The critical thermal limits for the stone loach, Noemacheilus barbatulus, from three populations in north-west England

1. The chief objective was to determine the upper and lower thermal limits for feeding and survival in the stone loach, Noemacheilus barbatulus, using juveniles (total length 30–45 mm, live weight 0.25–0.80 g) from one population and adults (total length 77–100 mm, live weight 3.6–7.9 g) from three populations. 2. Fish were acclimatized to constant temperatures of 3, 7, 10, 15, 20, 25 and 27°C; then the temperature was changed at a rate of 1°C/30min to determine the critical limits for feeding, survival over 7 days (incipient lethal temperature), or survival for 10 min or less (ultimate lethal temperature). The rate of 1°C/30min was the optimum value from preliminary experiments, using nine rates from 0.5°C/48h to 18°Ch^?1. As values for adults were not significantly different between populations, they were pooled to provide arithmetic means (with 95% CL) for the thermal limits at each acclimation temperature. 3. Feeding limits increased with acclimation temperature to upper and lower mean values of 28.0 ± 0.15°C and 5.1 ± 0.55°C for adults, 25.0 ± 0.54°C and 6.1 ± 0.92°C for juveniles. Incipient lethal levels defined a tolerance zone within which stone loach survive for a considerable time; upper limits increased with acclimation temperature to reach a maximum plateau of 29.1 ± 0.18°C for adults and 29.0 ± 0.40°C for juveniles; lower limits also increased from near 0°C to 3.0 ± 0.40°C for adults and juveniles. Upper limits for the ultimate lethal level increased with acclimation temperature to a maximum plateau of 33.5°C for adults (95% CL ± 0.19) and juveniles (95% CL ± 0.40), whilst the lower limits increased from near 0°C to 2.5 ± 0.30°C. At acclimation temperatures below 20°C, upper incipient and ultimate lethal values were significantly lower for juveniles than those for adults. 4. The thermal tolerance of stone loach was higher than that of juvenile Atlantic salmon or brown trout, one or both of these species often being dominant in streams with stone loach.     

The critical thermal limits for the bullhead, Cottus gobio, from three populations in north-west England

1. The objective was to determine the thermal limits for feeding and survival in the bullhead, Cottus gobio, using juveniles (total length 20–30 mm, live weight 0.5–1.5 g) from one population and adults (50–70 mm, 3.5–5.5 g) from three populations. 2. Fish were acclimated to constant temperatures (3, 7, 10, 15, 20, 25 or 27 °C) and the temperature was then changed at a rate of 1 °C /30 min to determine the critical limits for feeding, survival over 7 days (incipient lethal temperature), or survival for 10 min or less (ultimate lethal temperature). The rate of 1 °C/30 min was the optimum value from preliminary experiments, using nine rates from 0.5 °C/48 h to 18 °C h^?1. As values for adults were not significantly different between populations, they were pooled to provide arithmetic means (with 95% CL) for the thermal limits at each acclimation temperature. 3. Feeding limits increased with acclimation temperature to upper and lower mean values (± 95% CL) of 26.5 ± 0.16 °C and 4.2 ± 0.20 °C for adults, 26.6 ± 0.59 °C and 5.0 ± 0.55 °C for juveniles. Incipient lethal levels defined a tolerance zone within which fish survive indefinitely; upper limits increased with acclimation temperature to a plateau of 27.6 ± 0.22 °C for adults and 27.5 ± 0.47 °C for juveniles, lower limits increased from near 0 °C to 2.5 ± 0.31 °C for adults and 2.7 ± 0.47 °C for juveniles. Ultimate lethal levels increased with acclimation temperature to a plateau of 32.5 ± 0.24 °C for adults and 32.6 ± 0.46 °C for juveniles, whilst the lower limits increased from near 0 to 0.9 ± 0.29 °C. Upper feeding, incipient and ultimate lethal values were significantly lower for juveniles than those for adults at acclimation temperatures < 20, < 20 and < 15 °C, respectively. 4. The thermal tolerance of bullheads was slightly lower than that of stone loach, similar to that of juvenile Atlantic salmon and higher than that of brown trout; the thermal limits for feeding were much wider than those for salmon or trout.     

Effects of daily and intermittent exposures on heat acclimation of women

Twelve women, who differed in physical condition and body size, were heat acclimated utilizing either a daily or intermittent (every 3rd day) exposure pattern in an environmental chamber. The women walked for 100 min at 5.2 km/h up a 2.5% grade on a motor-driven treadmill Climatic chamber conditions were 46.5°C T_a, 24.5°C T_wb ± 0.5°C. Although individual acclimation varied, significant reduction in heat strain was observed in all subjects, e.g., the ability to complete the assigned task with increasing ease, a decrease in working heart rate, a decrease in rectal temperature rise, a decrease in mean skin temperature, an increase in sweat rate, an increase in evaporative rate, and a decrease in heat storage. The pattern of heat exposures, daily or every third day, had no discernible effect on the rate of heat acclimation. The highly conditioned subjects showed less physiological strain, particularly during the first few heat exposures, and maintained some relative advantage throughout the series of 10 exposures. Body size, in the range studied, appeared to exert little influence on the amount of thermal strain.     

Effect of heat stress on development in vitro and in vivo and on synthesis of heat shock proteins in porcine embryos

The present study was conducted (1) to examine the effect of an acute increase in ambient temperature on the development of porcine day 6 embryos in culture and after transfer to recipient gilts, and (2) to analyze intracellular production of heat shock proteins (hsps). The viability of porcine day 6 embryos following a temporary acute elevation in ambient temperature (at 42°–45.5°C and for 10–180 min) was examined. Synthesis of 70 kDa hsp (hsp 70) and 90 kDa hsp (hsp90) was determined by SDS-PAGE and Western blot analysis in porcine day 6 embryos subjected to heat stresses. Nonheat-stressed embryos were considered as control. Significantly higher numbers of viable nuclei were observed in treatment groups of 42°C-10 min (236.6 ± 71.4; P < 0.05) and 43°C-30 min (276.8 ± 89.4; P < 0.005) compared to control (173.9 ± 53.9). The 42°C-180 min group (158.0 ± 27.1 μm) had a greater increase in diameter after 24 hr in culture following heat stress compared to control (82.5 ± 47.3 μm), while heat stress with 43°C for ≧60 min, 44°–44.5°C for ≧30 min, or 45°-45.5°C for ≧10 min impaired their survival, as assessed by differences in number of viable nuclei. The embryos subjected to heat stresses under the conditions of 42°C-180 min, 43°C-10 min, 43°C-30 min, 44°C-10 min, or 45°C-10 min developed to normal piglets after transfer to recipient gilts. Overall pregnancy rate was 75% (6/8), and farrowing rate 62.5% (5/8). Of heat-stressed embryos transferred, 59% (36/61) developed to normal piglets. Heat-stress conditions of 42°C for 180 min, 43°C for 30 min, 44°C for 10 min, and 45°C for 10 min were determined as critical with respect to the in vitro and in vivo survival of porcine embryos. Porcine day 6 embryos constitutively synthesized hsp70 even without heat stress, while hsp90 was detected only at trace level. Neither hsp70 nor hsp90 levels increased in the embryos subjected to heat stresses. In conclusion, porcine day 6 embryos could continue to develop in vivo or during in vitro culture after exposure to acute and temporary rise in temperature. However, no increase of hsp70 and hsp90 was observed in the heat-stressed porcine embryos, while hsp70 was detected in the nonheat-stressed porcine embryos. The precise mechanism of the thermotolerance was unclear. © 1996 Wiley-Liss, Inc.     

Temperature dependence-independence of antifreeze turnover in Eurosta solidaginis (Fitch)

Temperature effects on antifreeze metabolism were investigated in two populations (northern and southern) of the golden rod gallfly, Eurosta solidaginis. Sorbitol production was temperature dependent and was triggered by short-term exposure to < +10°C. The maximal rate sorbitol synthesis occurred at 0°C. For both populations, sorbitol was rapidly catabolized during warm acclimation at +20°C. During the first 12 h of warm acclimation, sorbitol levels decreased by 36% (19.7 ± 0.6) to 12.6 ± 1.2 μg/mg) and by 83% (to 3.3 ± 1.7 μg/mg) after 48 h in the northern population. The southern population decreased sorbitol levels 64% (11.8 ± 0.69 to 4.2 ± 0.62) after 48 h. The southern population resynthesized more sorbitol than did the northern population upon re-exposure to 0°C. Glycerol levels increased linearly during the experimental period independent of temperature.     

Tolerance and resistance to thermal stress in juvenile Atlantic salmon, Salmo salar

SUMMARY. 1. The chief objective was to construct a thermal tolerance polygon for juvenile Atlantic salmon, Salmo salar L., using fish from four groups and two populations: two age groups from one population (0+, 1+ parr from River Leven), two size groups from the other population (slow and Fast growing 1+ parr from River Lune). 2. Fish were acclimated to constant temperatures of 5, 10, 15, 20, 25 and 27°C; then the temperature was raised or lowered at 1°C h^?1 to determine the upper and lower limits for feeding and survival over 10 min, 100 min, 1000 min and 7 days. As they were not significantly different between the four groups of fish, values at each acclimation temperature were pooled to provide arithmetic means (with SE) for the thermal tolerance polygon. 3. Incipient lethal levels (survival over 7 days) defined a tolerance zone within which salmon lived for a considerable time; upper mean incipient values increased with increasing acclimation temperature to reach a maximum of 27.8±0.2°C, lower mean incipient values were below 0°C and were therefore undetermined at acclimation temperatures <20°C but increased at higher acclimation temperatures to 2.2±0.4°C. Resistance to thermal stress outside the tolerance zone was a function of time; the ultimate lethal level (survival for 10 min) increased with acclimation temperature to a maximum of 33°C whilst the minimum value remained close to 0°C. Temperature limits for feeding increased slightly with acclimation temperature to upper and lower mean values of 22.5±0.3°C and 7.0±0.3°C. 4. In spite of different methodologies, values in the present investigation are similar to those obtained in previous, less comprehensive studies in the laboratory. They also agree with field observations on the temperature limits for feeding and survival. Thermal tolerance polygons are now available for eight species of salmonids and show that the highest temperature limits for feeding and survival are those recorded for juvenile Atlantic salmon.     

No effects of acclimation to heat on immune and hormonal responses to passive heating in healthy volunteers

Heat acclimation results in whole body-adaptations that increase heat tolerance, and might also result in changed immune responses. We hypothesized that, after heat acclimation, tumor necrosis factor alpha, interleukin 6 and the lymphocyte count would be altered. Heat acclimation was induced in 6 healthy men by 100 min of heat exposure for 9 days. Heat exposure consisted of (1) 10 min of immersion up to chest-level in water at 42°C and (2) 90 min of passive heating by a warm blanket to maintain tympanic temperature at 37.5°C. The climatic chamber was maintained at 40°C and a relative humidity of 50%. Blood samples were analyzed before and after heat acclimation for natural killer (NK) cell activity, counts of lymphocytes B and T, before and after heat acclimation for peripheral blood morphology, interleukin 6, tumor necrosis factor alpha, and cortisol. A Japanese version of the profile of mood states questionnaire was also administered before and after acclimation. The concentrations of white blood cells, lymphocytes B and T, cortisol, interleukin 6, tumor necrosis factor alpha and NK cell activity showed no significant differences between pre- and post-acclimation, but there was a significantly lower platelet count after acclimation and, with the profile of mood states questionnaire, there was a significant rise in anger after acclimation. It is concluded that heat acclimation by passive heating does not induce alterations in immune or endocrine responses.     

Effect of photoperiod and cold acclimation on survival of mice in cold

Male albino mice (Swiss-Webster) were raised at 5 °C under short (8L:16D) and long (16L:8D) light periods. All mice were housed in groups of three to five individuals in plastic mouse cages (16 × 12 × 28 cm) until 42 days of age with food and water ad libitum and cold exposed to ?40 °C between 10:00 am and 4:00 pm to determine survival time or time until loss of righting response occurred (CT min). Under short photo-periods, survival time was 49.3 ± 4.4 min and under long photoperiods it was 38.7 ± 1.9 min (P < 0.05). A second group of mice was maintained from birth at thermoneutral temperature (22 °C) under constant darkness, short day lengths (4L:20D), or constant light in the same fashion as mentioned above. When exposed to ?20 °C survival time was found to be 80.0 ± 5.0 min for the animals kept in constant darkness, 61.1 ± 2.3 min for animals raised in short photo-periods (4L:20D) (P < 0.01), and 52.4 ± 2.3 min for mice raised in constant light (P < 0.05). After 30 min mean rectal temperature was 32.1 ± 0.47 °C for constant-darkness animals, 30.5 ± 0.43 °C for short-day animals (P < 0.02), and 28.5 ± 0.74 °C for animals raised in constant light (P < 0.05). After 60 min mean rectal temperatures for constant-dark, 4L:20D, and constant-light animals were compared and body temperature was found to be 23.7 ± 1.6, 17.3 ± 1.5 (P < 0.01), and 12.8 ± 0.87 °C (P < 0.05), respectively. From these data, it is obvious that photoperiod influences cold resistance at both cold and thermoneutral acclimation temperatures although when considered individually, cold acclimation enhances cold survival to a greater degree than does reduced light exposure.     

Temperatures in Pigs During 3 T MRI Temperatures,Heart Rates,and Breathing Rates of Pigs During RF Power Deposition in a 3 T (128 MHz) Body Coil

Exposure to radiofrequency (RF) power deposition during magnetic resonance imaging (MRI) induces elevated body‐tissue temperatures and may cause changes in heart and breathing rates, disturbing thermoregulation. Eleven temperature sensors were placed in muscle tissue and one sensor in the rectum (measured in 10 cm depth) of 20 free‐breathing anesthetized pigs to verify temperature curves during RF exposure. Tissue temperatures and heart and breathing rates were measured before, during, and after RF exposure. Pigs were placed into a 60‐cm diameter whole‐body resonator of a 3 T MRI system. Nineteen anesthetized pigs were divided into four RF exposure groups: sham (0 W/kg), low‐exposure (2.7 W/kg, mean exposure time 56 min), moderate‐exposure (4.8 W/kg, mean exposure time 31 min), and high‐exposure (4.4 W/kg, mean exposure time 61 min). One pig was exposed to a whole‐body specific absorption rate (wbSAR) of 11.4 W/kg (extreme‐exposure). Hotspot temperatures, measured by sensor 2, increased by mean 5.0 ± 0.9°C, min 3.9; max 6.3 (low), 7.0 ± 2.3°C, min 4.6; max 9.9 (moderate), and 9.2 ± 4.4°C, min 6.1, max 17.9 (high) compared with 0.3 ± 0.3°C in the sham‐exposure group (min 0.1, max 0.6). Four time‐temperature curves were identified: sinusoidal, parabolic, plateau, and linear. These curve shapes did not correlate with RF intensity, rectal temperature, breathing rate, or heart rate. In all pigs, rectal temperatures increased (2.1 ± 0.9°C) during and even after RF exposure, while hotspot temperatures decreased after exposure. When rectal temperature increased by 1°C, hotspot temperature increased up to 42.8°C within 37 min (low‐exposure) or up to 43.8°C within 24 min (high‐exposure). Global wbSAR did not correlate with maximum hotspot. Bioelectromagnetics. 2021;42:37–50. © 2020 The Authors. Bioelectromagnetics published by Wiley Periodicals LLC on behalf of Bioelectromagnetics Society     

Effects of alternating exposure to cold and heat for 14 days on cold tolerance in winter

People are exposed to heat regularly due to their jobs or daily habits in cold winter, but few studies have reported whether parallel heat and cold exposure and diminish cold acclimation. This study was conducted to investigate the effects of alternating exposure to cold and heat on cold tolerance in eight young males. A daily acclimation program to cold and heat, which consisted of 2-h sitting at 10 °C air in the morning and 2-h running and rest at 30 °C air in the afternoon, was conducted for 14 consecutive days. Eight male subjects participated in a cold tolerance test (10 °C [ ± 0.3], 40%RH[ ± 3]) before (PRE) and after (POST) completing the alternating exposure program. During the cold tolerance test, subjects remained sitting upright on a chair for 60 min. Rectal temperature (T_re) was lower in POST than in PRE during the 60-min cold tolerance test (P = 0.027). During the cold tolerance test, systolic, diastolic, and mean arterial blood pressures in POST were lower than those in PRE (P = 0.006, P = 0.005, and P = 0.004). No significant differences in skin temperatures between PRE and POST were found for the cold tolerance test. There were no significant differences in energy expenditure during cold exposure between PRE and POST. Subjects felt less cold in POST than in PRE (P = 0.013) whereas there was no significant difference in overall thermal comfort between PRE and POST. These results suggest that cold adaptation can still occur in the presence of heat stress.     

Responses of the bed bug,Cimex lectularius,to temperature extremes and dehydration: levels of tolerance,rapid cold hardening and expression of heat shock proteins

This study of the bed bug, Cimex lectularius, examines tolerance of adult females to extremes in temperature and loss of body water. Although the supercooling point (SCP) of the bed bugs was approximately −20°C, all were killed by a direct 1 h exposure to −16°C. Thus, this species cannot tolerate freezing and is killed at temperatures well above its SCP. Neither cold acclimation at 4°C for 2 weeks nor dehydration (15% loss of water content) enhanced cold tolerance. However, bed bugs have the capacity for rapid cold hardening, i.e. a 1‐h exposure to 0°C improved their subsequent tolerance of −14 and −16°C. In response to heat stress, fewer than 20% of the bugs survived a 1‐h exposure to 46°C, and nearly all were killed at 48°C. Dehydration, heat acclimation at 30°C for 2 weeks and rapid heat hardening at 37°C for 1 h all failed to improve heat tolerance. Expression of the mRNAs encoding two heat shock proteins (Hsps), Hsp70 and Hsp90, was elevated in response to heat stress, cold stress and during dehydration and rehydration. The response of Hsp90 was more pronounced than that of Hsp70 during dehydration and rehydration. Our results define the tolerance limits for bed bugs to these commonly encountered stresses of temperature and low humidity and indicate a role for Hsps in responding to these stresses.     

Thermal tolerance of dried shoots of the moss Bryum argenteum

We conducted laboratory experiments to determine the lethal temperatures of the shoots of dried Bryum argenteum and to determine how this restoration species responds to extreme environments. We specifically assessed changes in gene expression levels in the shoots of dried B. argenteum plants that were subjected to sudden heat shock (control (20 ± 2°C), 80°C, 100°C, 110°C or 120°C) followed by exposure to heat for an additional 10, 20, 30 or 60 min. After they were exposed to heat, the samples were placed in wet sand medium, and their survival and regeneration abilities were evaluated daily for 56 days. The results showed that lethal temperatures significantly reduced the shoot regeneration potential, delayed both shoot and protonemal emergence times and reduced the protonemal emergence area. In addition, the expression of nine genes (HSF3, HSP70, ERF, LEA, ELIP, LHCA, LHCB, Tr288 and DHN) was induced by temperature stress, as assessed after 30 min of exposure. Additionally, a new thermal tolerance level for dried B. argenteum – 120°C for 20 min – was determined, which was the highest temperature recorded for this moss; this tolerance exceeded the previous record of 110°C for 10 min. These findings help elucidate the survival mechanism of this species under heat shock stress and facilitate the recovery and restoration of destroyed ecosystems.     

Thermal acclimation of broiler birds by intermittent heat exposure

Heat stress impairs the performance of broilers which increases the economic losses. Effect of duration of heat exposure on performance and acclimatory responses in broiler birds was investigated. At 21 d of age 160 Hubbard birds (80 males+80 females) were equally distributed into 5 treatments (T). The T1, T2, T3 and T4 were acclimated by daily exposure to heat (38±1 °C, 62±2% RH) for 1, 2, 3 and 4 h/d, respectively, for 14 d. T0 was the non-acclimated control (kept at 22±2 °C, 65±2% RH). At 36 d of age the thermotolerance of all birds was evaluated under simulated heat wave conditions by exposing them to an acute heat stress (43±1 °C, 55±3% RH) for 4 h. Body weight (BW), average daily gain (ADG) and average daily feed intake (ADFI) were not affected in T2 and T3, while T3 and T4 showed significant reductions in BW, ADG and ADFI compared to the control. Daily changes in ADFI/kg of metabolic BW (ADFI/BW^0.75), rectal temperature (Tr), rate of increase in rectal temperature (RITr) and evaporative water loss (EWL) showed biphasic patterns of acclimatory responses. The 2 phases were distinctly differentiated by plateau days. Phase 1 characterized by a sharp decline in ADFI/BW^0.75 followed by a gradual increase until the plateau, while Tr, RITr and EWL increased sharply followed by gradual decreases until the plateau. Beyond the plateau (phase 2), homeostatic responses in ADFI/BW^0.75, Tr, RITr and EWL were observed toward the end of the study. Acclimated birds were able to withstand the simulated heat wave with 0% mortality, lower Tr, and longer survival time compared to the control. In conclusion, acclimation could protect birds from acute heat waves and associated heat stress mortality until marketing age. However, applicability of these results towards the industry needs further investigations.     

Stressor interactions in freshwater habitats: Effects of cold water exposure and food limitation on early‐life growth and upper thermal tolerance in white sturgeon,Acipenser transmontanus

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Fan-precooling effect on heat strain while wearing protective clothing

This study compared heat strain during walking while wearing impermeable protective suits between fan-precooling and nonprecooling conditions. Six males engaged in 60 min of walking at a moderate speed (～2.5 km/h) in a hot environment (37 °C, 40 % relative humidity). Fanning using a fan (4.5 m/s) and spraying water over the body before wearing the suits produced significantly lower rectal temperature before the walking (37.3?±?0.1 °C vs. 37.0?±?0.1 °C, P?P?相似文献   

Temperature preferences of the mite, Alaskozetes antarcticus, and the collembolan, Cryptopygus antarcticus from the maritime Antarctic

Abstract. The thermal preferences of Alaskozetes antarcticus (Acari, Cryptostigmata) and Cryptopygus antarcticus (Collembola, Isotomidae) were investigated over 6 h within a temperature gradient (?3 to +13 °C), under 100% relative humidity (RH) conditions. After 10 days of acclimation at ?2 or +11 °C, individual supercooling points (SCP) and thermopreferences were assessed, and compared with animals maintained for 10 days under fluctuating field conditions (?6 to +7 °C). Acclimation at ?2 °C lowered the mean SCP of both A. antarcticus (?24.2 ± 9.1) and C. antarcticus (?14.7 ± 7.7) compared to field samples (?19.0 ± 9.0 and ?10.7 ± 5.2, respectively). Acclimation at +11 °C increased A. antarcticus mean SCP values (?13.0 ± 8.5) relative to field samples, whereas those of C. antarcticus again decreased (?16.7 ± 9.1). Mites acclimated under field conditions or at +11 °C selected temperatures between ?3 and +1 °C. After acclimation at ?2 °C, both species preferred +1 to +5 °C. Cryptopygus antarcticus maintained under field conditions preferred +5 to +9 °C, whereas individuals acclimated at +11 °C selected +9 to +13 °C. For A. antarcticus, thermopreference was not influenced by its cold hardened state. The distribution of field specimens was further assessed within two combined temperature and humidity gradient systems: (i) 0–3 °C/12% RH, 3–6 °C/33% RH, 6–9 °C/75% RH and 9–12 °C/100% RH and (ii) 0–3 °C/100% RH, 3–6 °C/75% RH, 6–9 °C/33% RH and 9–12 °C/12% RH. In gradient (i), C. antarcticus distributed homogeneously, but, in gradient (ii), C. antarcticus preferred 0–3 °C/100% RH. Alaskozetes antarcticus selected temperatures between 0 and +6 °C regardless of RH conditions. Cryptopygus antarcticus appears better able than A. antarcticus to opportunistically utilize developmentally favourable thermal microclimates, when moisture availability is not restricted. The distribution of A. antarcticus appears more influenced by temperature, especially during regular freeze‐thaw transitions, when this species may select low temperature microhabitats to maintain a cold‐hardened state.     

Differences in cold tolerance,desiccation resistance,and cryoprotectant production between three populations of <Emphasis Type="Italic">Eurosta solidaginis</Emphasis> collected from different latitudes

Possible links between cold-tolerance and desiccation resistance were examined between larvae of the goldenrod gall fly collected from Michigan, southern Ohio, and Alabama locations as their host plant senesced. After acclimation to 5°C, Michigan-collected larvae were more cold-tolerant (25% survival after a 96 h exposure to −40°C) than larvae from Ohio (10% survival) and Alabama (0% survival). Increased cold-tolerance was partially linked to higher concentrations of the cryoprotectant glycerol (Michigan: 500 ± 30 mmol; Ohio: 270 ± 20; Alabama: 220 ± 20). Moreover, cryoprotectants may have functioned to reduce rates of overall and cuticular water loss for Michigan larvae, 0.10 ± 0.01 and 0.037 ± 0.003 μg mm⁻² h⁻¹, respectively, values that were 40-44% lower than those for Ohio and Alabama larvae and may represent a link between desiccation resistance and cold-tolerance. After acclimation to 20°C, Alabama-collected larvae had metabolic rates that were 40% lower than those from Ohio and Michigan that averaged 0.100 ± 0.006 μl of CO₂ produced g⁻¹ h⁻¹. The lower metabolic rate of Alabama-collected larvae at 20°C likely resulted in reduced respiratory transpiration that may represent a mechanism to maintain water balance at the higher overwintering temperatures they typically experience.     

Supplemental intermittent-day heat training and the lactate threshold

Heat acclimation over consecutive days has been shown to improve aerobic-based performance. Recently, it has been suggested that heat training can improve performance in a temperate environment. However, due to the multifactorial training demands of athletes, consecutive-day heat training may not be suitable. The current study aimed to investigate the effect of brief (8×30 min) intermittent (every 3–4 days) supplemental heat training on the second lactate threshold point (LT₂) in temperate and hot conditions. 21 participants undertook eight intermittent-day mixed-intensity treadmill exercise training sessions in hot (30 °C; 50% relative humidity [RH]) or temperate (18 °C; 30% RH) conditions. A pre- and post-incremental exercise test occurred in temperate (18 °C; 30% RH) and hot conditions (30 °C; 50% RH) to determine the change in LT₂. The heat training protocol did not improve LT₂ in temperate (Effect Size [ES]±90 confidence interval=0.10±0.16) or hot (ES=0.26±0.26) conditions. The primary finding was that although the intervention group had a change greater than the SWC, no statistically significant improvements were observed following an intermittent eight day supplemental heat training protocol comparable to a control group training only in temperate conditions. This is likely due to the brief length of each heat training session and/or the long duration between each heat exposure.     

Involvement of nitric oxide in acquired thermotolerance of rice seedlings

The role of nitric oxide (NO) in thermotolerance acquired by heat acclimation (38°C) was investigated. Results showed that 38°C acclimation, on the one hand, obviously reduced hydrogen peroxide (H₂O₂) and MDA contents and ion leakage degree in rice leaves; however, on the other hand, it increased the survival of rice (Oryza sativa L.) seedlings under 50°C heat stress. Application of nitric oxide donor, sodium nitroprusside (SNP), prior to 38°C acclimation dramatically increased the acquired thermotolerance. To elucidate the role of endogenous NO in acquired thermotolerance, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO, a specific NO scavenger) was used (scavengers are used to control the level of both exogenous and endogenous NO). Results showed that PTIO pretreatment resulted in the elimination of acquired thermotolerance induced by 38°C acclimation in rice seedlings. Nitric oxide (NO) release measurement indicated that there was indeed an abrupt elevation in the NO content in 40 min after 38°C acclimation, proving the involvement of NO in acquired thermotolerance inducement in rice seedling.     

Water stress preconditioning and cotton root pressure-flux relationships

Summary A model was developed to describe interactive effects of exposure time and treatment on thermostability of excisedIllicium parviflorum Michx. root cell membranes using electrolyte leakage (L_c) procedures. Roots were moved from 25°C to treatment temperatures between 35°C and 60°C for 30 to 300 min. A sigmoidal response described L_c increases with increasing temperature at selected time exposures and the lethal exposure time decreased exponentially as temperature increased. The lethal temperature (52.0±1.1°C) for a 15 min exposure using this technique was comparable to the critical temperature (52.2±1.2°C) when roots were exposed to gradually increasing temperatures (4°C per h). Total protein content of roots began to decrease as temperatures increased from 35 to 40°C and the temperature corresponding to 50% reduction in total proteins was 49.1±2.2°C.