Zinc Is Probably Not Accumulated as Zinc Sulfide, and Is Co-Released with Glutathione to the Culture Medium, in the Marine Alga Ulva compressa

Abstract

The mechanisms involved in zinc (Zn) accumulation in response to a sulfur donor (NaHS) and a sulfur acceptor (hypotaurine) were analyzed in the marine alga Ulva compressa. The alga was cultivated with 10 μM of Zn, with 10 μM of Zn and increasing concentrations of NaHS for 0 to 7 days, and with 10 μM of Zn and 500 μM of hypotaurine for 5 days. The levels of glutathione (GSH) and phytochelatins (PCs) were also analyzed as well as the levels of transcripts encoding metallothioneins (MTs). Results showed that the level of intracellular Zn mainly decreased in response to 50, 100 or 200 μM of NaHS, compared with the control treated with 10 μM of Zn, and decreased in response to hypotaurine. The level of GSH, PCs (PC2, PC3 and PC4) as well as the level of transcripts encoding MTs did not parallel the level of intracellular Zn, in response to Zn alone or Zn with a sulfur donor. Zn and GSH were released to the culture medium; their release did not increase in response to a sulfur donor, and PCs were not detected in the culture medium. Thus, zinc is probably not accumulated as Zn sulfide (ZnS) and it is co-released to the culture medium with GSH in the marine alga U. compressa.