Modulation of Na⁺/H⁺ Antiporter Activity by Extreme pH and Salt in the Halotolerant Alga Dunaliella salina

Abstract

The effect of different growth conditions on the activity of the Na+/H+ antiporter in Dunaliella salina has been investigated. Adaptation of D. salina cells to ammonia at alkaline pH or to high NaCI concentrations is associated with a pronounced increase in the plasma membrane Na+/H+ exchange activity. The enhanced activity is manifested both in vivo, by stimulation of Na+ influx into intact cells in response to internal acidification, and in vitro, by a larger 22Na accumulation in plasma membrane vesicles in response to an induced pH gradient. Kinetic analysis shows that the stimulation does not result from a change of the Km for Na+ but from an increase in the Vmax. In contrast, adaptation of cells to a high LiCI concentration (0.8 M) depresses the activity of the Na+/H+ antiporter. Adaptation to ammonia is also associated with a large increase of three polypeptide bands in purified plasma membrane preparations, indicating that they may compose the antiporter polypeptides. These results suggest that adaptation to ammonia or to high salinity induces overproduction of the plasma membrane Na+/H+ antiporter in Dunaliella.was described in roots of the halophyte Atriplex numularia (5), but it has not been well characterized. However, a vacuolar Na+/H+ antiporter was found and characterized in several plant species, and it was reported that an increase in salt concentration can induce an increased antiporter activity (1,4,7 It is demonstrated that the activity of the plasma membrane Na+/H+ antiporter is overproduced in cells adapted to ammonia or to high NaCl and depressed by adaptation to LiCl.

Osmotic responses of Dunaliella to the changes of salinity

“…In D. salina , the polypeptide played role as the Na + /H + antiporter in adapting to high NaCl. The activity of the Na + /H + antiporter activity increased when the cells were grown at increasing NaCl concentrations (Katz et al, 1992). A 13 kDa protein (p13) accumulated obviously when D. salina cells were subjected to drastic hyperosmotic shock (Table 1).…”

Approaches to improve stress tolerance using molecular genetics

“…Increased antiporter activity on the tonoplast has been observed by treatment or adaptation to salt (Garbarino & DuPont 1989;Blumwald & Poole 1987). In the halotolerant alga Dunaliella salina, the plasma membrane antiporter activity is increased in cells adapted to high NaCl and putative components of the antiporter have been identified (Katz, Pick & Avron 1992).…”

Ion Homeostasis in NaCl Stress Environments

“…Induction of plasma membrane Nat/H+ antiport activities by NaCl occurred in the halotolerant alga Dunaliella salina (Katz et al, 1992) and the halophyte Atriplex nummularia (Hassidim et al, 1990). The H+-translocating activities of the plasma membrane ATPase increased in response to NaCl treatment in tobacco cells and roots of the halophyte A. nummularia (Braun et al, 1986;Watad et al, 1991).…”