{{short description|Vanadium-rich blood cell found in tunicates}} A '''vanadocyte''' is a specialized type of blood cell found in ascidians (tunicates). These cells are notable for their high levels of vanadium (concentrations 10<sup>7</sup> higher than that of seawater), which is typically a metabolic poison in other contexts.<ref name="Michibata2002">{{cite journal |last1=Michibata |first1=Hitoshi |last2=Uyama |first2=Taro |last3=Ueki |first3=Tatsuya |last4=Kanamori |first4=Kan |title=Vanadocytes, cells hold the key to resolving the highly selective accumulation and reduction of vanadium in ascidians |journal=Microscopy Research and Technique |date=15 March 2002 |volume=56 |issue=6 |pages=421–434 |doi=10.1002/jemt.10042 |pmid=11921344 |s2cid=15127292 |url=http://ir.lib.hiroshima-u.ac.jp/files/public/0/22/20141016115442843522/MicroscopResTech_56_421-434_2002.pdf |archive-date=17 March 2020 |access-date=8 August 2019 |archive-url=https://web.archive.org/web/20200317132408/https://ir.lib.hiroshima-u.ac.jp/files/public/0/22/20141016115442843522/MicroscopResTech_56_421-434_2002.pdf |url-status=dead }}</ref><ref name="Stoecker1978">{{cite journal |last1=STOECKER |first1=DIANE |title=Resistance of a Tunicate to Fouling |journal=The Biological Bulletin |date=December 1978 |volume=155 |issue=3 |pages=615–626 |doi=10.2307/1540795|jstor=1540795 |url=https://www.biodiversitylibrary.org/part/21615 }}</ref>
==Structure and description== Vanadocytes are specialized blood cells found in marine tunicates. These cells are 8-13 μm in size and the cytoplasm contains many acidic globules, termed "vanadophores".<ref name="Botte1979">{{cite journal |last1=Botte |first1=L. |last2=Scippa |first2=S. |last3=de Vincentiis |first3=M. |title=Ultrastructural localization of vanadium in the blood cells of Ascidiacea |journal=Experientia |date=September 1979 |volume=35 |issue=9 |pages=1228–1230 |doi=10.1007/BF01963306|pmid=488290 |s2cid=33061777 }}</ref> These cells are one of several types found in the ascidian circulatory system and are abundant in the blood.<ref name="Stoecker1978"/><ref name="Michibata2002"/>
The cells are described as highly distinctive, with little variation between species. They have a circular outline that decays into a rosette form upon desiccation, with several inclusions that almost entirely fill the cell. The cell has a greenish color, varying from dark apple to scarcely perceptible, due to their vanadium complexes.<ref name="Carlson1975">{{cite journal |last1=Carlson |first1=Robert |title=Nuclear Magnetic Resonance Spectrum of Living Tunicate Blood Cells and the Structure of the Native Vanadium Chromogen |journal=PNAS |date=1975 |volume=72 |issue=6 |pages=2217–2221 |pmc=432728 |jstor=64680 |pmid=1056026 |doi=10.1073/pnas.72.6.2217 |bibcode=1975PNAS...72.2217C |doi-access=free }}</ref><ref name="Webb1939">{{cite journal |last1=Webb |first1=D.A. |title=Observations on the blood of certain ascidians, with special reference to the biochemistry of vanadium |journal=Journal of Experimental Biology |date=1939 |volume=16 |issue=4 |pages=499–523 |doi=10.1242/jeb.16.4.499 |url=https://jeb.biologists.org/content/16/4/499 |accessdate=24 June 2019|doi-access=free }}</ref>
These green cells are not, as was initially believed, symbiotic zooxanthellae, although ascidians are known to have such symbiotes elsewhere.<ref name="Webb1939"/>
==Chemistry== Vanadocytes are of interest to biologists and chemists because they contain high levels of vanadium and vacuole of sulfuric acid with acid mass fraction as high as 9 wt%, both of which are typically toxic to living creatures.<ref name="Webb1939"/> Additionally, the vanadium complex itself is unstable, found almost exclusively in the air-oxidizable, +3 oxidation state.<ref name="Carlson1975"/>
==Function== The function of vanadocytes is still unclear.<ref name="Michibata2002"/> It has been proposed that the vanadocyte transports and processes nutrients, contributes to the polysaccharide external tunic, or serves as a defense mechanism. It is unlikely that the vanadium complex serves as an oxygen transport mechanism because it is unable to reversibly bind oxygen.<ref name="Carlson1975"/>
Research into their utility as anti-biofouling (allelopathic) mechanisms concluded that the high acidity and high vanadium levels function to significantly reduce epizoic recruitment and predation.<ref>{{cite journal |last1=Stoecker |first1=Diane |title=Relationships between chemical defense and ecology in benthic ascidians |journal=Marine Ecology Progress Series |date=1980 |volume=3 |pages=257–265|doi=10.3354/meps003257 |bibcode=1980MEPS....3..257S |doi-access=free }}</ref><ref>{{cite journal |last1=Stoecker |first1=Diane |title=Distribution of acid and vanadium in ''Rhopalaea birkelandi'' tokioka |journal=Journal of Experimental Marine Biology and Ecology |date=1980 |volume=48 |issue=3 |pages=277–281|doi=10.1016/0022-0981(80)90082-9 |bibcode=1980JEMBE..48..277S }}</ref>
==References== {{Reflist}}
Category:Ascidiacea Category:Blood cells