Involvement of the Plasma Membrane ATPase in the Osmoregulatory Mechanism of the Alga Dunaliella salina

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Abstract
The unicellular halotolerant alga Dunaliella salina recovers normally from a hypertonic shock even when suspended in NaCl and buffer only. Furthermore, addition of Cu2+, valinomycin and KCl, or permeable ions such as methyltriphenylphosphonium or thiocyanate, do not affect the recovery. However, treatment with two specific inhibitors of the plasma membrane adenosine triphosphatase (ATPase), diethylstilbestrol, or vanadate, fully inhibit the recovery. The inhibition is manifested by the inability of the cells to both synthesize glycerol and return to their original volume. The inhibitions are nonlethal, reversible and equally effective in the dark or the light. Since the plasma membrane ATPase is the only enzyme known to be inhibited by both diethylstilbestrol and vanadate, it is concluded that its activity is essential for the recovery of Dunaliella from a hypertonic shock. Mechanisms by which the plasma membrane ATPase may participate in the activation of glycerol production in the algae are discussed.