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The Biological Bulletin, Vol 191, Issue 3 393-401, Copyright © 1996 by Marine Biological Laboratory

DEVELOPMENT

Carbohydrate Mobilization During Germination of Post-Diapausing Gemmules of the Freshwater Sponge Eunapius fragilis

S. H. Loomis, L. F. Ungemach, B. R. Branchini, S. C. Hand and P. E. Fell
Department of Zoology, Connecticut College, New London, Connecticut 06320

Post-diapausing gemmules of the freshwater sponge Eunapius fragilis were found to contain sorbitol and glycogen as their primary carbohydrates. The sorbitol probably acts to increase the tolerance of the gemmules to freezing and desiccation. During germination, average sorbitol levels--measured as micromoles of sorbitol per gram of fresh weight of gemmule tissue ({mu}mol/gfw)--declined from a control value of 36 {mu}mol/gfw to about 4 {mu}mol/gfw. Concomitantly, average glycogen levels increased from a control value of 29 {mu}mol/gfw to a steady-state level of 62 {mu}mol/gfw. It is probable that glycogen is being synthesized at the expense of sorbitol. The breakdown of sorbitol was associated with an increase in the activity of sorbitol dehydrogenase from undetectable levels in dormant gemmules to a maximum of 0.2 {mu}mol/ min {middot} mg protein after 30 h of exposure to 20{deg}C. Aldose reductase activity remained constant throughout germination. These data support the hypothesis that the decrease in sorbitol levels is the result of an increase in the rate of catabolism by sorbitol dehydrogenase. The total activity of glycogen synthase did not change during germination; however, the activity of glucose-6-phosphate-dependent glycogen synthase was about 18 times greater than the activity of glucose-6-phosphate-independent glycogen synthase. Total glycogen phosphorylase activity increased from about 1.6 nmol/min.mg protein to 3.6 nmol/min.mg protein during germination. At the same time, however, the percentage of glycogen phosphorylase a decreased from almost 100% to about 84%. This decrease would attenuate the apparent increase in activity. cAMP levels remained constant throughout germination. The observed changes in the level of glycogen in the gemmules are not simply due to changes in the activity of either glycogen phosphorylase or glycogen synthase.


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J. Podrabsky and S. Hand
The bioenergetics of embryonic diapause in an annual killifish, austrofundulus limnaeus
J. Exp. Biol., January 10, 1999; 202(19): 2567 - 2580.
[Abstract] [PDF]


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