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

Abstract

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 (μmol/gfw)--declined from a control value of 36 μmol/gfw to about 4 μmol/gfw. Concomitantly, average glycogen levels increased from a control value of 29 μmol/gfw to a steady-state level of 62 μmol/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 μmol/ min · mg protein after 30 h of exposure to 20°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.

Formulation of a Basal Medium for Primary Cell Culture of the Marine Sponge Hymeniacidon perleve

“…Organic particles, microalgae, and marine microorganism are food for field-growing sponges. Sorbitol was primary carbon source for the sponge Eunapius fragilis in the diapause period to protect it from cold and dry conditions (27). Pyruvic acid was also considered as a useful carbon source for the sponge S. domuncula (4).…”

The Effects of Elevated Osmotic Concentration on Control of Germination in the Gemmules of Freshwater SpongesEunapius fragilisandAnheteromeyania ryderi

“…The osmolytes responsible for these observations and the effects they have on cell division and respiration have not, as yet, been examined. In a previous article (Loomis et al 1996), we showed that sorbitol was present in the cells of quiescent Eunapius fragiUs gemmules and that the concentration of sorbitol decreased dramatically during the early stages of germination. Further, we showed that the reduction of sorbitol is due to an increase in the activity of sorbitol dehydrogenase and that the sorbitol is most likely being converted to glycogen.…”

“…Diapause and quiescence are characterized by a greatly reduced metabolic rate, as demonstrated by low rates of oxygen consumption and metabolic heat production. Both heat dissipation and oxygen consumption rates were very low in diapausing and quiescent gemmules of £ fragiiis (Loomis et al 1996), and these rates increased steadily during germination, reaching 600% of the starting level by the time ceils emerged from the gemmule. To test the hypothesis that increased osmotic concentration maintains the gemmules in quiescence, we measured the effects of increased osmotic concentration on the rate of oxygen consumption in both E. fragiiis and A. ryderi.…”

“…The calculated sorbitol concentration in the cells of the gemmules of E. fragilis is approximately 134 mM. The concentration of sorbitol decreases by approximately 90% during germination and reaches a minimum at 50 h (Loomis et al 1996). The concentration of sorbitol drops below 50 mM by 18 h after initiation of germination.…”

“…Using HPLC, 'H NMR, and "C NMR, we previously identified the major component of the ethanol-soluble extract in Eunapius fragilis as sorbitol (Loomis et al 1996}. The calculated sorbitol concentration in the cells of the gemmules of E. fragilis is approximately 134 mM.…”