Effects Of Short-term Heat Stress Research Articles

Quantifying the Individual and Combined Effects of Short-Term Heat Stress at Booting and Flowering Stages on Nonstructural Carbohydrates Remobilization in Rice

Rice production is threatened by climate change, particularly heat stress (HS). Nonstructural carbohydrates (NSCs) remobilization is a key physiological mechanism that allows rice plants to cope with HS. To investigate the impact of short-term HS on the remobilization of nonstructural carbohydrates (NSCs) in rice, two cultivars (Huaidao-5 and Wuyunjing-24) were subjected to varying temperature regimes: 32/22/27 °C as the control treatment, alongside 40/30/35 °C and 44/34/39 °C, for durations of 2 and 4 days during the booting, flowering, and combined stages (booting + flowering) within phytotrons across the years 2016 and 2017. The findings revealed that the stem’s NSC concentration increased, while the panicle’s NSCs concentration, the efficiency of NSCs translocation from the stem, and the stem NSC contribution to grain yield exhibited a consistent decline. Additionally, sugar and starch concentrations increased in leaves and stems during late grain filling and maturity stages, while in panicles, the starch concentration decreased and sugar concentration increased. The heat-tolerant cultivar, Wuyunjing-24, exhibited higher panicle NSC accumulation under HS than the heat-sensitive cultivar, Huaidao-5, which had more stem NSC accumulation. The flowering stage was the most vulnerable to HS, followed by the combined and booting stages. Heat degree days (HDDs) were utilized to quantify the effects of HS on NSC accumulation and translocation, revealing that the flowering stage was the most affected. These findings suggest that severe HS makes the stem the primary carbohydrate storage sink, and alleviation under combined HS aids in evaluating NSC accumulation, benefiting breeders in developing heat-tolerant rice varieties.

Immune and Reproductive Biomarkers in Female Sea Urchins Paracentrotus lividus under Heat Stress.

The functioning of the immune and reproductive systems is crucial for the fitness and survival of species and is strongly influenced by the environment. To evaluate the effects of short-term heat stress (HS) on these systems, confirming and deepening previous studies, female sea urchin Paracentrotus lividus were exposed for 7 days to 17 °C, 23 and 28 °C. Several biomarkers were detected such as the ferric reducing power (FRAP), ABTS-based total antioxidant capacity (TAC-ABTS), nitric oxide metabolites (NOx), total thiol levels (TTL), myeloperoxidase (MPO) and protease (PA) activities in the coelomic fluid (CF) and mitochondrial membrane potential (MMP), H2O2 content and intracellular pH (pHi) in eggs and coelomocytes, in which TAC-ABTS and reactive nitrogen species (RNS) were also analyzed. In the sea urchins exposed to HS, CF analysis showed a decrease in FRAP levels and an increase in TAC-ABTS, TTL, MPO and PA levels; in coelomocytes, RNS, MMP and H2O2 content increased, whereas pHi decreased; in eggs, increases in MMP, H2O2 content and pHi were found. In conclusion, short-term HS leads to changes in five out of the six CF biomarkers analyzed and functional alterations in the cells involved in either reproductive or immune activities.

Effects of short-term heat stress on the activity of three antioxidant enzymes of predatory mite Neoseiulus barkeri (acari, phytoseiidae).

To study the physiological mechanisms of Neoseiulus barkeri in response to short-term heat stress, the eggs and the emerged adults were exposed to 38, 40, and 42°C, 85% ± 5%RH,16 h:8 h (L:D) for 2, 4, and 6 h. The activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) as well as the protein content of N. barkeri were examined. All treatments caused significant different changes compared to the untreated control. The protein content increased as the temperature increased, while it showed different changing trends with the prolongation of exposure duration. The enzymatic activity of SOD, CAT, and POD was significantly affected by the temperature treatment. Both the maximum and minimum level of the three enzymes after a short-term heat stress differed significantly to the control group (p < 0.05). The highest values of three enzymatic activities were all obtained at 40°C-4 h. Person correlation analysis indicates that the high temperature was the primary factor affecting the enzymatic activity, while the exposure duration of the heat stress was the secondary factor. In general, the short-term heat stress increased the protein content of Neoseiulus barkeri and up-regulated the expression of SOD, CAT, and POD activities as well.

Developmental timing of extreme temperature events (heat waves) disrupts host-parasitoid interactions.

When thermal tolerances differ between interacting species, extreme temperature events (heat waves) will alter the ecological outcomes. The parasitoid wasp Cotesia congregata suffers high mortality when reared throughout development at temperatures that are nonstressful for its host, Manduca sexta. However, the effects of short‐term heat stress during parasitoid development are unknown in this host–parasitoid system.Here, we investigate how duration of exposure, daily maximum temperature, and the developmental timing of heat waves impact the performance of C. congregata and its host¸ M. sexta. We find that the developmental timing of short‐term heat waves strongly determines parasitoid and host outcomes.Heat waves during parasitoid embryonic development resulted in complete wasp mortality and the production of giant, long‐lived hosts. Heat waves during the 1st‐instar had little effect on wasp success, whereas heat waves during the parasitoid's nutritionally and hormonally critical 2nd instar greatly reduced wasp emergence and eclosion. The temperature and duration of heat waves experienced early in development determined what proportion of hosts had complete parasitoid mortality and abnormal phenotypes.Our results suggest that the timing of extreme temperature events will be crucial to determining the ecological impacts on this host–parasitoid system. Discrepancies in thermal tolerance between interacting species and across development will have important ramifications on ecosystem responses to climate change.

Short-term high nighttime temperatures pose an emerging risk to rice grain failure

Under currently projected global warming, heat waves are expected to become more frequent, and crops will be exposed to more extreme heat events during both day and night periods. It is well known that high daytime temperatures during flowering induce spikelet sterility in rice plants and directly reduce yields. However, the effects of short-term heat stress at night have not been well documented. Here, we investigated the effects of 1- to 3-night high nighttime temperatures at anthesis on rice spikelet fertility. We found that a single night high temperature of ∼32 °C just before anthesis induced spikelet sterility even in the absence of high daytime temperature. Fertile grain number was significantly decreased by a 3-night exposure to high temperatures of ≥30 °C, much lower than the reported threshold of 35 °C for heat-induced sterility during the daytime. Moreover, high nighttime temperature substantially exacerbated the sterility induced by high daytime temperature. These results indicate that short periods of high nighttime temperatures, which may be experienced during heat waves, will increase the risk of heat damage to rice yield and increase the uncertainty in predictions of future rice production. Sensitivity to high nighttime temperature differed among cultivars but was positively correlated with their sensitivity to high daytime temperatures. This suggests that concurrent improvement of tolerance to daytime and nighttime high temperatures may be possible through breeding.

Effects of elevated temperature on prooxidant-antioxidant homeostasis and redox status in the American oyster: Signaling pathways of cellular apoptosis during heat stress

Increasing seawater temperature affects growth, reproduction, development, and various other physiological processes in aquatic organisms, such as marine invertebrates, which are especially susceptible to high temperatures. In this study, we examined the effects of short-term heat stress (16, 22, 26, and 30 °C for 1-week exposure) on prooxidant-antioxidant homeostasis and redox status in the American oyster (Crassostrea virginica, an edible and commercially cultivated bivalve mollusk) under controlled laboratory conditions. Immunohistochemical and real-time quantitative PCR (qRT-PCR) analyses were performed to examine the expression of heat shock protein-70 (HSP70, a biomarker of heat stress), catalase (CAT, an antioxidant), superoxide dismutase (SOD, an antioxidant), dinitrophenyl protein (DNP, a biomarker of reactive oxygen species, ROS), and 3-nitrotyrosine protein (NTP, an indicator of reactive nitrogen species, RNS), in the gills and digestive glands of oysters. In situ TUNEL assay was performed to detect cellular apoptosis in tissues. Histological analysis showed an increase in mucus secretion in the gills and digestive glands of oysters exposed to higher temperatures (22, 26, and 30 °C) compared to control (16 °C). Immunohistochemical and qRT-PCR analyses showed significant increases in HSP70, DNP and NTP protein, and mRNA expressions in tissues at higher temperatures. Cellular apoptosis was also significantly increased at higher temperatures. Thus, heat-induced oxidative and nitrative stress likely occur due to overproduction of ROS and RNS. Interestingly, expression of CAT and SOD increased in oysters exposed to 22 and 26 °C, but was at or below control levels in the highest temperature exposure (30 °C). Collectively, these results suggest that elevated seawater temperatures cause oxidative/nitrative stress and induce cellular apoptosis through excessive ROS and RNS production, leading to inhibition of the antioxidant defense system in marine mollusks.

Short-term heat stress at booting stage inhibited nitrogen remobilization to grain in rice

Extreme heat-stress events have become more frequent due to climate change often with devastating effects on rice production. Accumulation and translocation of nitrogen (N) in rice organs is an important process that determines rice yield and quality. To assess the effects of short-term heat stress during booting stage on the accumulation and remobilization of N in rice plant organs, a pot-experiment in phytotron chambers was conducted using two cultivars (Nanjing 41 and Wuyunjing 24) at mean temperatures of 27 °C, 31 °C, 35 °C and 39 °C for 2, 4 and 6 days at booting stage. The results showed that high temperatures of 35 °C and 39 °C for 4 and 6 days significantly increased N concentration in leaves, stems, panicles and grains. Severe heat stress strongly reduced N translocation from leaves and stems into grains, resulting in an increased N distribution in stems and leaves. Moreover, N translocation efficiency of the vegetative parts decreased with increasing heat degree-days (HDD), and when HDD > 21.5 °C d, N translocation efficiency was negative, indicating re-accumulation of N in vegetative organs under severe heat stress. N concentration in leaves was positively associated with photosynthetic rate. Dry matter partitioning index of leaves and stems was positively correlated with their N concentration, whereas grain dry matter partitioning index was negatively correlated with grain N concentration. Heat stress reduced the ratio of grain number to leaf area, thereby reducing the proportion of sink to source. These results suggested that the low N translocation efficiency under heat stress could be due to a decrease in sink capacity. Our findings demonstrate that projected climate warming is likely to induce a significant reduction in N accumulation in rice grains by inhibiting the translocation of N from vegetative organs to grains.

Quantifying the effects of short-term heat stress at booting stage on nonstructural carbohydrates remobilization in rice

Extreme heat stress events are becoming more frequent under anticipated climate change, which can have devastating impacts on rice growth and yield. To quantify the effects of short-term heat stress at booting stage on nonstructural carbohydrates (NSC) remobilization in rice, two varieties (Nanjing 41 and Wuyunjing 24) were subjected to 32/22/27 °C (maximum/minimum/mean), 36/26/31 °C, 40/30/35 °C, and 44/34/39 °C for 2, 4 and 6 days in phytotrons at booting stage during 2014 and 2015. Yield and yield components, dry matter partitioning index (DMPI), NSC accumulation and translocation were measured and calculated. The results showed that the increase of high-temperature level and duration significantly reduced grain yield by suppressing spikelet number per panicle, seed-setting rate, and grain weight. Heat stress at booting decreased DMPI in panicles, increased DMPI in stems, but had no significant effect on photosynthetic rate. Stem NSC concentration increased whereas panicles NSC concentration, stem NSC translocation efficiency, and contribution of stem NSC to grain yield decreased. Severe heat stress even transformed the stem into a carbohydrate sink during grain filling. The heat-tolerant Wuyunjing 24 showed a higher NSC transport capacity under heat stress than the heat-sensitive Nanjing 41. Heat degree-days (HDD), which combines the effects of the intensity and duration of heat stress, used for quantifying the impacts of heat stress indicates the threshold HDD for the termination of NSC translocation is 9.82 °C day. Grain yield was negatively correlated with stem NSC concentration and accumulation at maturity, and yield reduction was tightly related to NSC translocation reduction. The results suggest that heat stress at booting inhibits NSC translocation due to sink size reduction. Therefore, genotypes with higher NSC transport capacity under heat stress could be beneficial for rice yield formation.

Effects of short-term heat stress at booting stage on rice-grain quality

Extreme heat-stress events are becoming more frequent under anticipated global warming, which is having devastating effect on grain yield, as well as quality, of rice (Oryza sativa L.). The effects of heat stress at booting stage on grain quality of two japonica varieties, Nanjing41 and Wuyunjing24, were investigated in phytotrons during 2014 and 2015. Rice plants were subjected to four mean temperature regimes 27°C, 31°C, 35°C and 39°C of 2, 4 and 6 days’ duration. The results showed that high temperatures of 35°C and 39°C for 4 and 6 days significantly reduced panicle size, seed-setting rate, grain size, chalky grain rate, milling characteristics and amylose content, but increased protein content. Severe heat stress decreased values of peak viscosity and breakdown, and increased pasting temperature. An increase in heat degree-days decreased the percentage of chalky grains exponentially, and decreased amylose content and increased protein content linearly. Sensitivity of grain quality to heat stress in the two varieties differed among quality traits and with heat stress intensity. This study indicates that rice-grain quality had some resistance to mild heat stress, but it could not withstand severe heat stress at booting. Short-term heat stress at booting stage deteriorates most grain-quality traits, posing a potential risk to rice quality. The impacts on grain quality could be well quantified by the combined effects of the intensity and duration of heat stress at booting stage.

Effects of short-term heat stress on PSII and subsequent recovery for senescent leaves of Vitis vinifera L. cv. Red Globe

Heat stress occurs frequently in energy-saving sunlight greenhouses (ESSG) at the late growth stage. Three-year delayed cultivation (DC) of the Red Globe cultivar of Vitis vinifera L. was used to clarify the physiological mechanisms of short-term heat stress on PSII and subsequent recovery from heat stress. By November, the photosynthetic function had declined and the fall in transpiration rate (E) with heating time increased the possibility of heat damage. In July, the most obvious increase was in the relative variable fluorescence at J point at 40°C, and in November it changed to K point. The 5 min of heat treatment resulted in a significant increase of the relative variable fluorescence at 0.3 ms (Wk), and after 10 min of heat treatment, the number of reactive centres per excited cross section (RC/CSo), probability that a trapped exciton moves an electron into the electron transport chain beyond QA− (at t=0) (ψo) and quantum yield of electron transport at t=0 (ϕEo) decreased significantly (P<0.05), suggesting that the reaction centre, donor and acceptor side of photosystem II (PSII) were all significantly inhibited (P<0.05) and that the thermal stability of the photosynthetic mechanism was reduced. The inhibition of energy fluxes for senescent leaves in November was earlier and more pronounced than that for healthy leaves, which did not recover from heat stress of more than 15 min after 2 h recovery at room temperature.

Effect of short-term heat stress prior to flowering and early grain set on the grain yield of wheat

Short periods of heat stress in spring under Mediterranean climate can have large effects on crop yields. Most studies on heat stress have focused on crop responses to extended periods of high temperature under controlled environment conditions. There is limited information on the effects of short periods of heat stress on the yield of wheat. Therefore, field and controlled environment studies were undertaken to determine the effects of short-term heat stress on flag leaf senescence, as well as grain yield and its components. Wheat genotypes were exposed to heat stress for a single-day at two different stages: (H1) near flowering or green anther stage and (H2) early grain set or 7–10 days after anthesis (DAA) in 2009 and 2010. Heat treatment was applied in the field in a portable purpose-built heat chamber in which the temperature was steadily increased to a maximum of 35°C, which was maintained for 3h before being allowed to steadily decrease to the ambient temperature, like a typical spring heat event. Similar to the field studies, wheat genotypes were also exposed to a single-day heat event (35°C maximum) in the controlled environment (CE) study. This single-day heat stress event caused a significant reduction in grain yield and yield components in both years. Heat stress (H1 or H2) accelerated the rate of loss of flag leaf chlorophyll content. A higher rate of senescence in 2009, which was warmer and drier than 2010, was associated with greater yield loss. Reduction in grain yield among the genotypes was negatively correlated (r=−0.79; p<0.001) with the rate of flag leaf senescence. Heat stress reduced post-heading duration and grain yield across genotypes and heat stress treatments was strongly correlated (r=0.80; p<0.001 in 2009 and r=0.82; p<0.001 in 2010) with post-heading duration. There was also a significant (p<0.001) positive correlation between wheat grain yield and grain number m−2 (2009: r=0.79 and 2010: r=0.70) and wheat grain yield and individual grain mass (IGM) at harvest (r=0.70 in 2009 and r=0.82 in 2010). Standardized partial regression coefficient (b) showed that of the two yield components the contribution of grain number (b=0.786) to the grain yield was higher than IGM (b=0.435) in 2009. In contrast, IGM (b=0.665) appeared to be a stronger contributor to the grain yield than grain number (b=0.443) in 2010. Grain yield loss of different wheat genotypes was strongly correlated (r=0.91; p<0.001) between the field and CE. The results of these studies showed that under field and CE conditions, Janz was consistently the most sensitive genotype to heat stress. In contrast, CM9-6Y, CM9-4Y and Krichauff appeared to be most tolerant to heat stress. Averaged over the two growing seasons and heat stress treatments, the reduction in grain yield was greater in Janz (25%) than in CM9-6Y and CM9-4Y (13% each), followed by Krichauff (16%) and Excalibur (18%). It could be suggested that early headed wheat genotypes with slower rate of leaf senescence after heat exposure and longer post-heading duration could be more tolerant to heat stress.

Effect of short-term heat stress prior to flowering and at early grain set on the utilization of water-soluble carbohydrate by wheat genotypes

In Mediterranean environments, cereal crops are often exposed to short periods of elevated temperatures in spring when crops are approaching flowering and grain filling. Stem water-soluble carbohydrate (WSC) could be an important carbon bank for supporting grain filling in wheat especially when carbon assimilation is hampered by heat stress. However, there is relatively little information available in the literature on the effects of short periods of heat stress on grain growth and the importance of WSC in mitigating the effects of heat stress. Therefore, field and controlled environment studies were undertaken to determine the effects of short-term heat stress on the peduncle WSC content and its contribution to grain size of wheat in the field. Wheat genotypes were exposed to heat stress on a single-day at two different stages: (H1) near flowering or green anther stage and (H2) early grain set or 7–10 days after anthesis (DAA). On each occasion crops were enclosed in a portable heat chamber and the temperature was gradually increased to a maximum of 35°C. This single day heat stress event caused a significant reduction in individual grain mass (IGM) and grain number in both years. There was no discernible change in IGM until 14 days postanthesis, after which time grain growth in the heat-stressed plants was reduced. On average, as compared to the unheated control, the reductions in IGM in wheat genotypes ranged from 10 to 25%. The maximum WSC content was reduced by heat stress in all wheat genotypes. Heat stress (average of H1 and H2) reduced peduncle WSC content by 26% and mobilized WSC content by 15% across all studies. Mobilization of peduncle WSC content was also significantly reduced by the heat stress treatments and mobilization appeared to start at 21 days postanthesis when the grain was about one third of the final mass. IGM of wheat genotypes with higher maximum peduncle WSC content showed lower sensitivity to heat stress in both years of this study (H1: r=−0.82; p<0.001 and H2: r=−0.84; p<0.001). Over both seasons, heat stress treatments (H1, H2) and all genotypes, greater mobilized WSC was associated with increased grain size (r=0.70; p<0.01). It could be argued that selection of wheat genotypes with higher stem WSC reserves and greater mobilization of WSC could be used to buffer grain growth and development under heat stress conditions, which are a common occurrence in the Australian wheat belt.

The effects of heat stress on physical functioning in persons with multiple sclerosis

Heat sensitivity is a well-recognised feature in multiple sclerosis (MS). However, little is known about how heat affects physical performance in persons with MS. The objective of the study was to evaluate the effects of short-term heat stress on physical functioning in persons with MS. Twenty-three heat-sensitive MS subjects and 19 healthy controls participated. Moderate heat exposure took place in a dry Finnish sauna. Measures of upper and lower extremity function, static and dynamic balance, and walking capacity were applied. Core body temperature was measured by a telemetric physiological monitoring system. Assessments were conducted before, immediately, 1hour, and 1day after the heat exposure. Subjects with MS showed a significantly (P=0.002) higher core body temperature than the controls following the heat stress. Performances in walking (P<0.001), chair rise (P=0.005) and functional reach (P=0.04) were poorer in MS subjects than in controls immediately after the heat. No prolonged heat effects were observed. An increase in ambient temperature causes a higher core body temperature rise in MS subjects than in healthy controls. This rise in temperature is associated with acute, but not prolonged detrimental effects on physical functioning.

The effects of heat stress on cognition in persons with multiple sclerosis

Background: Heat sensitivity and cognitive deficits are typical manifestations of multiple sclerosis (MS). Although cognitive deficits are quite well characterized, practically no data exist on the effects of heat on cognitive performances in MS. Objective: To assess the effects of short-term heat stress on cognitive functioning in subjects with MS. Methods: A total of 23 heat-sensitive MS and 19 healthy control (HC) subjects participated. Moderate heat exposure took place in a Finnish sauna. Cognitive functioning was measured with tests of sustained attention and processing speed, the Paced Auditory Serial Addition Test (PASAT 3” and 2”) and the computerized visual vigilance test, before, during and after heat exposure. Results: During the heat exposure, the core body temperature of the MS group rose significantly more (p = 0.002) than that of the HC group. The heat stress worsened the performance of the MS group in the PASAT 3” (p = 0.025) but not in the other cognitive measures. The performance in the PASAT 3” was reversed almost to the baseline level only 1- h after the heat exposure. Conclusions: A significant increase in core body temperature during heat stress is associated with a mild and reversible worsening of the PASAT 3” performance, while visual vigilance performance seems to remain almost unaffected.

Effects of short-term heat stress on endophytic ergot alkaloid-induced alterations in rat hepatic gene expression

Exposure to ergot alkaloids in endophyte-infected fescue (E+) is associated with impaired animal productivity, especially during heat stress, which is commonly referred to as fescue toxicosis. To elucidate the pathogenesis of this condition, the effects of short-term heat stress (HS) on hepatic gene expression in rats exposed to endophytic ergot alkaloids were evaluated. Rats implanted with telemetric transmitters to continuously measure core temperature were fed an E+ diet and maintained under thermoneutral (TN) conditions (21 degrees C) for 5 d, followed by TN or 31 degrees C (HS) conditions for 3 d. Feed intake (FI) and BW were monitored daily. The E+ and HS-induced alterations in hepatic genes were evaluated using DNA microarrays and PCR analyses. Hepatic antioxidant enzyme activities, as well as the incidence of apoptosis, were determined. As expected, intake of E+ reduced FI and BW from pretreatment levels under TN conditions, with greater reductions during short-term HS. Genes involved in gluconeogenesis and apoptosis were upregulated, whereas genes associated with oxidative phosphorylation, xenobiotic metabolism, antioxidative mechanisms, immune function, cellular proliferation, and chaperone activity were all downregulated with short-term HS. Hepatocytic apoptosis was increased and antioxidant enzyme activity decreased in the livers of rats exposed to HS. The hypothesized, exacerbating effects of HS on the direct, endophytic toxin-related and indirect, reduced caloric intake-associated alterations in hepatic gene expression were clearly demonstrated in rats and may help to elucidate the pathogenesis of fescue toxicosis in various animal species.

Effects of short-term heat stress on oxidative damage and responses of antioxidant system in Lilium longiflorum

This paper aims to determine the changes in reactive oxygen species (ROS) and the responses of the lily (Lilium longiflorum L.) antioxidant system to short-term high temperatures. Plants were exposed to three levels of heat stress (37°C, 42°C, 47°C) for 10 h when hydrogen peroxide (H2O2) and superoxide (O2−) production rate along with membrane injury indexes, and changes in antioxidants were measured. Compared with the control (20°C), electrolyte leakage and MDA concentration varied slightly after 10 h at 37°C and 42°C, while increased significantly at 47°C. During 10 h at 37°C and 42°C, antioxidant enzyme activities, such as SOD, POD, CAT, APX and GR, were stimulated and antioxidants (AsA and GSH concentrations) maintained high levels, which resulted in low levels of O2− and H2O2 concentration. However, after 10 h at 47°C, SOD, APX, GR activities and GSH concentration were similar to the controls, while POD, CAT activities and AsA concentration decreased significantly as compared with the control, concomitant with significant increase in O2− and H2O2 concentrations. In addition, such heat-induced effects on antioxidant enzymes were also confirmed by SOD and POD isoform, as Cu/ZnSOD maintained high stability under heat stress and the intensity of POD isoforms reduced with the duration of heat stress, especially at 47°C. It is concluded that in lily plants, the oxidative damage induced by heat stress was related to the changes in antioxidant enzyme activities and antioxidants.

Evolutionary and acclimation-induced variation in the heat-shock responses of congeneric marine snails (genus Tegula) from different thermal habitats: implications for limits of thermotolerance and biogeography.

Heat stress sufficient to cause cellular damage triggers the heat-shock response, the enhanced expression of a group of molecular chaperones called heat-shock proteins (hsps). We compared the heat-shock responses of four species of marine snails of the genus Tegula that occupy thermal niches differing in absolute temperature and range of temperature. We examined the effects of short-term heat stress and thermal acclimation on the synthesis of hsps of size classes 90, 77, 70 and 38 kDa by measuring incorporation of (35)S-labeled methionine and cysteine into newly synthesized proteins in gill tissue. Temperatures at which enhanced synthesis of hsps first occurred (T(on)), temperatures of maximal induction of hsp synthesis (T(peak)) and temperatures at which hsp synthesis was heat-inactivated (T(off)) were lowest in two low-intertidal to subtidal species from the temperate zone, T. brunnea and T. montereyi, intermediate in a mid- to low-intertidal species of the temperate zone, T. funebralis, and highest in a subtropical intertidal species from the Gulf of California, T. rugosa. Synthesis of hsps and other classes of protein by T. brunnea and T. montereyi was heat-inactivated at temperatures commonly encountered by T. funebralis during low tides on warm days. In turn, protein synthesis by T. funebralis was blocked at the upper temperatures of the habitat of T. rugosa. Acclimation of snails to 13 degrees C, 18 degrees C and 23 degrees C shifted T(on) and T(peak) for certain hsps, but did not affect T(off). The heat-shock responses of field-acclimatized snails were generally reduced in comparison with those of laboratory-acclimated snails. Overall, despite the occurrence of acclimatory plasticity in their heat-shock responses, genetically fixed differences in T(on), T(peak) and T(off) appear to exist that reflect the separate evolutionary histories of these species and may play important roles in setting their thermal tolerance limits and, thereby, their biogeographic distribution patterns.

Effects of Heat Stress on Day-Old Broiler Chicks

Short-term heat stress can occur when chicks are transported from the hatchery to growing facilities. Two experiments were conducted to determine the possible effects of short-term heat stress on growth and feed conversion of broiler (Hubbard × Hubbard) chicks. The heat stress was accomplished by placing chicks in Jamesway 252 incubators at dry bulb temperatures ranging from 40 to 45 C for variable times. Growth, feed consumption, and mortality were measured for 16 days following the heat stress.Short sublethal heat stress significantly reduced growth rate to 16 days in these experiments without any effect on feed conversion ratio. The results indicate that the hatchery industry should avoid overheating chicks even for periods as short as 1 hr.