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Temperature, humidity and inoculative freezing are all signals for glucose accumulation in the freeze tolerant earthworm Dendrobaena octaedra
Abstracts / Comparative Biochemistry and Physiology, Part A 146 (2007) S149–S157
organisms into reversible dormant stages or survival during desiccating conditions. Genomic, proteomic and metabolomic tools used in the course of our studies aim at identifying the molecular and cellular processes that enable five model organisms to tolerate adverse conditions. These are: Cyanobacteria that have specialized dormant cells (akinetes) that tolerate unfavourable environmental conditions. Baker's yeast that can survive long periods in a spore phase, that are characterized by desiccation and high levels of trehalose. Rotifers that produce eggs (resting eggs) containing developmental-arrested embryos after sexual (but not asexual) reproduction. Arctic springtails that reduce their body water content to avoid freezing while producing trehalose and becoming metabolically inactive. Killifish embryos in eggs that show resistance to environmental desiccation conditions. Our studies aim at revealing the mechanisms that establish dormancy and resistance to desiccation, those that allow the revival from dormant stages and the properties that make dormant stages stress-tolerant. The search for common denominators will assist in leading potentially useful strategies for artificial induction of dormancy and of cell preservation. doi:10.1016/j.cbpa.2007.01.316
A9.18 Slow dehydration increases desiccation tolerance in Dendrobaena octaedra cocoons C. Ryge Petersen, J. Overgaard, M. Holmstrup, (DMU) Effect of drought on survival and water content (WC) was investigated in egg capsules (cocoons) of the earthworm Dendrobaena octaedra. Cocoons were harvested from cultured earthworms and allowed to develop to a known intermediary developmental stage. WC and survival was measured during acute or gradually increasing (10 days) exposure to three different levels of desiccation stress at 20 °C (93%, 91% or 89% RH). The WC following the acute treatment was significantly lower (0.40, 0.34 and 0.24 mg water mg dw−1 at 93%, 91% and 89% RH, respectively) than when exposed to gradually increasing desiccation (WC = 0.46, 0.44 and 0.39 mg water mg dw−1, respectively). These results indicate that cocoons accumulate larger concentrations of osmolytes during gradual treatment. Survival was also higher for the gradually dehydrated cocoons. These results were confirmed in a second experiment. Cocoons pre-treated with a gradual exposure to a RH of 91% were compared to untreated cocoons following exposure to a series of harsh desiccation treatments (from 91% to 78% RH for 4 days). Both WC and survival were higher in the pre-acclimated (gradually desiccated) cocoons.
S155
Survival in the gradually desiccated cocoons was also higher if the two treatment groups were compared at the same level of dehydration (i.e. WC being the same). This suggests that the difference is not only due to a colligative effect of osmolytes but also due to induction of other protective mechanisms. We are currently examining if and how acutely and gradually exposed cocoons differ in their accumulation of sugars and stress proteins (LEA). doi:10.1016/j.cbpa.2007.01.317
A9.19 Temperature, humidity and inoculative freezing are all signals for glucose accumulation in the freeze tolerant earthworm Dendrobaena octaedra J. Overgaard, M. Holmstrup, (National Environmental Research Institute); M. Bayley, (Aarhus University) Dendrobaena octaedra (the moss worm) is known for its ability to tolerate freezing of its extracellular body fluids. Unlike most temperate earthworm species D. octaedra does not seek refuge in deeper and warmer soils during winter, but instead it remains in the top soil layers where it risks freezing. Like in many freezetolerant amphibians, the freezing event is linked to a quick formation of glucose from the rapid breakdown of glycogen. In some individuals this glucose accumulation can account for more than 15% of dry body mass. Previous studies have shown that both inoculative freezing and rapid osmotic stress can induce glucose accumulation. Consequently it has been thought that D. octaedra accumulates cryoprotectants as a response to the osmotic stress associated with freezing of the extracellular water. In the present study we show that extracellular freezing is not the only cue that triggers glucose accumulation in D. octaedra. Thus, glucose increased more than 10-fold when temperature was lowered + 1 to − 1 °C. This increase occurred independent of extracellular freezing and all worms were unfrozen and active at −1 °C regardless if the soil was frozen or not. The water vapour pressure of ice is lower than that of super cooled water at any given temperature. The relative humidity (RH) in frozen soil is therefore lower than in unfrozen soil. To test whether glucose accumulation could be initiated by a small difference in RH, we exposed worms to mild desiccation stress at +1 °C, equivalent to the dehydration stress of exposure to frozen soil at − 1 °C. We found that this treatment elicited glucose accumulation in ∼ 30% of the individuals and our finding suggest that accumulation of cryoprotectants can be initiated by several separate mechanisms in D. octaedra. These results indicate that these earthworms register small changes in temperature and humidity and their sensibility to these changes may enable them to respond quicker with regard to cryoprotectant accumulation. doi:10.1016/j.cbpa.2007.01.318
organisms into reversible dormant stages or survival during desiccating conditions. Genomic, proteomic and metabolomic tools used in the course of our studies aim at identifying the molecular and cellular processes that enable five model organisms to tolerate adverse conditions. These are: Cyanobacteria that have specialized dormant cells (akinetes) that tolerate unfavourable environmental conditions. Baker's yeast that can survive long periods in a spore phase, that are characterized by desiccation and high levels of trehalose. Rotifers that produce eggs (resting eggs) containing developmental-arrested embryos after sexual (but not asexual) reproduction. Arctic springtails that reduce their body water content to avoid freezing while producing trehalose and becoming metabolically inactive. Killifish embryos in eggs that show resistance to environmental desiccation conditions. Our studies aim at revealing the mechanisms that establish dormancy and resistance to desiccation, those that allow the revival from dormant stages and the properties that make dormant stages stress-tolerant. The search for common denominators will assist in leading potentially useful strategies for artificial induction of dormancy and of cell preservation. doi:10.1016/j.cbpa.2007.01.316
A9.18 Slow dehydration increases desiccation tolerance in Dendrobaena octaedra cocoons C. Ryge Petersen, J. Overgaard, M. Holmstrup, (DMU) Effect of drought on survival and water content (WC) was investigated in egg capsules (cocoons) of the earthworm Dendrobaena octaedra. Cocoons were harvested from cultured earthworms and allowed to develop to a known intermediary developmental stage. WC and survival was measured during acute or gradually increasing (10 days) exposure to three different levels of desiccation stress at 20 °C (93%, 91% or 89% RH). The WC following the acute treatment was significantly lower (0.40, 0.34 and 0.24 mg water mg dw−1 at 93%, 91% and 89% RH, respectively) than when exposed to gradually increasing desiccation (WC = 0.46, 0.44 and 0.39 mg water mg dw−1, respectively). These results indicate that cocoons accumulate larger concentrations of osmolytes during gradual treatment. Survival was also higher for the gradually dehydrated cocoons. These results were confirmed in a second experiment. Cocoons pre-treated with a gradual exposure to a RH of 91% were compared to untreated cocoons following exposure to a series of harsh desiccation treatments (from 91% to 78% RH for 4 days). Both WC and survival were higher in the pre-acclimated (gradually desiccated) cocoons.
S155
Survival in the gradually desiccated cocoons was also higher if the two treatment groups were compared at the same level of dehydration (i.e. WC being the same). This suggests that the difference is not only due to a colligative effect of osmolytes but also due to induction of other protective mechanisms. We are currently examining if and how acutely and gradually exposed cocoons differ in their accumulation of sugars and stress proteins (LEA). doi:10.1016/j.cbpa.2007.01.317
A9.19 Temperature, humidity and inoculative freezing are all signals for glucose accumulation in the freeze tolerant earthworm Dendrobaena octaedra J. Overgaard, M. Holmstrup, (National Environmental Research Institute); M. Bayley, (Aarhus University) Dendrobaena octaedra (the moss worm) is known for its ability to tolerate freezing of its extracellular body fluids. Unlike most temperate earthworm species D. octaedra does not seek refuge in deeper and warmer soils during winter, but instead it remains in the top soil layers where it risks freezing. Like in many freezetolerant amphibians, the freezing event is linked to a quick formation of glucose from the rapid breakdown of glycogen. In some individuals this glucose accumulation can account for more than 15% of dry body mass. Previous studies have shown that both inoculative freezing and rapid osmotic stress can induce glucose accumulation. Consequently it has been thought that D. octaedra accumulates cryoprotectants as a response to the osmotic stress associated with freezing of the extracellular water. In the present study we show that extracellular freezing is not the only cue that triggers glucose accumulation in D. octaedra. Thus, glucose increased more than 10-fold when temperature was lowered + 1 to − 1 °C. This increase occurred independent of extracellular freezing and all worms were unfrozen and active at −1 °C regardless if the soil was frozen or not. The water vapour pressure of ice is lower than that of super cooled water at any given temperature. The relative humidity (RH) in frozen soil is therefore lower than in unfrozen soil. To test whether glucose accumulation could be initiated by a small difference in RH, we exposed worms to mild desiccation stress at +1 °C, equivalent to the dehydration stress of exposure to frozen soil at − 1 °C. We found that this treatment elicited glucose accumulation in ∼ 30% of the individuals and our finding suggest that accumulation of cryoprotectants can be initiated by several separate mechanisms in D. octaedra. These results indicate that these earthworms register small changes in temperature and humidity and their sensibility to these changes may enable them to respond quicker with regard to cryoprotectant accumulation. doi:10.1016/j.cbpa.2007.01.318