Effects of cold- and heat hardening on thermal resistance in Drosophila melanogaster

The effects of cold- and heat hardening on resistance to both low and high temperature stress was examined in Drosophila melanogaster lines selected for resistance to either cold or heat. The hardening effect was positive when the hardening was of the same type as the stress in all selection regimes. The effect of cold hardening on survival after heat stress was further examined in the lines selected for cold resistance and corresponding controls. A cross-protection effect (increased heat resistance after cold hardening) was present and this effect was lower in the lines selected for resistance to cold than in the controls. The level of Hsp70 expression induced by a non-lethal cold hardening was examined, showing that cold hardening induced Hsp70 expression. The results suggest that the cross-protection effect is at least partly due to Hsp70 expression induced by cold exposure.     

Effects of exposure to short-term heat stress on fitness components in Drosophila melanogaster

Effects of thermal stress on survival and reproductive success in ten recently collected isofemale lines of Drosophila melanogaster were compared for flies treated as follows: always held at 25° C, placed in an incubator set at 37° C for 120 min, or exposed to 40° C in an incubator for 90 min, with or without previous exposure to 37° C. Short-term exposure to the higher temperature greatly reduced adult survival, the mating frequency of males and females, and female fecundity, which was measured as offspring produced over ten days. Male fertility, measured as the progeny produced by a female mated once, differed little among treatments. Previous exposure to a high, but non-lethal, temperature before exposure to the higher one, improved survival of males and females, and improved offspring production of females. Genetic variation was present among lines for offspring production, but genetic variation for survival was not significant, and genotype by environment interactions for fitness components of females were small. These results indicated low genetic variation in thermal resistance in the studied population, such that a threshold for temperature stress probably exists, above which local extinction is more likely than the evolution of resistance.     

Response of cold-acclimated,farmed South African abalone (Haliotis midae) to short-term and long-term changes in temperature

In its natural environment, the South African abalone, Haliotis midae, occurs at average monthly water temperatures between 12 and 21 °C. In the present study we aimed to describe selected physiological and molecular responses of winter acclimated, cultured H. midae after acute and chronic exposure to 16, 19 and 22 °C.     

Aphid clonal resistance to a parasitoid fails under heat stress

Parasitoid virulence and host resistance are complex interactions depending on metabolic rate and cellular activity, which in aphids additionally implicate heritable secondary symbionts among the Enterobacteriaceae. As performance of the parasitoid, the aphid host and its symbionts may differentially respond to temperature, the success or failure of aphid parasitism is difficult to predict when temperature varies. We tested the hypothesis that resistance of the pea aphid Acyrthosiphon pisum to the parasitoid Aphidius ervi, which is linked to aphid secondary symbionts, may depend on temperature in several resistant and non-resistant aphid clonal lineages of different geographic origin and of known bacterial symbiosis, using experiments in controlled environments. Complete immunity to A. ervi at 20 degrees C in three different aphid clones whose symbiosis is characterized by the possession of Hamiltonella defensa reversed to high susceptibility at 25 degrees C and especially 30 degrees C, suggesting that the aphid's immune responses to the establishment and early development of the parasitoid is strongly reduced at moderately high temperatures. There was no evidence that a pea aphid control genotype that was susceptible to A. ervi at 20 degrees C could become more resistant as temperature increases, as has been suggested for insect fungal pathogens. By contrast, our results suggest that aphid clonal resistance to A. ervi and related parasitoids is characteristic of cool temperature conditions, similar to various other fitness attributes of aphids. Based on evidence that H. defensa symbionts characterized all three A. ervi resistant pea aphid clones studied, but was absent in control aphids that remained susceptible at all temperatures, we suggest that secondary symbiosis plays a key role in the heat sensitivity of aphid clonal resistance. Our study may also indicate that aphid natural control of variably susceptible host populations by aphid parasitoids is more likely at moderate to high temperatures.     

Leishmania amazonensis: effects of heat shock on ecto-ATPase activity

In this work we demonstrated that promastigotes of Leishmania amazonensis exhibit an Mg-dependent ecto-ATPase activity, which is stimulated by heat shock. The Mg-dependent ATPase activity of cells grown at 22 and 28 degrees C was 41.0+/-5.2 nmol Pi/h x 10(7)cells and 184.2+/-21.0 nmol Pi/h x 10(7)cells, respectively. When both promastigotes were pre-incubated at 37 degrees C for 2h, the ATPase activity of cells grown at 22 degrees C was increased to 136.4+/-10.6 nmol Pi/h x 10(7) whereas that the ATPase activity of cells grown at 28 degrees C was not modified by the heat shock (189.8+/-10.3 nmol Pi/h x 10(7)cells). It was observed that Km of the enzyme from cells grown at 22 degrees C (Km=980.2+/-88.6 microM) was the same to the enzyme from cells grown at 28 degrees C (Km=901.4+/-91.9 microM). In addition, DIDS (4,4'-diisothiocyanatostilbene 2,2'-disulfonic acid) and suramin, two inhibitors of ecto-ATPases, also inhibited similarly the ATPase activities from promastigotes grown at 22 and 28 degrees C. We also observed that cells grown at 22 degrees C exhibit the same ecto-phosphatase and ecto 3'- and 5'-nucleotidase activities than cells grown at 28 degrees C. Interestingly, cycloheximide, an inhibitor of protein synthesis, suppressed the heat-shock effect on ecto-ATPase activity of cells grown at 22 degrees C were exposed at 37 degrees C for 2h. A comparison between the stimulation of the Mg-dependent ecto-ATPase activity of virulent and avirulent promastigotes by the heat shock showed that avirulent promastigotes had a higher stimulation than virulent promastigotes after heat stress.     

CHIP interacts with heat shock factor 1 during heat stress

Heat shock factor 1 (HSF1) is a major transactivator of heat shock genes in response to stress and mediates cell protection against various harmful conditions. In this study, we identified the interaction of CHIP (carboxyl terminus of the heat shock cognate protein 70-interacting protein) with the N-terminus of HSF1. Using GST full-down assay, we found that CHIP directly interacts with C-terminal deleted HSF1 (a.a. 1-290) but not with full-length HSF1 under non-stressed conditions. Interestingly, interaction of CHIP with full-length HSF1 was induced by heat shock treatment. The structural change of HSF1 was observed under heat stressed conditions by CD spectra. These observations demonstrate the direct interaction between HSF1 and CHIP and this interaction requires conformational change of HSF1 by heat stress.     

The effect of heat stress on skeletal muscle contractile properties

An elevated heat-shock protein (HSP) content protects cells and tissues, including skeletal muscles, from certain stressors. We determined if heat stress and the elevated HSP content that results is correlated with protection of contractile characteristics of isolated fast and slow skeletal muscles when contracting at elevated temperatures. To elevate muscle HSP content, one hindlimb of Sprague–Dawley rats (21–28 days old, 70–90 g) was subjected to a 15 min 42 °C heat-stress. Twenty-four hours later, both extensor digitorum longus (EDL) and soleus muscles were removed, mounted in either 20 °C or 42 °C Krebs-Ringer solution, and electrically stimulated. Controls consisted of the same muscles from the contra-lateral (non-stressed) hindlimbs as well as muscles from other (unstressed) animals. Isolated muscles were twitched and brought to tetanus every 5 min for 30 min. As expected, HSP content was elevated in muscles from the heat-stressed limbs when compared with controls. Regardless of prior treatment, both EDL and soleus twitch tensions were lower at 42 °C when compared with 20 °C. In addition, when incubated at 42 °C, both muscles showed a drop in twitch tension between 5 and 30 min. For tetanic tension, both muscles also showed an increase in tension between 5 and 30 min when stimulated at 20 °C regardless of treatment but when stimulated at 42 °C no change was observed. No protective effect of an elevated HSP content was observed for either muscle. In conclusion, although heat stress caused an elevation in HSP content, no protective effects were conferred to isolated contracting muscles.     

Heat shock,with recovery,promotes protection of Nicotiana tabacum during subsequent exposure to Ralstonia solanacearum

Host–pathogen interactions in plants are complex and potentially influenced by heat shock/stress (HS). Host HS proteins (HSPs) induced prior to bacterial exposure may facilitate the folding of newly synthesized defense proteins and promote incompatible host–pathogen interactions. We hypothesized that a non-lethal HS, with recovery, promotes protection of Nicotiana tabacum during subsequent exposure to avirulent soilborne necrotrophic pathogen Ralstonia solanacearum. The objective of this study included investigating the effects of HS with or without recovery on the outcome of bacterial exposure to a virulent and avirulent biovar of R. solanacearum in N. tabacum cell suspensions. This was assessed by quantifying host Hsp70/Hsc70 levels, mitochondrial electron (e⁻) transport activity as a marker of viability, and phosphatidylserine externalization and DNA fragmentation as markers of apoptosis. Our findings support the hypothesis that HS, with recovery, promotes protection of N. tabacum during subsequent exposure to R. solanacearum, suggesting a role for Hsp70/Hsc70 in the observed protection of e⁻ transport, increased apoptosis, and DNA fragmentation.     

Protein expression during heat stress in thermo-intolerant and thermo-tolerant diatoms

Diatoms (Chrysophyta) are photosynthetic microorganisms that are abundant in the natural environment and often associated with specific habitat and water quality conditions. Their significance as bioindicators and as exploitable sources of fine chemicals makes them desirable candidates for the study of stress responses. The protein expression of a thermo-intolerant (Phaeodactylum tricornutum) and thermo-tolerant (Chaetoceros muelleri) diatom following exposure to elevated temperature was investigated using one- and two-dimensional gel electrophoresis and Western blot analysis. It was determined using SDS PAGE with ³⁵S-methionine labeled proteins and Western blot analysis using pea HSP70 antisera that higher temperatures and longer duration treatment were required to cause a noticeable stress response in C. muelleri compared to P. tricornutum. This may be explained by C. muelleri possessing higher amounts of constitutively expressed heat shock proteins, which allows these cells to rapidly adjust to temperature increases. Two-dimensional gel electrophoresis revealed that putative small heat shock proteins (smHSPs) may appear to play a role during heat stress in both diatoms, which is similar to the response in plants. SDS PAGE data are also presented characterizing the recovery of P. tricornutum after heat shock. These results suggest that there is a lag period between heat shock and stress protein synthesis in these thermo-intolerant cells. This supports the hypothesis that cells without higher amounts of constitutively expressed stress proteins have a greater sensitivity to increased temperature. Work is underway to identify particular stress proteins responsible for conveying thermo-tolerance and to determine if overexpression of these genes in thermo-intolerant diatoms affects their temperature sensitivity.     

Immunological enhancement action of endotoxin-free tilapia heat shock protein 70 against Streptococcus iniae

The immunological effects of heat shock proteins (HSPs) had been found in humans and mice, but scarce data of endotoxin-free Hsp70 were reported in tilapia. In the current study, we reported that tHsp70 alone and antigen-tHsp70 compound increased the proliferations of lymphocytes and macrophages, significantly increased the NO release and phagocytotic ability of macrophages (p < 0.05), and enhanced the levels of immune-related genes in lymphocytes and macrophages in a dose- and/or time-dependent manner. On the other hand, tHsp70 not only helped to reduce the proliferation inhibitions induced by the ECP treatment, but also assisted antigens to enhance the vaccine-induced protection against Streptococcus iniae (p < 0.05). We described, for the first time, a critical role of endotoxin-free tHsp70 on activation of tilapia lymphocytes and macrophages post S. iniae exposure and its up-regulation effects on vaccine-induced protection. Our research highlights the immunological enhancement action of Hsp70 in teleost immunity.