Stress-induced accumulation of glycerol in the flesh fly, Sarcophaga bullata: Evidence indicating anti-desiccant and cryoprotectant functions of this polyol and a role for the brain in coordinating the response

Department of Biology, Wittenberg University, Springfield, OH 45501, USA.
Journal of Insect Physiology (Impact Factor: 2.47). 03/2006; 52(2):202-14. DOI: 10.1016/j.jinsphys.2005.10.005
Source: PubMed


Nondiapausing larvae of the flesh fly, Sarcophaga bullata, responded to several forms of short-term environmental stress (low temperature, anoxia and desiccation) by accumulating glycerol. Elevation of this polyol, regardless of the type of stress that induced accumulation, conferred cold resistance: larvae with high glycerol levels were 3-4 times more tolerant of a 2h exposure to -10 degrees C than unstressed larvae. Protection against low temperature injury, as well as dehydration, was also attained by injection of exogenous glycerol into third instar larvae. This artificially induced cold hardiness was only temporary: when glycerol-injected larvae were exposed to -10 degrees C immediately after injection, survival was high, but none survived if they were injected and then held at 25 degrees C for 2 days before the -10 degrees C exposure. Larvae ligated behind the brain immediately after low temperature exposure failed to accumulate glycerol, but glycerol did accumulate in larvae ligated 6-24h after cold treatment, thus implying a critical role for the brain in initiating glycerol production. Interestingly, a much shorter exposure (2h) to low temperature was sufficient to reduce the maximum rate of water loss. Collectively, these observations suggest that multiple pathways may be exploited in response to stress: one pathway is most likely associated with rapid cold hardening (RCH) which generates immediate protection, and a second pathway remains activated for a longer period to enhance the initial protection afforded by glycerol.

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    • "Thus, suppressed respiration and a greater abundance of cuticular lipids, along with increased body size, probably account for most of the observed reduction in rates of water loss. Other factors that could potentially contribute to the reduced water loss rates may be increased levels of polyols, such as glycerol (Yoder et al., 2006), increased melanization (Parkash et al., 2009, 2014), changes in the thickness of the cuticle (Reidenbach et al., 2014) and reduced expression/activity of aquaporins (Liu et al., 2011; Benoit et al., 2014), all of which have been documented to suppress insect water loss rates. Corn earworm pupae are unable to maintain water mass at relative humidities below saturation, indicating that this developmental stage of H. zea is unable to replace lost water by absorbing it from the air. "
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    ABSTRACT: One critical aspect of an insect's ability to overwinter successfully is the effective management of its water resources. Maintenance of adequate water levels during winter is challenging because of the prevailing low relative humidity at that time of year and the short supply of environmental water that is not in the form of ice. These issues are further exacerbated for insects overwintering as pupae, comprising an immobile stage that is unable to move to new microhabitats if conditions deteriorate. The present study compares the water balance attributes of diapausing and nondiapausing pupae of the corn earworm Helicoverpa zea Boddie, aiming to identify the mechanisms used by diapausing pupae to maintain water balance during winter. Diapausing pupae are 10% larger than nondiapausing individuals. Water loss rates for nondiapausing pupae are low (0.21 mg h−1) and are suppressed (0.01 mg h−1) in diapausing pupae. Cuticular lipids, which serve to waterproof the cuticle and thus suppress cuticular water loss, are more than two-fold more abundant on the surface of diapausing pupae, and oxygen consumption rates during diapause drop to almost one-third the rate observed in nondiapausing pupae. Water gain can be accomplished only when atmospheric water content is near saturation or during contact with free water. At moderate relative humidities (20–40%), water loss rates are very low for diapausing pupae, suggesting that these moth pupae have robust mechanisms for combating water loss. The exceptional ability of H. zea to suppress water loss during diapause is probably a result of the combined effects of increased size, more abundant cuticular lipids and decreased metabolic rates.
    Physiological Entomology 10/2015; DOI:10.1111/phen.12119 · 1.42 Impact Factor
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    • "Although the alterations in these sugars are small, they may have beneficial effects on membrane function (Overgaard et al., 2014). Moreover, Yoder et al. (2006) demonstrated that an increase in the glycerol levels significantly improved chill tolerance, as may also happen for G. coquereliana. Together, our results demonstrate that the tropical cockroach G. coquereliana responds to cold stress by a shift in biochemical pathways , which results in the synthesis of compounds that protect the insect from or desensitize it to temperature changes. "
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    ABSTRACT: Insects cope with thermal stressors using mechanisms such as rapid cold hardening and acclimation. These mechanisms have been studied in temperate insects, but little is known about their use by tropical insects in response to cold stress. Here, we investigated whether cold stress (1 × 8 h and 3 × 8 h at 4 °C) triggers a metabolic response in the Madagascar cockroach Gromphadorhina coquereliana. We examined the effects of cold on the levels of selected metabolites in the fat body tissue of G. coquereliana. After cold exposure, we found that the quantity of total protein increased significantly in the insect fat body, whereas glycogen decreased slightly. Using antibodies, we observed upregulation of AQP-like proteins and changes in the HSP70 levels in the fat body of G. coquereliana when exposed to cold. We also examined the content and nature of the free sugars in the G. coquereliana hemolymph and discovered an increase in the levels of polyols and glucose in response to cold stress. These results suggest an important role of the fat body tissue of tropical insects upon cold exposure.
    Comparative Biochemistry and Physiology - Part A Molecular & Integrative Physiology 01/2015; 183. DOI:10.1016/j.cbpa.2015.01.007 · 1.97 Impact Factor
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    • "Glycerol and sorbitol, as the most common cryoprotectant molecules, lower the supercooling points and protect against protein denaturation 69. Glycerol kinase (CL3214.Contig1) is a rate-limiting enzyme in glycerol utilization 70, increasingly expressed during diapause to promote glycerol biosynthesis which was stress-induced and related to high cold resistance (Figure 8) 71. In a specific way, sorbitol dehydrogenase (CL3305.Contig1), related to diapause termination in eggs of B. mori 72, was upregulated in LD (Figure 8). "
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    ABSTRACT: Bactrocera minax is a major citrus pest distributed in China, Bhutan and India. The long pupal diapause duration of this fly is a major bottleneck for artificial rearing and underlying mechanisms remain unknown. Genetic information on B. minax transcriptome and gene expression profiles are needed to understand its pupal diapause. High-throughput RNA-seq technology was used to characterize the B. minax transcriptome and to identify differentially expressed genes during pupal diapause development. A total number of 52,519,948 reads were generated and assembled into 47,217 unigenes. 26,843 unigenes matched to proteins in the NCBI database using the BLAST search. Four digital gene expression (DGE) libraries were constructed for pupae at early diapause, late diapause, post-diapause and diapause terminated developmental status. 4,355 unigenes showing the differences expressed across four libraries revealed major shifts in cellular functions of cell proliferation, protein processing and export, metabolism and stress response in pupal diapause. When diapause was terminated by 20-hydroxyecdysone (20E), many genes involved in ribosome and metabolism were differentially expressed which may mediate diapause transition. The gene sets involved in protein and energy metabolisms varied throughout early-, late- and post-diapause. A total of 15 genes were selected to verify the DGE results through quantitative real-time PCR (qRT-PCR); qRT-PCR expression levels strongly correlated with the DGE data. The results provided the extensive sequence resources available for B. minax and increased our knowledge on its pupal diapause development and they shed new light on the possible mechanisms involved in pupal diapause in this species.
    International journal of biological sciences 09/2014; 10(9):1051-63. DOI:10.7150/ijbs.9438 · 4.51 Impact Factor
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