Abstract
The brown algae Desmarestia ligulata var. ligulata (Lightf.) Lamour., and D. viridis (Mull.) Lamour., accumulate H2SO4 until their average internal pH is 0.5 to 0.8. A related species, D. aculeata (L.) Lamour., does not accumulate acid. The H2SO4 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 SO42− 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 H2SO4 into the vacuole must require energy, the maintenance of the vacuolar H2SO4 may be due to the impermeability of the tonoplast, with little necessity for continued expenditure of energy.
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Selected References
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