EMBRYOS OF ARTEMIA-FRANCISCANA SURVIVE 4 YEARS OF CONTINUOUS ANOXIA -THE CASE FOR COMPLETE METABOLIC-RATE DEPRESSION

Encysted gastrula embryos of the crustacean Artemia franciscana have a cquired an array of adaptations that enable them to survive a wide var iety of environmental extremes. The present paper shows that at least 60% survive 4 years of continuous anoxia at physiological temperatures (20-23 degrees C) when fully hydrated, Although these embryos appear to carry on a metabolism during the first day of anoxia, no evidence f or a continuing metabolism throughout the subsequent 4 years was obtai ned, During this period, there were no measurable changes in the level s of their stored, mobilizable carbohydrates (trehalose, glycogen, gly cerol), Calculations indicate that, if these carbohydrates are being u tilized at all during anoxia, the rate is at the least 50 000 times lo wer than the aerobic rate (lower limit of detection), Indications of p roteolysis during prolonged anoxia were sought but not found, Under st arvation conditions, the life span of larvae produced from embryos tha t had undergone 4 years of anoxia was not significantly different from that of larvae produced by embryos that had not experienced anoxia, T hus, all substrates and other metabolites required to support embryoni c development to the nauplius, as well as endogenous (unfed) larval gr owth and molting, are retained during 4 years of anoxia, It is not pos sible to prove experimentally the absence of a metabolic rate in anoxi c embryos under physiological conditions of hydration and temperature, Nevertheless, on the basis of the results presented here, I will make the case that the anoxic embryo brings its metabolism to a reversible standstill, Such a conclusion requires that these embryos maintain th eir structural integrity in the absence of measurable biosynthesis and free energy flow and are thus an exception to a major biological gene rality, Potential mechanisms involved in their stability are discussed .