A vanadocyte is a specialized type of blood cell found in ascidians (tunicates). These cells are notable for their high levels of vanadium (concentrations 107 higher than that of seawater), which is typically a metabolic poison in other contexts.[1][2]
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".[3] These cells are one of several types found in the ascidian circulatory system and are abundant in the blood.[2][1]
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.[4][5]
These green cells are not, as was initially believed, symbiotic zooxanthellae, although ascidians are known to have such symbiotes elsewhere.[5]
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.[5] Additionally, the vanadium complex itself is unstable, found almost exclusively in the air-oxidizable, +3 oxidation state.[4]
Function
The function of vanadocytes is still unclear.[1] 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.[4]
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.[6][7]
References
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