Determining factors for cryoprotectant accumulation in the freeze‐tolerant earthworm, Dendrobaena octaedra

Abstract

The freeze-tolerant earthworm Dendrobaena octaedra is found in most of the European forest and tundra, Siberia, North America and Greenland where it over-winters in the top soil and encounters winter frost. In response to freezing this earthworm rapidly synthesises glucose which acts as a cryoprotectant. Frost tolerance varies extensively between geographical populations, and of the populations studied so far, the Finnish worms are most and the Danish worms least frost tolerant. Little is known about the determining factors for glucose synthesis and this study therefore investigated possible roles of acclimation and the cues for synthesis of glucose, in Finnish and Danish worms. The Finnish population had significantly larger glycogen reserves than the Danish during acclimation and in all worms, glucose synthesis was the result of an almost stoichemical reduction in glycogen stores. Maximum glucose levels were reached after the onset of freezing and were significantly higher in Finnish worms where the sugar accounted for as much as 5% of the fresh weight. On average, both the total glycogen phosphorylase activity and the active enzyme pool increased during acclimation in the Finnish but not the Danish populations. However, the increase in this enzyme was only significant during the freezing process. In this study, we show contrary to previous theory that glucose synthesis is initiated before the onset of freezing and that in this species, cryoprotectant synthesis is sensitive to very small temperature changes below 0 degrees C without the presence of ice.

Dual roles of glucose in the freeze-tolerant earthwormDendrobaena octaedra: cryoprotection and fuel for metabolism

“…Moreover, several studies have found large individual differences in glucose accumulation that do not necessarily relate to freezing survival of individuals. Thus, individuals that accumulate relatively low amounts of glucose may also survive short-term freeze-tolerance tests (Rasmussen and Holmstrup, 2002;Overgaard et al, 2007). A similar relationship is also seen when considering interspecific differences since some species of earthworms, such as Aporrectodea caliginosa, show some freeze tolerance although their cryoprotectant accumulation response is limited .…”

“…Glucose is the only cryoprotectant that accumulates in response to freezing in D. octaedra (Bundy et al, 2003;Rasmussen and Holmstrup, 2002;Holmstrup, 2003) and similarly glucose has also been found to be the most predominant cryoprotectant in many freeze-tolerant amphibians (Schmid, 1982;Storey and Storey, 1992;Storey and Storey, 1996). In D. octaedra it seems that the rapid accumulation of glucose is triggered by small temperature changes below 0°C but accumulation is also induced by rapid changes in osmotic pressure such as those following extracellular ice formation (Rasmussen and Holmstrup, 2002;Holmstrup, 2003;Overgaard et al, 2007).…”

Soil salinity increases survival of freezing in the enchytraeidEnchytraeus albidus

“…Glycogen is the principal source for mobilization of carbohydrate cryoprotectants in terrestrial oligochaetes Overgaard et al, 2007), and glucose acts as their main cryoprotectant, probably because it is the primary blood sugar of these animals (Prentø, 1987).…”

Slow desiccation improves dehydration tolerance and accumulation of compatible osmolytes in earthworm cocoons (Dendrobaena octaedraSavigny)

“…The accumulation of glucose in high concentrations is known in post-embryonic stages of D. octaedra subjected to freezing, desiccation or osmotic shock (Overgaard et al, 2007;Rasmussen and Holmstrup, 2002), and thus the occurrence of this carbohydrate was to be expected in dehydrated embryos. However, mannitol, trehalose, alanine and perhaps most interesting, betaine, were also found.…”