Analysis of  environmental DNA sequences taken from the [[Tara expedition|Tara Oceans expedition]],<ref>{{Cite journal |last1=Pesant |first1=Stéphane |last2=Not |first2=Fabrice |last3=Picheral |first3=Marc |last4=Kandels-Lewis |first4=Stefanie |last5=Le Bescot |first5=Noan |last6=Gorsky |first6=Gabriel |last7=Iudicone |first7=Daniele |last8=Karsenti |first8=Eric |last9=Speich |first9=Sabrina |last10=Troublé |first10=Romain |last11=Dimier |first11=Céline |last12=Searson |first12=Sarah |date=2015-05-26 |title=Open science resources for the discovery and analysis of Tara Oceans data |journal=Scientific Data |language=en |volume=2 |issue=1 |pages=150023 |doi=10.1038/sdata.2015.23 |issn=2052-4463 |pmc=4443879 |pmid=26029378|bibcode=2015NatSD...250023. }}</ref> as well as the genome data from cultured diatoms which demonstrated that the phytochrome-encoding genes were mostly found in diatoms living in temperate and polar regions in mid-to-high latitudes<ref name=Duchêne2025 /> but such diatom phytochrome genes were not found in diatoms living in tropical waters.

Laboratory experiments with the diatom ''[[Phaeodactylum tricornutum]]'' demonstrated how the diatom phytochromes react to light.<ref name=Duchêne2025 /> Using a yellow fluorescent protein gene controlled by phytochromes  inserted  into the diatom enabled its activity in simulations with deep-water conditions to betracked. This showed that diatoms had developed a reduced sensitivity to far-red light, as well as an increased sensitivity to low-intensity blue and green light, which are more present at greater depths.<ref name=Duchêne2025>{{Cite journal |last1=Duchêne |first1=Carole |last2=Bouly |first2=Jean-Pierre |last3=Pierella Karlusich |first3=Juan José |last4=Vernay |first4=Emeline |last5=Sellés |first5=Julien |last6=Bailleul |first6=Benjamin |last7=Bowler |first7=Chris |last8=Ribera d’Alcalà |first8=Maurizio |last9=Falciatore |first9=Angela |last10=Jaubert |first10=Marianne |date=January 2025 |title=Diatom phytochromes integrate the underwater light spectrum to sense depth |url=https://www.nature.com/articles/s41586-024-08301-3 |journal=Nature |language=en |volume=637 |issue=8046 |pages=691–697 |doi=10.1038/s41586-024-08301-3 |pmid=39695224 |bibcode=2025Natur.637..691D |issn=1476-4687}}</ref>

Removal of the phytochrome gene from the diatom ''[[Thalassiosira pseudonana]]'' grown in a similar deep-water simulation demonstrated that the mutant diatom had a lower photosynthetic efficiency, as well as a reduced photoprotection, compared to the wild-type diatoms with the phytochrome gene,<ref name=Duchêne2025 /> and that when both the mutant and wild-type diatoms were exposed to high white light, there was no difference in reactions. 

With these findings, the authors found that diatom phytochromes respond more to blue and green light in low intensities, unlike the plant phytochromes that respond to red and far-red light.<ref>{{Cite journal |last1=Kreslavski |first1=Vladimir D. |last2=Los |first2=Dmitry A. |last3=Schmitt |first3=Franz-Josef |last4=Zharmukhamedov |first4=Sergey K. |last5=Kuznetsov |first5=Vladimir V. |last6=Allakhverdiev |first6=Suleyman I. |date=2018-05-01 |title=The impact of the phytochromes on photosynthetic processes |url=https://linkinghub.elsevier.com/retrieve/pii/S0005272818300367 |journal=Biochimica et Biophysica Acta (BBA) - Bioenergetics |volume=1859 |issue=5 |pages=400–408 |doi=10.1016/j.bbabio.2018.03.003 |pmid=29545089 |issn=0005-2728}}</ref> They suggest that the diatom phytochromes went through an evolutionary adaptation to acclimate to the violent waters in the open waters of the temperate and polar regions. Since the function of diatom phytochromes is to sense the water depth, it provides the diatoms information that is very advantageous in regions with differing seasons. These photoreceptors play a critical role in helping phytoplankton adjust to environments with limited light, specifically the deep-water environments.