Akinete

File:Dolichospermum smithii - akinete.jpg]]

File:Gloeotrichia - akineta.jpg]]

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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.{{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 }}Moore, R. et al. (1998) Botany. 2nd Ed. WCB/McGraw Hill. {{ISBN|0-697-28623-1}}{{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 }}{{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 }} Eukaryotic microalgae also produce akinetes, such as Haematococcus.{{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 }}

During akinete formation, cells accumulate and store various essential material, allowing the akinete to serve as a survival structure for up to many years. The cell akinetes are resistant to cold and desiccation. However, akinetes are not resistant to heat. Once conditions become more favorable for growth, the akinete can then germinate back into a vegetative cell.{{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 }} Increased light intensity, nutrients availability, oxygen availability, and changes in salinity are important triggers for germination.

In cyanobacteria, akinetes usually develop in strings with each cell differentiating after another and this occurs next to heterocysts if they are present. 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.

In comparison to vegetative cells, akinetes are generally larger.{{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}} This is associated with the accumulation of nucleic acids which is important for both dormancy and germination of the akinete. 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.

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.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 Akinete formation also influences the perennial blooms of cyanobacteria.{{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 }}

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. When conditions improve, the akinete germinates via the cell wall breaking open.{{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}}