Active, Irreversible Accumulation of Extreme Levels of H 2 SO 4 in the Brown Alga, Desmarestia

Abstract

The brown algae Desmarestia ligulata var. ligulata (Lightf.) Lamour., and D. viridis (Mull.) Lamour., accumulate H(2)SO(4) until their average internal pH is 0.5 to 0.8. A related species, D. aculeata (L.) Lamour., does not accumulate acid. The H(2)SO(4) accumulation is accompanied by a reduction in the K(+) and Cl(-) content, presumedly to maintain osmotic balance. Measurements of the membrane potential and H(+) and SO(4) (2-) concentrations indicate that both ions are accumulated in the vacuole against their electrochemical potential gradients.The internal pH remains constant in all three species over the growing season, despite striking changes in the algal morphology. The pH is not affected by periods of darkness of up to 34 hours. Sulfate accumulated in the vacuoles appears to be trapped there since incubation of D. ligulata for up to 10 days in sulfate-free medium resulted in little loss of either vacuolar sulfate or H(+). Although the uptake of H(2)SO(4) into the vacuole must require energy, the maintenance of the vacuolar H(2)SO(4) may be due to the impermeability of the tonoplast, with little necessity for continued expenditure of energy.