Encysted embryos (cysts) of the brine shrimp, Artemia provide an excellent model system for the s... more Encysted embryos (cysts) of the brine shrimp, Artemia provide an excellent model system for the study of biochemical adaptation to environmental extremes. Here, we describe an experiment in which cysts of A. franciscana from the San Francisco Bay (SFB), California, U.S.A., were inoculated into experimental ponds in the Mekong Delta region of Vietnam where water temperatures are much higher than the SFB. Cysts produced in each of three successive growing seasons (1996–1998) were collected and examined in the laboratory for resistance to high temperature and relative contents of three stress proteins (Hsp-70, artemin and p26). Thermal adaptation took place rapidly, during the first growing season. The increase in thermal tolerance was reflected in an overall increase in stress protein content, compared to SFB cysts used for the initial inoculation. Also examined were cysts of A. tibetiana collected from a lake on the high plateau of Tibet, PR China, almost 4.5 km above sea level. These cysts were very sensitive to high temperatures, and contained much lower levels of all stress proteins examined, compared to A. franciscana cysts from SFB and Vietnam. Cysts of A. sinica, collected from a hypersaline lake in Inner Mongolia, PR China, were examined in the same fashion and found to be similar to SFB cysts in terms of thermal resistance and stress protein content. The harsh environments in which Artemia are found, and the great diversity of its habitats, world-wide, provide excellent opportunities to relate the ecological setting of an organism to the underlying physiological and biochemical processes enabling its survival.
Mouse L-929 cells were subjected to increasing concentrations of sorbitol, which remove cell wate... more Mouse L-929 cells were subjected to increasing concentrations of sorbitol, which remove cell water and reduce volume osmotically. The rate of lactate production from glucose was significantly higher in osmotically perturbed cells than in controls, both in monolayers and in suspensions. L cells can apparently use sorbitol as a glycolytic substrate; however, studies using other solutes (trehalose and sucrose) and permeabilized cells showed that the major effect of scrbitol on glycolysis in intact cells is mediated through a reduction in cell water content and volume. It is possible to explain some of these results by an increase in the chemical potentials of dissolved components of the glycolytic pathway caused by water loss; however, the relationship between water loss and glycolytic rate increase in not a simple linear one, suggesting that the situation is more complex than would result merely from increased concentrations of pathway components. Whatever the complete explanation might be, these studies show that glycolysis continues in an orderly fashion in cells that have lost about 85% of their original water content, suggesting that the operation of this pathway is not unduly sensitive to events taking place in the bulk aqueous phase.
Cells of encysted embryos of Artemia franciscana, the brine shrimp, are among the most resistant ... more Cells of encysted embryos of Artemia franciscana, the brine shrimp, are among the most resistant of all animal cells to extremes of environmental stress. We focus here on their ability to survive continuous anoxia for periods of years, during which their metabolic rate is undetectable. We asked whether their impressive tolerance was reflected in changes at the ultrastructural level. The ultrastructure of encysted embryos previously experiencing 38 days and 3.3 years of anoxia was compared with those not undergoing anoxia (controls). Rough endoplasmic reticulum was abundant in anoxic embryos, in spite of the absence of protein biosynthesis in their cells. Other cytoplasmic changes had occurred in the anoxic cells, but overall their structure was remarkably intact, in view of their 3 years of continuous anoxia. A major difference was the presence of abundant electron-dense granules in the nuclei of anoxic embryos; these were present but rare in nuclei of controls. Biochemical fractionation and Western immunoblotting confirmed previous observations that substantial amounts of the small heat shock/α-crystallin protein (p26) translocated into nuclei of anoxic embryos. We have no evidence that the dense granules contain this protein, but that remains a possibility. In contrast, and contrary to expectation, proteins of the hsp70 and 90 families did not undergo anoxia-induced nuclear translocation, an unusual result since such translocations have been widely observed in cells from a variety of organisms.
Encysted embryos (cysts) of the brine shrimp, Artemia provide an excellent model system for the s... more Encysted embryos (cysts) of the brine shrimp, Artemia provide an excellent model system for the study of biochemical adaptation to environmental extremes. Here, we describe an experiment in which cysts of A. franciscana from the San Francisco Bay (SFB), California, U.S.A., were inoculated into experimental ponds in the Mekong Delta region of Vietnam where water temperatures are much higher than the SFB. Cysts produced in each of three successive growing seasons (1996–1998) were collected and examined in the laboratory for resistance to high temperature and relative contents of three stress proteins (Hsp-70, artemin and p26). Thermal adaptation took place rapidly, during the first growing season. The increase in thermal tolerance was reflected in an overall increase in stress protein content, compared to SFB cysts used for the initial inoculation. Also examined were cysts of A. tibetiana collected from a lake on the high plateau of Tibet, PR China, almost 4.5 km above sea level. These cysts were very sensitive to high temperatures, and contained much lower levels of all stress proteins examined, compared to A. franciscana cysts from SFB and Vietnam. Cysts of A. sinica, collected from a hypersaline lake in Inner Mongolia, PR China, were examined in the same fashion and found to be similar to SFB cysts in terms of thermal resistance and stress protein content. The harsh environments in which Artemia are found, and the great diversity of its habitats, world-wide, provide excellent opportunities to relate the ecological setting of an organism to the underlying physiological and biochemical processes enabling its survival.
Mouse L-929 cells were subjected to increasing concentrations of sorbitol, which remove cell wate... more Mouse L-929 cells were subjected to increasing concentrations of sorbitol, which remove cell water and reduce volume osmotically. The rate of lactate production from glucose was significantly higher in osmotically perturbed cells than in controls, both in monolayers and in suspensions. L cells can apparently use sorbitol as a glycolytic substrate; however, studies using other solutes (trehalose and sucrose) and permeabilized cells showed that the major effect of scrbitol on glycolysis in intact cells is mediated through a reduction in cell water content and volume. It is possible to explain some of these results by an increase in the chemical potentials of dissolved components of the glycolytic pathway caused by water loss; however, the relationship between water loss and glycolytic rate increase in not a simple linear one, suggesting that the situation is more complex than would result merely from increased concentrations of pathway components. Whatever the complete explanation might be, these studies show that glycolysis continues in an orderly fashion in cells that have lost about 85% of their original water content, suggesting that the operation of this pathway is not unduly sensitive to events taking place in the bulk aqueous phase.
Cells of encysted embryos of Artemia franciscana, the brine shrimp, are among the most resistant ... more Cells of encysted embryos of Artemia franciscana, the brine shrimp, are among the most resistant of all animal cells to extremes of environmental stress. We focus here on their ability to survive continuous anoxia for periods of years, during which their metabolic rate is undetectable. We asked whether their impressive tolerance was reflected in changes at the ultrastructural level. The ultrastructure of encysted embryos previously experiencing 38 days and 3.3 years of anoxia was compared with those not undergoing anoxia (controls). Rough endoplasmic reticulum was abundant in anoxic embryos, in spite of the absence of protein biosynthesis in their cells. Other cytoplasmic changes had occurred in the anoxic cells, but overall their structure was remarkably intact, in view of their 3 years of continuous anoxia. A major difference was the presence of abundant electron-dense granules in the nuclei of anoxic embryos; these were present but rare in nuclei of controls. Biochemical fractionation and Western immunoblotting confirmed previous observations that substantial amounts of the small heat shock/α-crystallin protein (p26) translocated into nuclei of anoxic embryos. We have no evidence that the dense granules contain this protein, but that remains a possibility. In contrast, and contrary to expectation, proteins of the hsp70 and 90 families did not undergo anoxia-induced nuclear translocation, an unusual result since such translocations have been widely observed in cells from a variety of organisms.
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