Functional polarity of the tentacle of the sea anemone Anemonia viridis: role in inorganic carbon acquisition.
The oral epithelial layers of anthozoans have a polarized morphology: photosynthetic endosymbionts live within endodermal cells facing the coelenteric cavity and are separated from the external seawater by the ectodermal layer and the mesoglea. To study if this morphology plays a role in the supply of inorganic carbon for symbiont photosynthesis, we measured the change in pH and the rate of OH- (H+) fluxes induced by each cell layer on a tentacle of the sea anemone Anemonia viridis. Light-induced pH increase of the medium bathing the endodermal layers led to the generation of a transepithelial pH gradient of approximately 0.8 pH units across the tentacle, whereas darkness induced acidification of this medium. The light-induced pH change was associated with an increase of total alkalinity. Only the endodermal layer was able to induce a net OH- secretion (H+ absorption). The light-induced OH- secretion by the endodermal cell layer was dependent on the presence of HCO3- in the compartment facing the ectoderm and was sensitive to several inhibitors of ion transport. [14C] HCO3- incorporation into photosynthates confirmed the ectodermal supply, the extent of which varied from 25 to > 90%, according to HCO3- availability. Our results suggest that the light-induced OH- secretion by the endodermal cell layer followed the polarized transport of HCO3- and its subsequent decarboxylation within the endodermal cell layer. This polarity may play a significant role both in inorganic carbon absorption and in the control of light-enhanced calcification in scleractinian corals.
Furla
P
P
Observatoire Océanologique Européen, Centre Scientifique de Monaco, Principality of Monaco.
Bénazet-Tambutté
S
S
Jaubert
J
J
Allemand
D
D
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D002244:Carbon / Q000378:metabolism*; D004707:Endoderm / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D006878:Hydroxides / Q000378:metabolism; D007700:Kinetics; D008027:Light; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis; D012615:Sea Anemones / Q000033:anatomy & histology* / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology
D001639:Bicarbonates; D006878:Hydroxides; D002244:Carbon; D000584:Amiloride; D012964:Sodium; D010100:Oxygen