Intracellular p H Regulates Transitions Between Dormancy and Development of Brine Shrimp ( Artemia salina ) Embryos

The intracellular pH (pH(i))of encysted gastrula-stage embryos of the brine shrip, Artemia, as previously shown by in vivo phosphorus-31 nuclear magnetic resonance spectroscopy, increases by more than 1 unit during arousal from cryptobiotic dormancy and decreases by the same amount during reinduction of dormancy. These changes in pH(i) are now shown to be a fundamental regulator of the transitions between dormancy and metabolism: acidification of activated embryo pH(i) by more than 1 unit with carbon dioxide induced a state comparable to natural dormancy, while alkalinization of dormant embryo pH(i) with the weak base ammonia terminated natural dormancy. This demonstration of pH(i)-mediated regulation of cryptobiotic dormancy extends the known scope for pH(i) as a regulator of development to include multicellular stages of the metazoan life cycle.