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Cytochemical studies of vanadium, tunichromes and related substances in ascidians: possible biological significance
Martoja, R.; Gouzerh, P.; Monniot, F. (1994). Cytochemical studies of vanadium, tunichromes and related substances in ascidians: possible biological significance. Oceanogr. Mar. Biol. Ann. Rev. 32: 531-556
In: Oceanography and Marine Biology: An Annual Review. Aberdeen University Press/Allen & Unwin: London. ISSN 0078-3218, more
Peer reviewed article  

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Keywords
    Cytochemistry; Vanadium; Ascidiacea [WoRMS]; Marine

Authors  Top 
  • Martoja, R.
  • Gouzerh, P.
  • Monniot, F.

Abstract
    Vanadium ligands in tunicate blood and test cells have been studied with cytochemical and cytophysical techniques applied to smears and histological sections, in ways that avoided cell fractionation and instrument-related artefacts. Our results support some assertions and contradict others that have been based on physical and biochemical data. In Phallusia fumigata, vanadium is stored in the signet ring cells (SRC), compartment cells (CC), and morula cells (MC) of the blood, and in the ovarian test cells (TC). The metal is mostly found in the MC. The assertion that the MC of Ascidia sydneiensis and Phallusia mammillata lack vanadium is erroneous, probably due to technical artefacts.In the tunichromeless SRC and CC, vanadium is bound to thiol groups, probably of glutathione, and to vanadobin or some other oxygen-donor ligands. The plentiful sulphur in the MC is not bound to vanadium but rather to a vanadium-free water-soluble molecule. In the MC and TC, vanadium and tunichrome are physically separated and the metal is stored as an oxobridged polymeric complex.Our results suggest independent paths of differentiation of the blood and ovarian test cells from undifferentiated cell types: one path would lead to the CC via the SRC, others to the MC and the TC.The MC are probably excretory cells for both the reduced vanadium and its reducing agent (tunichrome or analogues). The function of the SRC and of the CC remains unclear; these cells might act as a reserve. Chemical features of the TC of several tunicate species suggest that these cells make the larval tunic hydrophilic. R. Martoja also proposes that the TC contribute to the formation of ornamental silica deposits and coloured features on the larval tunic's surface.

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