The effect of AgNO3 on the bioenergetic processes and the ultrastructure of Chlorella and Dunaliella cells exposed to different saline conditions

The effect of AgNO3, an inhibitor of the H+ pump in the plasma membrane, on the bioenergetic processes and on the ultrastructure of the microalgae Chlorella vulgaris (salt sensitive) and Dunaliella maritima (salt resistant) was examined under varying salt concentrations. Differences between them were observed in changes of the cellular energy metabolism depending on their salt sensitivity and the inhibition of the H+ pump activity. A decrease was observed in the rates of heat production (about 45%), O2 uptake (greater than 40–50% of the control) and particularly photosynthesis (more than 80%) in Chlorella cells under the simultaneous action of NaCl and AgNO3. Dunaliella cells showed small to moderate rate increases for heat production (less than 7%), O2 uptake (10–15%) and O2 evolution (40%) in higher salt concentrations and under the action of AgNO3. The production of active oxygen species was studied as an early unspecific response of microalgal cells to possible unfavorable conditions, including salt stress. The amount of superoxide formed by the Dunaliella cells was higher than that by the Chlorella cells. However, Ag+ ions increased the generation rate of superoxide radicals considerably in both Chlorella and Dunaliella cells. The electron microscopy showed that changes of the algal ultrastructure of cells exposed to the action of Ag+ ions were connected with the observed physiological changes and to a large extent with the alteration of the bioenergetic processes in them.