Akinete

[[File:Dolichospermum smithii - akinete.jpg|thumbnail|Intercalary located akinete of ''Dolichospermum smithii'']] [[File:Gloeotrichia - akineta.jpg|thumbnail|Terminally located akinete of ''Gloeotrichia'']] [[File: Mikrofoto.de-Blutregenalgen 3.jpg|thumb|right|Akinetes, also termed "cysts", of ''Haematococcus'']] An '''akinete''' is an enveloped, thick-walled, non-motile, dormant cell formed by both cyanobacteria and algae. Cyanobacterial akinetes are mainly formed by filamentous, heterocyst-forming members under the order Nostocales and Stigonematales.<ref name=adams>{{cite journal |last1=Adams |first1=David |last2=Duggan |first2=Paula |date=Aug 1999 |title=Heterocyst and akinete differentiation in cyanobacteria |journal=New Phytol |volume=144 |pages=23–28 |doi=10.1046/j.1469-8137.1999.00505.x|doi-access=free }}</ref><ref>Moore, R. et al. (1998) ''Botany.'' 2nd Ed. WCB/McGraw Hill. {{ISBN|0-697-28623-1}}</ref><ref name=sukenik>{{cite journal |last1=Sukenik |first1=Assaf |last2=Beardall |first2=John |last3=Hadas |first3=Ora |title=Photosynthetic Characterization of Developing and Mature Akinetes Ofaphanizomenon Ovalisporum(Cyanoprokaryota)1 |date=July 2007 |journal= Journal of Phycology |volume=43 |issue=4 |pages=780–788 |doi=10.1111/j.1529-8817.2007.00374.x|bibcode=2007JPcgy..43..780S |s2cid=85200692 }}</ref><ref name=sukenik2015>{{cite journal |last1=Sukenik |first1=Assaf |last2=Maldener |first2=Iris |last3= Delhaye |first3=Thomas |date=September 2015|title=Carbon assimilation and accumulation of cyanophycin during the development of dormant cells (akinetes) in the cyanobacterium Aphanizomenon ovalisporum |journal=Front. Microbiol. |volume=6 |page=1067 |doi=10.3389/fmicb.2015.01067 |pmid=26483781 |pmc=4586427 |doi-access=free }}</ref> Eukaryotic microalgae also produce akinetes, such as ''Haematococcus''.<ref>{{cite journal|doi=10.4490/algae.2023.38.3.9 |title=The description of ''Haematococcus privus'' sp. nov. (Chlorophyceae, Chlamydomonadales) from North America |date=2023 |last1=Buchheim |first1=Mark A. |last2=Silver |first2=Ashley |last3=Johnson |first3=Haley |last4=Portman |first4=Richard |last5=Toomey |first5=Matthew B. |journal=Algae |volume=38 |pages=1–22 |doi-access=free }}</ref>

During akinete formation, cells accumulate and store various essential material, allowing the akinete to serve as a survival structure for up to many years.<ref name=adams /><ref name=sukenik2015 /> The cell akinetes are resistant to cold and desiccation.<ref name=adams /> However, akinetes are not resistant to heat.<ref name=adams /> Once conditions become more favorable for growth, the akinete can then germinate back into a vegetative cell.<ref name=Myers2>{{cite journal |last1=Myers |first1=Jackie |last2=Beardall |first2=John |last3=Allinson |first3=Graeme |date=July 2010 |title=Environmental influences on akinete germination and development in Nodularia spumigena (Cyanobacteriaceae), isolated from the Gippsland Lakes, Victoria, Australia |journal=Hydrobiologia |volume=649 |issue=1 |pages=239–247 |doi=10.1007/s10750-010-0252-5|s2cid=23052084 }}</ref> Increased light intensity, nutrient availability, oxygen availability, and changes in salinity are important triggers for germination.<ref name=Myers2 />

In cyanobacteria, akinetes usually develop in strings with each cell differentiating after another and this occurs next to heterocysts if they are present.<ref name=adams /> Development usually occurs during stationary phase and is triggered by unfavorable conditions such as insufficient light or nutrients, temperature, and saline levels in the environment.<ref name=adams /><ref name=sukenik2015 /> In comparison to vegetative cells, akinetes are generally larger.<ref name=sukenik2015 /><ref name=2suk>{{cite journal|last1=Sukenik|first1=Assaf|last2=Kaplan-Levy|first2=Ruth|last3=Mark|first3=Jessica|date=March 2012|title=Massive multiplication of genome and ribosomes in dormant cells (akinetes) of Aphanizomenon ovalisporum (Cyanobacteria)|journal=The ISME Journal|volume=6|issue=3|pages=670–679|doi=10.1038/ismej.2011.128|pmc=3280138|pmid=21975597}}</ref> This is associated with the accumulation of nucleic acids which is important for both dormancy and germination of the akinete.<ref name=2suk /> Despite being a resting cell, it is still capable of some metabolic activities such as photosynthesis, protein synthesis, and carbon fixation, albeit at significantly lower levels.<ref name=sukenik />

Akinetes can remain dormant for extended periods of time. Studies have shown that some species could be cultured that from akinetes were 18 and 64 years old.<ref>David Livingstone & G.H.M. Jaworski (1980) The viability of akinetes of blue-green algae recovered from the sediments of Rostherne Mere, British Phycological Journal, 15:4, 357-364, DOI: 10.1080/00071618000650361</ref> Akinete formation also influences the perennial blooms of cyanobacteria.<ref name=myers>{{cite journal |last1=Myers |first1=Jackie |last2=Beardall |first2=John |date=Aug 2011 |title=Potential triggers of akinete differentiation in Nodularia spumigena (Cyanobacteriaceae) isolated from Australia |journal=Hydrobiologia |volume=671 |issue=1 |pages=165 |doi=10.1007/s10750-011-0714-4 |s2cid=7949386 }}</ref>

In algae, akinetes form when environmental signals indicate impending change unfavorable to growth, such as the arrival of winter. Like cyanobacterial akinetes, they accumulate storage materials, but also develop thick cell walls and suspend active metabolism.<ref name=Graham/> When conditions improve, the akinete germinates via the cell wall breaking open.<ref name=Graham>{{Cite book|last1=Graham|first1=J.E.|last2=Wilcox|first2=L.W.|last3=Graham|first3=L.E.|title=Algae, 2nd Edition|publisher=Pearson|year=2009|isbn=9780321603128|pages=616}}</ref>

== References == {{reflist}}

Category:Cell biology Category:Cyanobacterial cells Category:Cyanobacteria Category:Algae