Molecular Biology of Larval Osmoregulation
Halophilic organisms have evolved several diverse strategies in solving problems of osmotic stress. For example, animal and plant halophiles find life can be sustained in large measure by controlling the intracellular osmotic pressure with small molecules. These organisms are referred to as osmoconformers. Somero and colleagues have cogently argued that halophilic osmoconformers utilize a family of organic solutes, termed osmolytes, to passively regulate the intracellular osmotic pressures. This osmotic system is believed to be a more flexible and adaptive mechanism with simpler genetic controls than those proposed for the more “primitive” osmoregulators that are dependent upon genetic control of the mechanics of cell volume. Similarly, halophilic microbes employ small ions as a simple osmolytes to passively control water fluxes across the bacterial cell wall. These bacteria utilize membrane mechanisms that pump into the cell high concentrations of K+ ions. Again, it can be argued that the control of the osmotic system requires a simpler genetic mechanism and, together with the genetic selection for cytosolic proteins having a higher proportion of acidic amino acids, provides for vital subcellular organelles (ribosomes) and enzyme complexes to be functional at salt concentrations in excess of 1 molar. It is obvious that genetic evolution through natural selection has taken a long period of time for this osmotic system to ascertain which of the many changes in DNA sequences needed to code for these proteins was best in coping with widely fluctuating environmental salinites.
KeywordsMDCK Cell Brine Shrimp Salt Gland Sodium Pump Artemia Salina
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