LOOMIS, S.H.*; BETTRIDGE, A.; Connecticut College; Connecticut College: Effects of osmotic pressure on metabolism and cell division in germinating gemmules of the fresh water sponge, Anheteromeyenia ryderi
Many fresh water sponges produce gemmules to survive periods of environmental stress. Gemmules of Anheteromeyenia ryderi are produced year round. Just after production, gemmules are in a state of diapause and only switch to quiescence following a three-month period of vernalization. When quiescent gemmules are warmed to 25�C, new sponge tissue emerges after 72 to 120 hours. During this germination time, archaeocytes within the gemmules begin dividing and differentiating so that at the time of emergence they are ready to develop into adult sponge tissue. Oxygen consumption during germination increases from 0.04 �moles/min/gfw to more than 0.6 �moles/min/gfw. One of the first biochemical events that occurs in the gemmules during germination is a rapid decline in myo-inositol concentration from 1200 nmoles/gfw to about 50 nmoles/gfw. This reduction in myo-inositol can account for observed reduction in the osmotic pressure of gemmules during germination. We tested the hypothesis that increased osmotic pressure could inhibit the germination process by artificially maintaining high intracellular osmotic pressure in the gemmules by exposing them to extracellular solutions of polyethylene glycol. Concentrations of polyethylene glycol above 100 mOsM completely inhibited germination and suppressed oxygen consumption to less than 20 percent of control values. Solutions greater than 50 mOsM polyethylene glycol reduced BrdU incorporation into cells during germination to undetectable levels implying that high osmotic concentration inhibits cell division. These data are consistent with a role for inositol in maintaining sponge gemmules in a quiescent state by keeping the osmotic pressure of the sponges high enough to inhibit metabolism and cell division. Germination could be initiated by the reduction in myo-inositol concentration.
