From: Doug Skrecky (oberon@vcn.bc.ca)
Date: Thu May 18 2000 - 07:40:29 MDT
The Journal of Experimental Biology 200: 467-475 1997
James Clegg
Summary: Encysted gastrula embryos of the
crustacean Artemia franciscana have acquired
an array of adaptations that enable them to
survive a wide variety of environmental
extremes. The present paper shows that at
least 60% survive 4 years of continuous
anoxia at physiological temperatures
(20-23 C) when fully hydrated. Although these
embryos appear to carry on a metabolism
during the first day of anoxia, no evidence
for a continuing metabolism throughout the
subsequent 4 years was obtained. During
this period, there were no measurable changes
in the levels of their stored, mobilizable
carbohydrates (trehalose, glycogen, glycerol).
Calculations indicate that, if these carbohydrates
are being utilized at all during anoxia, the rate
is at least 50,000 times lower than the aerobic
rate (lower limit of detection). Indications of
proteolysis during prolonged anoxia were
sought but not found. Under starvation conditions,
the life span of larvae produced from embryos
that had undergone 4 years of anoxia was not
significantly different from that of larvae produced
by embryos that had not experienced anoxia.
thus, all substrates and other metabolites
required to support embryonic development
to the nauplius, as well as endogenous (unfed)
larval growth and molting, are retained during
4 years of anoxia. It is not possible to prove
experimentally that absence of a metabolic
rate in anoxic 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 their structural
integrity in the absence of measurable
biosynthesis and free energy flow and are thus
an exception to a major biological generality.
Potential mechanisms involved in their stability
are discussed.
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