Low Heat Stress Research Articles

Anatomical Changes of Cultivated Plants under Combined Stress: An Urgent Need for Investigation

The global food production and its quality face a lot of challenges, which already decreased the availability of these foods. These challenges were mainly linked to global climate changes and their ramifications, which are expressed as environmental stresses like drought, flooding, low or high heat stress. The new pandemics like COVID-19 also represent a new challenge for the entire universe. Although, there are increasing concerns about combined stress on cultivated plants, still more studies are needed to cover all botanical issues including physiological, morphological, biochemical and histological traits. Further studies are required to focus on different combined or multiple stresses in particular the individual stress is rare in the nature. This work is an invitation for publication reviews, comments, notes and original articles about the anatomical changes in stressful plants particularly under combined stress. The EBSS journal also welcomes the serious and promising studies, which will handle the environmental issues related to stress in the era of COVID-19.

Ruminal volatile fatty acid absorption is affected by elevated ambient temperature

The objective of this study was to investigate the effect of short-term elevated ambient temperature on ruminal volatile fatty acid (VFA) dynamics and rumen epithelium gene expression associated with the transport and metabolism of VFA. Eight ruminally cannulated Holstein heifers (200 kg) were used in a factorial, repeated measures experiment with two treatments and two periods. During the first period, animals were provided with feed ad libitum and housed at 20 °C. During the second period, one group (HS) was housed at 30 °C and fed ad libitum. The other group (PF) was housed at 20 °C and pair-fed to match the intake of the HS group. During each period, animals were kept on treatment for 10 day, with sample collection on the final day. In the second period, indicators of heat stress were significantly different between PF and HS animals (P < 0.05). There was a thermal environment effect on butyrate production (P < 0.01) that was not associated with feed intake (P = 0.43). Butyrate absorption decreased in HS animals (P < 0.05) but increased in PF animals (P < 0.05) from period 1 to period 2. There was a feed intake effect on BHD1 expression (P = 0.04) and a tendency for a thermal environment effect (P = 0.08), with expression increasing in both cases. Expression of MCT4 was affected by feed intake (P = 0.003) as were all NHE genes (NHE1, NHE2, and NHE3; P < 0.05). These results indicate that with low feed intake and heat stress, there are shifts in rumen VFA dynamics and in the capacity of the rumen epithelium to absorb and transport VFA.

Heat stress reduces growth rate of red deer calf: Climate warming implications.

Climate models agree in predicting scenarios of global warming. In endothermic species heat stress takes place when they are upper their thermal neutral zone. Any physiological or behavioural mechanism to mitigate heat stress is at the cost of diverting energy from other physiological functions, with negative repercussions for individual fitness. Tolerance to heat stress differs between species, age classes and sexes, those with the highest metabolic rates being the most sensitive to stressing thermal environments. This is especially important during the first months of life, when most growth takes place. Red deer (Cervus elaphus) is supposedly well adapted to a wide range of thermal environments, based on its worldwide distribution range, but little is known about the direct effect that heat stress may have on calf growth. We assessed the effect that heat stress, measured by heat stress indices and physical environment variables (air temperature, relative air humidity, wind speed and solar radiation), have on calf and mother body weights from calf´s birth to weaning. We used 9265 longitudinal weekly body weight records of calf and mother across 19 years in captive Iberian red deer. We hypothesised that (i) heat stress in hot environments has a negative effect on calf growth, especially in males, as they are more energetically demanding to produce than females; and that (ii) the body weight of the mother through lactation should be negatively affected by heat stress. Our results supported hypothesis (i) but not so clearly hypothesis (ii). By weaning (day 143) calves growing under low heat stress environment grew up to 1.2 kg heavier than those growing in high heat stress environment, and males were more affected by heat stress than females. The results have implications in animal welfare, geographical clines in body size and adaptation to climate change.

Reliability of Reflex Cutaneous Vasodilation on the Forearm Measured Using Laser‐Doppler Flowmetry During Whole‐body Passive Heating

Laser‐Doppler flowmetry (LDF) quantifies changes in localized microvascular perfusion in response to thermal and non‐thermal stimuli. Despite its widespread use, the reliability of the measurement during whole‐body heating is unknown. This presents a key knowledge gap that is critical for experimental design, statistical analysis, and interpretation. The purpose of this study was therefore to assess the reliability of LDF‐derived cutaneous vasodilation between separate days (between‐day) and between forearm sites (within‐day) during incremental whole‐body heat stress. On three occasions (~1 week apart), 11 healthy men (25 [SD 5] years) were passively heated (whole‐body heating using a water perfused suit) to increase esophageal temperature (Teso) by +0.7°C [0.11] (low heat stress, LHS) and +1.3°C [0.14] (moderate heat stress, MHS). Forearm skin blood flow (arbitrary perfusion units; PU) was measured in three adjacent sites on the mid‐dorsal forearm using LDF (Perimed) while local skin temperature was clamped (34°C). Maximal vasodilation was achieved by heating each skin site to 44°C (for ≥ 20 min), but without the use of SNP, while Teso was clamped at +1.8°C [0.1]. Beat‐to‐beat mean arterial pressure (MAP) was measured continuously. Cutaneous vascular conductance (CVC) at each skin site was calculated as PU/MAP. Data were presented as absolute CVC and percentage of maximal vasodilation (%CVC44). Reliability was assessed at baseline (no heat stress, NHS), LHS, and MHS using the intra‐class correlation coefficient (ICC), with values ≥0.7 considered acceptable for research purposes. Between days, CVC increased from 0.3 [0.2] to 2.0 PU [0.8] at LHS, and then to 2.1 PU [0.8] at MHS. Expressed as %CVC44 this equated to increases from 12 [5] to 68% [15] and then 73% [13]. Within‐day (i.e., between sites), average CVC increased from 0.3 [0.2] to 1.9 PU [0.7] at LHS, and 2.0 PU [0.7] at MHS, which related to an increase from 13 [6] to 71% [15] at LHS, and to 76% [12] at MHS when expressed as %CVC44. At NHS, the between‐ and within‐day reliability of these measurements did not exceed the 0.7 ICC threshold when expressed as CVC or %CVC44 at NHS (range: 0.00 to 0.45). Similarly, at LHS and MHS the between‐day reliability did not exceed 0.7 when expressed as CVC (0.57 and 0.69, respectively) or %CVC44 (both 0.57). While within‐day reliability of %CVC44 at LHS and MHS was not acceptable (0.54 and 0.64, respectively), it was when expressed as CVC (0.74 and 0.71, respectively). We show that the between‐day reliability of this technique was poor, irrespective of the level of whole‐body heat stress, but within‐day reliability was acceptable during heating, but not for resting measurements. This has important implications for studies assessing reactivity of skin vasculature to passive whole‐body hyperthermia, particularly with respect to the expected difference between the signal (i.e., expected change) and noise (i.e., measurement and biological variability), and the need to ensure that repeated measurements reflect the same microvascular environment.Support or Funding InformationNatural Sciences and Engineering Research Council of Canada

Effect of Heat Stress on Measures of Running Performance and Heart Rate Responses During a Competitive Season in Male Soccer Players.

Coker, NA, Wells, AJ, and Gepner, Y. The effect of heat stress on measures of running performance and heart rate responses during a competitive season in male soccer players. J Strength Cond Res 34(4): 1141-1149, 2020-Measures of running performance and heart rate (HR) responses to match play during 3 different heat stress (HS) conditions were assessed in 7 National Collegiate Athletic Association (NCAA) Division I male soccer players. Total distance and distance covered within distinct velocity zones (walking [WALK], jogging [JOG], low-speed running, high-speed running, sprinting [SPRINT], low-intensity running [LIR], and high-intensity running [HIR]) were assessed using global positioning system units for more than 12 matches. Heat stress was monitored during each match, and matches were defined as low (HSlow, n = 4), moderate (HSmod, n = 4), or high (HShigh, n = 4) HS. Minutes played were significantly different across HS conditions (p = 0.03). Therefore, distance covered within each movement velocity was assessed relative to minutes played and as a percentage of total playing time. WALKrel was significantly greater during HShigh compared with HSlow (p = 0.035). LIRrel was significantly greater during HSmod (p = 0.015) compared with HSlow. A trend was observed for %WALK being higher during HShigh compared with HSlow (p = 0.066). %LIR was significantly greater during HShigh compared with HSlow (p = 0.048). High-intensity running was not significantly different across HS conditions. Percent of time spent >85% HRmax was significantly greater during HShigh (p = 0.002) and HSmod (p < 0.001) compared to HSlow. Percent of time spent between 65-84% HRmax was significantly greater during HSlow compared to HShigh (p < 0.001). Results indicate that HS resulted in increased LIR and %HR≥85, while HIR was maintained. High-intensity running performance may be conserved through decreased playing time or the adoption of pacing strategies. This may assist coaches in altering player management strategies to optimize team performance.

Nitrogen pollution interacts with heat stress to increase coral bleaching across the seascape

Climate change is increasing the frequency and magnitude of temperature anomalies that cause coral bleaching, leading to widespread mortality of stony corals that can fundamentally alter reef structure and function. However, bleaching often is spatially variable for a given heat stress event, and drivers of this heterogeneity are not well resolved. While small-scale experiments have shown that excess nitrogen can increase the susceptibility of a coral colony to bleaching, we lack evidence that heterogeneity in nitrogen pollution can shape spatial patterns of coral bleaching across a seascape. Using island-wide surveys of coral bleaching and nitrogen availability within a Bayesian hierarchical modeling framework, we tested the hypothesis that excess nitrogen interacts with temperature anomalies to alter coral bleaching for the two dominant genera of branching corals in Moorea, French Polynesia. For both coral genera, Pocillopora and Acropora, heat stress primarily drove bleaching prevalence (i.e., the proportion of colonies on a reef that bleached). In contrast, the severity of bleaching (i.e., the proportion of an individual colony that bleached) was positively associated with both heat stress and nitrogen availability for both genera. Importantly, nitrogen interacted with heat stress to increase bleaching severity up to twofold when nitrogen was high and heat stress was relatively low. Our finding that excess nitrogen can trigger severe bleaching even under relatively low heat stress implies that mitigating nutrient pollution may enhance the resilience of coral communities in the face of mounting stresses from global climate change.

Water restriction induces behavioral fight but impairs thermoregulation in a dry‐skinned ectotherm

Behavioral fight responses to desiccation risk are important to predict the vulnerability of terrestrial animals to climate change and yet, they have received little attention so far. In terrestrial ectotherms, behavioral regulation of the water balance (i.e. hydroregulation) is likely to be plastic and may tradeoff with thermoregulation behavior because water loss rates are generally higher in warmer environments and body temperatures. When low water availability and heat stress cause physiological dehydration, we expect to highlight a shift to behavioral water‐conservation strategies including changes in activity patterns, micro‐habitat selection and thermoregulation strategies. Here, we compared the behavior of adult common lizards Zootoca vivipara in indoor arenas that either had a permanent access to water or underwent a one‐week long experimental water restriction. Water‐restricted lizards reduced their behavioral activity, selected more often cooler and wetter refuges during daytime, and performed less accurate thermoregulation than control lizards. The activity of water‐restricted gravid females shifted towards the cooler and wetter early hours of the day. In addition, they had lower body temperatures and preferred lower body temperatures at the end of the experiment (i.e. thermal depression). Water‐restricted lizards suffered from a mild physiological dehydration and had a lower mass change. Heat stress was simulated every second day, which led to a range of heat avoidance and water conservation strategies independent from water restriction. Altogether, these results confirm that chronic water restriction and dehydration induce responses towards water conservation that conflict with thermoregulation accuracy.

World Population Variability and Heat Bias Prediction: An Approach to Global Heat Disaster Management

This study examined world population variability and heat bias prediction as an approach to global heat disaster management. Heat bias data were generated from population records of United Nations Department of Economic and Social Affairs, World Population Review and U.S. Census Bureau and International Database using population simulated mathematical model. The world has population of 7,794,798,739 and heat bias of 7.20C and continental mean of 5.40C. Asia had the highest heat bias of 70C, Africa 6.0C, North America 6.40C, Europe 5.70C, South America 5.50C Australia/Oceania 4.80C and the Antarctica had the least heat bias of 2.20C ranging 4.80C. All continents exceeded the recommended +0.5oC-2.5oC human comfort threshold. Countries within the humid tropics had increased heat load. Countries within the subtropics up to the middle latitude had relatively lower heat stress. Population density does not have significant association with heat bias. Heat bias is important in global environmental planning and management.

Chronic kidney disease of unknown etiology (CKDu): Using a system dynamics model to conceptualize the multiple environmental causative pathways of the epidemic

A chronic kidney disease of unknown etiology is devastating agricultural communities of Sri Lanka, Central America, areas of India, and Egypt. Researchers are yet to agree on its etio-pathogenesis despite many cross-sectional, case-control and cohort studies done in these countries. These approaches are broadly based on a reductionist approach. We propose a complementary paradigm based on complexity science to deepen our understanding of the disease. Complexity science views a population as system that has several dynamically interacting and inter-dependent sub-systems and is ‘open’ to the ‘outer’ environment. Health outcomes or epidemics are viewed as ‘emergent’ properties of the population. Using available literature from Sri Lanka, the paper presents a system dynamics model incorporating exposures from pesticides and heavy metals, drinking hard water with high levels of fluoride, poverty, low birth weight, micronutrient deficiencies and heat stress. This approach can be used to model the epidemic, understand the impacts of different factors, predict potential populations at risk, and formulate multi-pronged prevention strategies that target leverage points of the system.

Increasing impacts of extreme droughts on vegetation productivity under climate change

Terrestrial gross primary production (GPP) is the basis of vegetation growth and food production globally1 and plays a critical role in regulating atmospheric CO2 through its impact on ecosystem carbon balance. Even though higher CO2 concentrations in future decades can increase GPP2, low soil water availability, heat stress and disturbances associated with droughts could reduce the benefits of such CO2 fertilization. Here we analysed outputs of 13 Earth system models to show an increasingly stronger impact on GPP by extreme droughts than by mild and moderate droughts over the twenty-first century. Due to a dramatic increase in the frequency of extreme droughts, the magnitude of globally averaged reductions in GPP associated with extreme droughts was projected to be nearly tripled by the last quarter of this century (2075–2099) relative to that of the historical period (1850–1999) under both high and intermediate GHG emission scenarios. By contrast, the magnitude of GPP reductions associated with mild and moderate droughts was not projected to increase substantially. Our analysis indicates a high risk of extreme droughts to the global carbon cycle with atmospheric warming; however, this risk can be potentially mitigated by positive anomalies of GPP associated with favourable environmental conditions. Terrestrial primary productivity will increase with CO2 fertilization, but water limitation will decrease this positive effect. Analyses of Earth system model projections show that extreme droughts will have a much stronger impact on future productivity than mild and moderate droughts.

Envirotypes Based on Seed Yield Limiting Factors Allow to Tackle G × E Interactions

One challenge in plant breeding is to ensure optimized production under fluctuating environments while reducing the environmental impacts of agriculture. Thus, new rapeseed varieties should be adapted to a wide range of pedoclimatic conditions and constraints. Addressing this issue requires identifying the critical factors limiting production and the genotype by environment (G × E) interaction. Our goal was to characterize the effects of environment and G × E interaction on the seed yield of rapeseed grown over a large field network. First, we defined a pedoclimatic indicator set with the ability to highlight the potential limiting factors along the crop cycle by analyzing the yield of two genotypes grown under 20 environments. Out of the 84 pedoclimatic indicators, 10 were identified as limiting after a partial least squares regression analysis. The environments were then clustered into five envirotypes, each characterized by few major limiting factors: low winter temperatures and heat stress during seed filling (1); low solar radiation during seed filling (3); vernalization conditions during winter (4) and high temperatures at flowering (5). A larger genetic diversity was evaluated in a subset of 11 environments to analyze the impact of envirotyping on genotype ranking. Their results were discussed in light of field network management and plant breeding purposes.

Intra-Annual Variability in Responses of a Canopy Forming Kelp to Cumulative Low Tide Heat Stress: Implications for Populations at the Trailing Range Edge.

Anthropogenic climate change is driving the redistribution of species at a global scale. For marine species, populations at trailing edges often live very close to their upper thermal limits and, as such, poleward range contractions are one of the most pervasive effects of ongoing and predicted warming. However, the mechanics of processes driving such contractions are poorly understood. Here, we examined the response of the habitat forming kelp, Laminaria digitata, to realistic terrestrial heatwave simulations akin to those experienced by intertidal populations persisting at the trailing range edge in the northeast Atlantic (SW England). We conducted experiments in both spring and autumn to determine temporal variability in the effects of heatwaves. In spring, heatwave scenarios caused minimal stress to L.digitata but in autumn all scenarios tested resulted in tissue being nonviable by the end of each assay. The effects of heatwave scenarios were only apparent after consecutive exposures, indicating erosion ofresilience over time. Monthly field surveys corroborated experimental evidence as the prevalence of bleaching (an indication of physiological stress and tissue damage) in natural populations was greatest in autumn and early winter. Overall, our data showed that L.digitata populations in SW England persist close to their upper physiological limits for emersion stress in autumn. As the intensity of extreme warming events is likely to increase with anthropogenic climate change, thermal conditions experienced during periods of emersion will soon exceed physiological thresholds and will likely induce widespread mortality and consequent changes at the population level.

Variable interaction outcomes of local disturbance and El Niño-induced heat stress on coral microbiome alpha and beta diversity

Emerging evidence indicates that individual stressors can modify the coral microbiome; however, few studies have examined the impacts of multiple stressors through natural climatic events. During periods of low and high heat stress associated with the 2015–2016 El Nino, we tracked the microbiomes of two coral species (Porites lobata and Montipora aequituberculata) across sites on Kiritimati (Christmas) Island with different levels of local disturbance (i.e. subsistence fishing, pollution, dredging). At low heat stress, local disturbance was associated with increased microbial alpha diversity (i.e. number of microbial OTUs and their relative abundance) in both species and increased beta diversity (i.e. coral to coral variation in microbial community composition) in P. lobata. High levels of thermal stress subsequently elevated microbial beta diversity in both species at the low disturbance sites up to the level experienced at the high disturbance sites under low heat stress, illustrating that each stressor can destabilize the coral microbiome. However, with high heat stress microbial alpha diversity was no longer significantly different between disturbance levels for either species. Survival of P. lobata throughout the entire El Nino event was greater at low disturbance sites than high ones (40% vs. 15%), suggesting that protection from local stressors may enhance survival of stress-tolerant corals. However, no M. aequituberculata tracked in this study survived the thermal anomaly. Whether enhanced survivorship can be directly attributed to lower microbial diversity, however, remains to be tested. Overall, we found that, rather than acting synergistically, multiple stressors either acted antagonistically to one another (alpha diversity for both coral species, beta diversity for P. lobata) or exhibited dominance (beta diversity for M. aequituberculata), suggesting that multiple stressors cause various interaction outcomes on the coral microbiome and highlighting the need for future research to evaluate these interactions and their consequences for coral resilience.

Harnessing anaerobic digestion for combined cooling, heat, and power on dairy farms: An environmental life cycle and techno-economic assessment of added cooling pathways

Anaerobic digestion coupled with combined heat and power production on dairy farms is environmentally advantageous; however, high capital and operating costs have limited its adoption, especially in the United States, where renewable electricity and heat production are under-incentivized. Biogas is also at a disadvantage because it has to compete with very low natural gas prices. The objective of this study was to evaluate the feasibility of integrating absorption refrigeration technology for combined cooling, heat, and power (CCHP) on the farm to help bridge this economic hurdle. A combined environmental life cycle and techno-economic assessment was used to compare 2 cooling pathways with and without co-digestion. We considered using CCHP to (1) displace electricity-driven refrigeration processes (e.g., milk chilling/refrigeration, biogas inlet cooling) or (2) mitigate heat stress in dairy cattle via conductive cow cooling. All cooling scenarios reduced environmental emissions compared with combined heat and power only, with an appreciable reduction in land use impacts when employing conductive cow cooling. However, none of the cooling scenarios achieved economically viability. When using cooling power to displace electricity-driven refrigeration processes, economic viability was constrained by low electricity prices and a lack of incentives in the United States. When used for conductive cow cooling, economic viability was constrained by (1) low waste heat-to-cooling conversion efficiency; (2) limited conductive cow cooling effectiveness (i.e., heat-stress mitigation); and (3) low heat stress frequency and limited severity. However, we predict that with minor improvements in conductive cow cooling effectiveness and in hotter climates, CCHP for conductive cow cooling would be economically viable even in current US energy markets.

Does environmental heat stress impact physical and technical match-play characteristics in football?

ABSTRACTPurpose: To examine the impact of environmental heat stress conditions on physical and technical football match-play characteristics.Method: Data from 42 matches of 9 outfields, professional football players were collected in temperatures ranging from 13°C to 37°C and relative humidity ranging from 11% to 83%. Individual player data were only included if a player had played a full match (>90+ min) and had completed at least one full match in each of the four available environmental heat stress risk conditions of low, moderate, high and excessive.Results: Significant effects were observed for run speed (p = .001), high speed run (p = .041), high intensity (p = .023) and explosive (p = .001) distance covered, with run speed and explosive distance significantly decreasing in excessive compared to low environmental heat stress conditions. Similarly, the number of balls lost (p = .002) significantly decreased in excessive compared to low climatic conditions. Total and sprint distances were unaffected.Conclusion: Excessive environmental conditions may impact physical and to some degree technical match-play characteristics. A rational may be due to professional players employing pacing strategies to modulate their physical exertion in an attempt to control thermal strain and physical fatigue.

The mechanisms underlying the muscle metaboreflex modulation of sweating and cutaneous blood flow in passively heated humans.

Metaboreceptors can modulate cutaneous blood flow and sweating during heat stress but the mechanisms remain unknown. Fourteen participants (31 ± 13 years) performed 1‐min bout of isometric handgrip (IHG) exercise at 60% of their maximal voluntary contraction followed by a 3‐min occlusion (OCC), each separated by 10 min, initially under low (LHS, to activate sweating without changes in core temperature) and high (HHS, whole‐body heating to a core temperature increase of 1.0°C) heat stress conditions. Cutaneous vascular conductance (CVC) and sweat rate were measured continuously at four forearm skin sites perfused with 1) lactated Ringer's solution (Control), 2) 10 mmol L‐NAME [inhibits nitric oxide synthase (NOS)], 3) 10 mmol Ketorolac [inhibits cyclooxygenase (COX)], or 4) 4 mmol theophylline (THEO; inhibits adenosine receptors). Relative to pre‐IHG levels with Control, NOS inhibition attenuated the metaboreceptor‐mediated increase in sweating under LHS and HHS (P ≤ 0.05), albeit the attenuation was greater under LHS (P ≤ 0.05). In addition, a reduction from baseline was observed with THEO under LHS during OCC (P ≤ 0.05), but not HHS (both P > 0.05). In contrast, CVC was lower than Control with L‐NAME during OCC in HHS (P ≤ 0.05), but not LHS (P > 0.05). We show that metaboreceptor activation modulates CVC via the stimulation of NOS and adenosine receptors, whereas NOS, but not COX or adenosine receptors, contributes to sweating at all levels of heating.

263 - Protective Role of Nrf2 during the Adaptive Survival Response Induced by Mild Heat Stress at 40°C

The exposure of cells to low doses of stress induces adaptive survival responses that protect cells against subsequent exposure to toxic stress. The ability of cells to resist subsequent toxic stress following exposure to low dose heat stress at 40°C is known as mild thermotolerance. Thermotolerance is an adaptive survival response that involves increased expression of heat shock proteins and antioxidants. However, the initiating factors in this response are not understood. This study aims to understand the role of the Nrf2 antioxidant pathway in the acquisition of mild thermotolerance at 40°C, and secondly, whether the Nrf2 pathway could be involved in the protective effect of thermotolerance against heat-shock (42°C)-induced apoptosis. During cell preconditioning at 40°C, protein expression of the Nrf2 transcription factor increased. In addition, levels of the Nrf2 targets MnSOD, catalase, heme oxygenase-1, glutamate cysteine ligase and Hsp70 increased at 40°C. Levels of these Nrf2 targets were enhanced by Nrf2 activator oltipraz and decreased by shRNA targeting Nrf2. Moreover, Nrf2 contributes to the protective effect of thermotolerance against heat-shock (42°C)-induced apoptosis: the adaptive response was enhanced by oltipraz, whereas it was partly reversed by Nrf2 knockdown. Improved knowledge about the different protective mechanisms that mild thermotolerance can activate is crucial for the potential use of this adaptive survival response to treat stress-related diseases.

The antioxidant transcription factor Nrf2 contributes to the protective effect of mild thermotolerance (40 °C) against heat shock-induced apoptosis

The exposure of cells to low doses of stress induces adaptive survival responses that protect cells against subsequent exposure to toxic stress. The ability of cells to resist subsequent toxic stress following exposure to low dose heat stress at 40°C is known as mild thermotolerance. Mild thermotolerance involves increased expression of heat shock proteins and antioxidants, but the initiating factors in this response are not understood. This study aims to understand the role of the Nrf2 antioxidant pathway in acquisition of mild thermotolerance at 40°C, and secondly, whether the Nrf2 pathway could be involved in the protective effect of thermotolerance against heat-shock (42°C)-induced apoptosis. During cell preconditioning at 40°C, protein expression of the Nrf2 transcription factor increased after 15–60min. In addition, levels of the Nrf2 targets MnSOD, catalase, heme oxygenase-1, glutamate cysteine ligase and Hsp70 increased at 40°C. Levels of these Nrf2 targets were enhanced by Nrf2 activator oltipraz and decreased by shRNA targeting Nrf2. Levels of pro-oxidants increased after 30–60min at 40°C. Pro-oxidant levels were decreased by oltipraz and increased by knockdown of Nrf2. Increased Nrf2 expression and catalase activity at 40°C were inhibited by the antioxidant PEG-catalase and by p53 inhibitor pifithrin-α. These results suggest that mild thermotolerance (40°C) increases cellular pro-oxidant levels, which in turn activate Nrf2 and its target genes. Moreover, Nrf2 contributes to the protective effect of thermotolerance against heat-shock (42°C)-induced apoptosis, because Nrf2 activation by oltipraz enhanced thermotolerance, whereas Nrf2 knockdown partly reversed thermotolerance. Improved knowledge about the different protective mechanisms that mild thermotolerance can activate is crucial for the potential use of this adaptive survival response to treat stress-related diseases.

The impact of urban planning strategies on heat stress in a climate-change perspective

Spatial and temporal characteristics of outdoor heat stress for a redevelopment area in Gothenburg, Sweden, in a climate change perspective, using mean radiant temperature (Tmrt) as a proxy for heat stress is presented. The impact of climate change on Tmrt was evaluated using statistically downscaled data from a regional climate model. The simulated average Tmrt for the future scenarios was not higher than for today’s climate, because the increased longwave radiation fluxes caused by higher temperatures were offset by reduced shortwave radiation fluxes caused by increased cloudiness. The spatial pattern of Tmrt in the study area during warm and clear weather is primarily governed by the shadow patterns of buildings and vegetation. The highest average-daytime Tmrt was found at open locations, but because open areas also have the highest frequency of sunlit occasions, this does not necessarily imply that open areas are most prone to heat-stress. When considering only occasions during clear and warm weather situations, the highest Tmrt were usually found close to sun-exposed, south-facing walls. Under these criteria, denser urban environments have lower heat stress than more open urban environments. The warmest areas were also found to be the warmest areas in the future as well.Tree-shadows are an effective measure to reduce daytime Tmrt. Trees was found to have the largest impact on Tmrt in open areas where vegetation is sparse, especially when the distance to the nearest “cool” place is used as a measure of heat-stress.

Determination of critical heat transfer for the prediction of materials damages during a flame engulfment test

SummaryThe personal protective equipment of workers exposed to heat can consist of materials with a relatively low melting point of approximately 250°C (membranes, zippers, and underwear). In particular, users of heat protective clothing (such as volunteer firefighters or industrial workers) are often consider using functional sports underwear for an optimized sweat transport and lower heat stress. However, in an emergency situation (flame engulfment), this kind of clothing can be potentially dangerous because of its low melting temperature. In this study, we investigated the critical heat transfer needed to melt synthetic underwear worn under heat protective clothing and developed a model to predict possible damage to material layers exposed to a flame engulfment condition. The fire protection properties of four clothing systems with varying layer structures were assessed. These combinations were tested on an instrumented manikin according to ISO 13506 (flame engulfment test). The thickness and thermal resistance of the individual garments were measured in order to examine the influence of each parameter on the performance of the complete clothing combination. The measurements showed that synthetic polyester underwear worn underneath heat protective clothing can withstand a 4s flame engulfment exposure without damage when the outer layer has an adequate thermal resistance. By using a simple heat transfer model, we could define a ‘critical thermal resistance’ as the thermal resistance of the outer layer required to prevent the melting of the underwear material. Copyright © 2016 John Wiley &amp; Sons, Ltd.