This proposal requests funds to support a study of the mechanisms that regulate the concentration of the intracellular osmolyte, glycine betaine, in response to hyperosmotic stress. Glycine betaine is an extremely common and important osmolyte in a wide variety of species ranging from bacteria to plants and animals. Although a great deal is known about the salinity induced regulation of glycine betaine in bacteria, far less is known about its regulation in plants and even less in animals. We have found that oysters (Cassostrea virginica) from the Atlantic coast utilize substantial amounts of glycine betaine to regulate intracellular osmotic concentrations following hyperosmotic stress. Conspecific oysters from the Chesapeake Bay have much smaller levels of glycine betaine that do not change following high salinity stress, and the Bay oysters are not as salinity tolerant. Since the mitochondrion is usually the site of glycine betaine synthesis, these results suggest that these two populations of oysters differ at the mitochondrial level. This proposal contains experiments designed to test that possibility by comparing several aspects of the mechanism of salinity induced glycine betaine synthesis between the Bay and Atlantic oysters. The results will contribute a great deal to the understanding of glycine betaine regulation and, in addition, should resolve whether the differences between the oyster populations are genetic or environmentally founded.
