Effect of anoxia on nucleotide metabolism in encysted embryos of the brine shrimp

Abstract

When encysted embryos of the brine shrimp, Artemia salina , are maintained in an oxygen-free saline medium, morphogenesis and carbohydrate metabolism are arrested, but nucleotide metabolism continues in an orderly manner. Although anoxia inhibits the utilization of diguanosine 5′-tetraphosphate (Gp 4 G) in encysted embryos compared to embryos exposed to air only, Gp 4 G is metabolized under anaerobic conditions and appears to be the primary source of phosphate-bond energy necessary to maintain the viability of anoxia-arrested embryos. We found that during 4 months of anoxia approximately 50% of the total available phosphate-bond energy in the embryo, mainly in the form of Gp 4 G, is utilized. Also, during prolonged periods of anoxia the adenosine nucleotide pools are depleted, but guanosine nucleotide metabolism continues. When anoxia is terminated by aeration all nucleotide pools, except for the diguanosine nucleotides, return to levels found in control embryos at the time of hatching. In addition, the rate of recovery of the nucleotide pools correlates well with the delay, if any, in the resumption of morphogenesis. Finally, as development of Artemia embryos approaches hatching, N 2 treatment appears to have a diminishing effect upon the control of guanosine nucleotide metabolism.