THE METABOLIC STATUS OF QUIESCENT AND DIAPAUSE EMBRYOS OF ARTEMIA FRANCISCANA (KELLOGG)
J.S. Clegg, S.A. Jackson
Abstract:
Encysted embryos of the brine shrimp, Artemia franciscana are remarkably resistant to environmental stress. About 35 % of post-diapause (activated) embryos hatched into normal larvae after undergoing five years of continuous anoxia. We consider the evidence that these exceptional anoxic longevities result from the ability of these embryos to bring their metabolism to a reversible standstill. Post-anoxic embryos showed an overall reduction in the level op protein synthesis compared to controls (no anoxia) but the synthesis of a major protein was up-regulated in post-anoxic embryos, suggesting a typical "stress response". Diapause embryos produced in field cultures in south Vietnam were kept in the laboratory for 17 months with very few breaking diapase "spontaneously" after initial processing. Treatments that terminate diapause (dehydration, H2O2 and NH4Cl) resulted in different levels of hatching. Diapause embryos may also enter a reversibly ametabolic state since no changes in trehalose and glycogen contents were observed between one and 17 months of diapause. In addition, larvae hatched from embryos after one month of of diapause had the same longevity under starvation conditions as those hatched from embryos in diapause for 17 months, indicating the retention of all substrates and other metabolites required for larval growth and molting. The synthesis of trehalose during development of diapause embryos from fertilized eggs was examined using laboratory cultures of adults. Trehalose accumulation does not become appreciable until the gastrula enters developmental diapause, but its concentration increases for several days after diapause gastrulae are released from females. That result reinforces previous evidence that the onset of developmental diapause does not coincide with a cessation of embryonic metabolism.
(Bodega Marine Laboratory, University of California at Davis, P.O. Box 247, Bodega Bay, CA 94923, USA)