Effect of osmotic shock on the redox system in plasma membrane of Dunaliella salina

Abstract

The unicellular halotolerant alga Dunaliella salina had the ability to oxidize NADH and reduce Fe(CN)63-. The redox reactions were to some extent stimulated by slight hyperosmotic shock (2.0 mol/L →2.6 mol/L NaCl), but markably inhibited by abrupt hyperosmotic shock (2.0 mol/L → 3.5 mol/L NaCl) and hypoosmotic shock (2.0 mol/L → 1.0 mol/L NaCl; 2.0 mol/L → 0.67 mol/L NaCl). With the adaptation of algal cells to osmotic shock by accumulating or degrading intracellular glycerol, the plasmalemma redox activities were also restored. The O2 uptake stimulated by NADH could be promoted by FA and SHAM. Hypoosmotic shock increases the basal respiration rate of alga cells, but weakened the stimulating effects of NADH, FA and SHAM on O2 uptake. On the other hand, hyperosmotic shock reduced the basal respiration rate, but relatively enhanced the above effects of NADH, FA and SHAM. H+ extrusion of alga cells was inhibited by NADH and stimulated by Fe(CN)63-. Vanadate and DES could inhibit H+ efflux, but had little effect in the presence of NADH and Fe(CN)63-. Both hyper-and hypoosmotic shock stimulated H+ extrusion. This effect could be totally inhibited by vanadate and DES, but almost unaffected by 8-hydroxyquinoline. It was suggested that H+-ATPase probably played a more important role in H+ extrusion and osmoregulation under the conditions of osmotic shock.