Release of intracellular glycerol and pore formation in Dunaliella tertiolecta exposed to hypotonic stress

Abstract

When Dunaliella tertiolecta cells, previously cultured in a 0.5 M NaCl medium, were resuspended in a 0.25 NaCl medium, about 50% of the intracellular glycerol was lost within 2 min. A corresponding amount of glycerol appeared in the medium, while other organic solutes, such as amino acids and sugars, were not detected. These results indicate that intracellular glycerol is rapidly released without significant concomitant cell damage. Rubidum, in the case of rubidium-loaded cells, was also rapidly released to the medium in response to hypotonic shock. Gramicidin, dimers of which form stable membrane pores, caused rapid release of intracellular glycerol, while the ionophore, valinomycin, had no effect. When 0.5 M NaCl-grown cells were resuspended in 0.25 M NaCl medium, intracellular trapping of 14C-glycerol occurred but not of 14C-glucose, 14C-sucrose, or 14C-glycine. However, when 0.5 M NaCl-grown cells were resuspended in 0.05 M NaCl medium, intracellular trapping of small amounts of, 14C-glucose, 14C-sucrose, or 14C-glycine, in addition to considerable amounts of 14C-glycerol, occurred. These results indicate that abrupt hypotonic shocks cause transient formation of small nonspecific pores in the plasma membrane of D. tertiolecta cells and that intracellular glycerol is released to the medium through such nonspecific transient pores. Key words: Dunaliella, hypotonic shock, glycerol release, rubidum, pore formation.