Heat Stress Temperature Research Articles

The Improvement of Thermotolerance in Tall Fescue and Perennial Ryegrass by Activating the Antioxidative System

The effect of hydrogen peroxide (H2O2) of low concentration on thermotolerance of tall fescue (Festuca arundinacea cv. Barlexas) and perennial ryegrass (Lolium perenne cv. Accent) was studied following a foliar pretreatment with 10 mM H2O2. Antioxidative enzymes activities and antioxidant content were measured in both cool-season turfgrass cultivars under heat stress (38/30 °C, day/night) and control normal temperature (26/15 °C, day/night). While activities of catalase(CAT), guaiacol peroxidase (POD), ascorbate peroxidase (APX), glutathione reductase (GR) and glutathione-dependent peroxidases (GPX) were enhanced by H2O2pretreatment during heat stress. APX, GR and GPX activities were significantly enhanced during heat stress. These were likely the most important antioxidative enzymes in tall fescue and perennial ryegrass protecting plants against heat stress. The thermotolerance was also concomitant with an increased glutathione pool, as evaluated by the significant increase of the total glutathione pool in two pretreated cultivars. The increase of POD, CAT, APX, GR activities and significant increase of GPX activity prior to the initiation of heat stress in pre-treatment plants suggested a possible role for H2O2as a signaling molecule protecting them against the subsequent heat-induced damage.

Comparative Proteomic Analysis of Lactobacillus plantarum WCFS1 and ΔctsR Mutant Strains Under Physiological and Heat Stress Conditions

Among Gram-positive bacteria, CtsR (Class Three Stress gene Repressor) mainly regulates the expression of genes encoding the Clp ATPases and the ClpP protease. To gain a better understanding of the biological significance of the CtsR regulon in response to heat-shock conditions, we performed a global proteomic analysis of Lactobacillus plantarum WCFS1 and ΔctsR mutant strains under optimal or heat stress temperatures. Total protein extracts from bacterial cells were analyzed by two-dimensional gel fractionation. By comparing maps from different culture conditions and different L. plantarum strains, image analysis revealed 23 spots with altered levels of expression. The proteomic analysis of L. plantarum WCFS1 and ctsR mutant strains confirms at the translational level the CtsR-mediated regulation of some members of the Clp family, as well as the heat induction of typical stress response genes. Heat activation of the putative CtsR regulon genes at transcriptional and translational levels, in the ΔctsR mutant, suggests additional regulative mechanisms, as is the case of hsp1. Furthermore, isoforms of ClpE with different molecular mass were found, which might contribute to CtsR quality control. Our results could add new outlooks in order to determine the complex biological role of CtsR-mediated stress response in lactic acid bacteria.

The effect of different levels of organic and inorganic chromium supplementation on immune function of broiler chicken under heat-stress conditions

SUMMARY A study was conducted using 250 broiler chickens to evaluate the effect of Cr supplementation on the immune responses of heat-stressed broiler chicks. All birds were kept under a heatstress temperature (33 ± 3°C) and divided into 5 treatments, with 5 replicates of 10 birds each. In a completely randomized design, the basal diets were supplemented with 0 (control), 800, or 1,200 ppb of Cr-l-Met and 800 or 1,200 ppb of CrCl3. On d 42, the bursa of Fabricius, spleen, and thymus were collected, weighed, and expressed as grams per 100 g of BW. Antibody titers against Newcastle virus were higher in broilers that received organic Cr supplements at 18 and 30 d of age (P < 0.05). The heterophil-to-lymphocyte ratios decreased in broilers receiving the Cr-l-Met supplements compared with those in other treatments (P < 0.05). The albuminto-globulin ratios were not affected by treatments at 28 d but were increased in the 1,200 ppb of CrCl3 treatment at 42 d (P < 0.05). Serum cortisol concentrations were lower in the 1,200 Cr-l-Met group (P < 0.01), and serum IgG concentrations were higher in this group (P < 0.01). Lymphoid organ weights did not differ between treatment groups. Both the organic and inorganic Cr supplements improved the immune response of broilers under heat-stress conditions, and a more positive effect was observed by addition of 1,200 Cr-l-Met.

High invertase activity in tomato reproductive organs correlates with enhanced sucrose import into, and heat tolerance of, young fruit.

Heat stress can cause severe crop yield losses by impairing reproductive development. However, the underlying mechanisms are poorly understood. We examined patterns of carbon allocation and activities of sucrose cleavage enzymes in heat-tolerant (HT) and -sensitive (HS) tomato (Solanum lycopersicum L.) lines subjected to normal (control) and heat stress temperatures. At the control temperature of 25/20 °C (day/night) the HT line exhibited higher cell wall invertase (CWIN) activity in flowers and young fruits and partitioned more sucrose to fruits but less to vegetative tissues as compared to the HS line, independent of leaf photosynthetic capacity. Upon 2-, 4-, or 24-h exposure to day or night temperatures of 5 °C or more above 25/20 °C, cell wall (CWIN) and vacuolar invertases (VIN), but not sucrose synthase (SuSy), activities in young fruit of the HT line were significantly higher than those of the HS line. The HT line had a higher level of transcript of a CWIN gene, Lin7, in 5-day fruit than the HS line under control and heat stress temperatures. Interestingly, heat induced transcription of an invertase inhibitor gene, INVINH1, but reduced its protein abundance. Transcript levels of LePLDa1, encoding phospholipase D, which degrades cell membranes, was less in the HT line than in the HS line after exposure to heat stress. The data indicate that high invertase activity of, and increased sucrose import into, young tomato fruit could contribute to their heat tolerance through increasing sink strength and sugar signalling activities, possibly regulating a programmed cell death pathway.

The Effect of Different Levels of Organic and Inorganic Chromium Supplementation on Production Performance, Carcass Traits and Some Blood Parameters of Broiler Chicken Under Heat Stress Condition

A total of 250 broilers in a completely randomized design selected to evaluate the effect of different levels of chromium (Cr) supplementation on performance, carcass traits and some blood parameters of heat-stressed broiler chicks. All birds were kept under heat stress temperature (33 ± 3°C) and divided into five treatments groups. Each treatment consisted of five pens with 10 birds in each pen. The basal diets were supplemented with 0ppb (control), 800ppb Cr-L-Met (T(1)), 1,200ppb Cr-L-Met (T(2)) or 800ppb CrCl(3) (T(3)), and 1,200ppb CrCl(3) (T(4)). The feed intake and body mass were measured at 10, 21, and 42days of age. Blood samples were collected from two birds in each replicates to determine biological and hematological values at 28 and 42days of age. There were no significant difference in mass gain and feed conversion of broilers that received Cr supplementations compared with controls. The serum glucose concentration decreased in broilers received organic chromium methionine supplements compared with other treatments groups. Slight but not significant increases were observed in serum high-density lipoprotein (HDL) concentration of treated groups than controls while the mean serum HDL concentration was significantly higher in T(2) group compared with control group. Serum low-density lipoprotein level decreased in broiler received organic Cr supplements (p < 0.05).

Spatial characterization of recent hot summers in Japan with agro-climatic indices related to rice production

The spatiotemporal characteristics of high summertime temperatures, which can cause high-temperature injuries to rice, during the recent period of climatic variability (1978-2010) in Japan were analyzed and quantified by using daily gridded meteorological data with high spatial resolution and GIS data. Several indices based on heat-dose (defined as the cumulative temperature exceeding a certain threshold) were introduced to assess the impact of heat stress on rice production and quality. Specifically, we examined the utility of these indices for evaluating quality declines in rice. Time series of heat-dose indices based on maximum and minimum summertime temperatures showed that heat stress intensity increased remarkably from 1994. Moreover, high values of a heat-dose index based on a daily mean temperature exceeding 26°C during the 20 days after the heading date of rice showed a clear association with a decline in observed rice quality, whereas no clear relationship was apparent between decreased rice quality due to heat stress and average temperature. We also examined the effect of heat stress on spikelet fertility and ripening in the rice cultivar Koshihikari in four representative regions of Japan by using two indices, a heat-dose index based on a daily maximum temperature exceeding 35°C during 7 days around the heading date, and one based on a daily mean temperature exceeding 26°C during the 20 days after heading. The first index showed large interannual variability in the four regions because of its high dependence on the timing of heading.

EFFECTS OF HEAT STRESS AND AGE ON GROWTH PERFORMANCE AND ENDOCRINE STATUS OF MALE RABBIT

The effect of environmental temperature and age on plasma hormonal concentrations of testosterone (T), dihydrotestosterone (DHT}, cortisol (C), triiodothyronine (T3} and thyroxine (T4) were evaluated in 40 male Grimaud rabbits. Twenty animals were reared at 20ºC (TNT º = Thermic Neutrality Temperature) and the other 20 at 27 C (HST = Heat Stress Temperature). Far both treatments relative humidity levels averaged 77 % and the photoperiod was 8D:16L with a light intensity of about 40 lux. The animals were fed ad libitum with a commercial pelleted feed. Blood samples were collected from each ammal by intracardiac puncture at 71 and 85 days of age. No interaction effect between temperature and age was found. With regard to effect of temperature, the HST animals had a lower (P&lt;0.01) final body weight (2325 vs 2555 g), daily gain (32. 7 vs 38.1 g) and feed intake (106 vs 126 g/d). The HST treatment significantly (P&lt; 0.05) decreased plasma levels of T (1.01 vs 1.96 ng/ml, DHT (0.42 vs 0.73 ng/ml) and T + DHT (1.43 vs 2.66 ng/ml, but not the T/DHT ratio (2.69). TNT animals had higher (P&lt;0.01) plasma levels of T3 (1.30 vs 1.01 ng/ml) and a lower (P&lt;0.01) T 4/T3 ratio (32. 7 vs 41.3). The concentrations of C (18.9 ng/ml} and r 4 (41.0 ng/ml) resulted unchanged. The etfect of age in the older rabbits was a significantly higher (P&lt;0.01) final body weight (2698 vs 2181 g) daily intake (123 vs 109 g) and feed/gain ratio (3.44 vs 3.12 g/g). No significant difference was observed in plasma concentrations of T (1.48 ng/ml), DHT (0.58 ng/ml), T/DHT (2.69) and T + DHí (2.05 ng/ml} in 71 and 85 days old rabbits. Age had no effect on C levels, which averaged 19.0 ng/ml. In blood samples of younger and older rabb1ts there was no difference in T3 (1.16 ng/ml}, T4 (41.0 ng/ml} values and T4/T3 ratio (37.0). Correlations and linear regression equations were also calculated far daily gain (DG}, digestible energy intake per unit of metabolic body weight (DET/MBW) and each hormone plasma level. Only the thyroid hormones showed significant correlations: T3 was positively (P&lt;0.01) correlated with DG (r = 0.624) and DEI/MBW

Effects of Foliar‐Applied Ethylene Inhibitor and Synthetic Cytokinin on Creeping Bentgrass to Enhance Heat Tolerance

ABSTRACTHeat stress is a major factor causing leaf senescence and other physiological damages in cool‐season grass species. Cytokinins and ethylene are two major plant hormones affecting leaf senescence. The objective of this study was to determine whether foliar application of an ethylene synthesis inhibitor (aminoethoxyvinylglycine, AVG) and a synthetic cytokinin (trans‐zeatin riboside, t‐ZR) would enhance creeping bentgrass (Agrostis stolonifera L.) tolerance to heat stress associated with the suppression of leaf senescence. Creeping bentgrass ‘Penncross’ was exposed to either heat stress (35°C) or optimal growth temperature (20°C) for 35 d in growth chambers. Plants at each temperature were treated with 25 μM AVG, 25 μM t‐ZR or water (control). Foliar spray of AVG or zeatin riboside (ZR) solution resulted in increases in turf quality, leaf chlorophyll content, activities of antioxidant enzymes, and the reduction in lipid peroxidation, compared with water‐treated plants, for plants exposed to heat stress. In addition, foliar application of AVG suppressed ethylene evolution, whereas exogenous ZR resulted in elevated endogenous cytokinin levels under heat stress. The results suggest that the application of AVG or ZR suppressed leaf senescence and improved heat tolerance of creeping bentgrass, which could be because of their effects on endogenous production of ethylene and cytokinins and on antioxidant metabolism.

Structural Dynamics of Archaeal Small Heat Shock Proteins

Small heat shock proteins (sHsps) are a widespread and diverse class of molecular chaperones. In vivo, sHsps contribute to thermotolerance. Recent evidence suggests that their function in the cellular chaperone network is to maintain protein homeostasis by complexing a variety of non-native proteins. One of the most characteristic features of sHsps is their organization into large, sphere-like structures commonly consisting of 12 or 24 subunits. Here, we investigated the functional and structural properties of Hsp20.2, an sHsp from Archaeoglobus fulgidus, in comparison to its relative, Hsp16.5 from Methanocaldococcus jannaschii. Hsp20.2 is active in suppressing the aggregation of different model substrates at physiological and heat-stress temperatures. Electron microscopy showed that Hsp20.2 forms two distinct types of octahedral oligomers of slightly different sizes, indicating certain structural flexibility of the oligomeric assembly. By three-dimensional analysis of electron microscopic images of negatively stained specimens, we were able to reconstitute 3D models of the assemblies at a resolution of 19 Å. Under conditions of heat stress, the distribution of the structurally different Hsp20.2 assemblies changed, and this change was correlated with an increased chaperone activity. In analogy to Hsp20.2, Hsp16.5 oligomers displayed structural dynamics and exhibited increased chaperone activity under conditions of heat stress. Thus, temperature-induced conformational regulation of the activity of sHsps may be a general phenomenon in thermophilic archaea.

Selective Substrate Supply in the Regulation of Yeast de Novo Sphingolipid Synthesis

The heat stress response of Saccharomyces cerevisiae is characterized by transient cell cycle arrest, altered gene expression, degradation of nutrient permeases, trehalose accumulation, and translation initiation of heat shock proteins. Importantly heat stress also induces de novo sphingolipid synthesis upon which many of these subprograms of the heat stress response depend. Despite extensive data addressing the roles for sphingolipids in heat stress, the mechanism(s) by which heat induces sphingolipid synthesis remains unknown. This study was undertaken to determine the events and/or factors required for heat stress-induced sphingolipid synthesis. Data presented indicate that heat does not directly alter the in vitro activity of serine palmitoyltransferase (SPT), the enzyme responsible for initiating de novo sphingolipid synthesis. Moreover deletion of the small peptide Tsc3p, which is thought to maximize SPT activity, specifically reduced production of C(20) sphingolipid species by over 70% but did not significantly decrease overall sphingoid base production. In contrast, the fatty-acid synthase inhibitor cerulenin nearly completely blocked sphingoid base production after heat, indicating a requirement for endogenous fatty acids for heat-mediated sphingoid base synthesis. Consistent with this, genetic studies show that fatty acid import does not contribute to heat-induced de novo synthesis under normal conditions. Interestingly the absence of medium serine also ameliorated heat-induced sphingoid base production, indicating a requirement for exogenous serine for the response, and consistent with this finding, disruption of synthesis of endogenous serine did not affect heat-induced sphingolipid synthesis. Serine uptake assays indicated that heat increased serine uptake from medium by 100% during the first 10 min of heat stress. Moreover treatments that increase serine uptake in the absence of heat including acute medium acidification and glucose treatment also enhanced de novo sphingoid base synthesis equivalent to that induced by heat stress. These data agree with findings from mammalian systems that availability of substrates is a key determinant of flux through sphingolipid synthesis. Moreover data presented here indicate that SPT activity can be driven by several factors that increase serine uptake in the absence of heat. These findings may provide insights into the many systems in which de novo synthesis is increased in the absence of elevated in vitro SPT activity.

Valeur nutritionnelle du son de blé chez le poulet de chair soumis au stress thermique

Commercial broiler were used to compare the apparent metabolisable energy (AME) and crude protein digestibility values of the wheat bran in the chicken exposed to a normal (21°C) environment and to heat stress at 32°C. At 21°C, the AME value of the bran is higher than most values reported by the litterature. This could be due to the high level of starch and the poor level of fibre in our sample of wheat bran. Heat stress temperature resulted in significant (p&lt;0,05) decrease in the AME and protein digestibility of the wheat bran. At 32°C, the AME and digestibility values decrease respectively by -5,6 and -13%. This should be accounted for in the feed processing chain.

Simultaneous determination of protein aggregation, degradation, and absolute molecular weight by size exclusion chromatography–multiangle laser light scattering

The feasibility of size exclusion chromotography (SEC)–multiangle laser-light scattering as a technique to investigate aggregation and degradation of glycosylated and nonglycosylated proteins, and antibodies under various conditions such as addition of detergent, changes in pH, and variation of protein concentration and heat stress temperature was examined. Separation of proteins and their aggregates was performed using SEC–high-performance liquid chromatography. Detection of analytes was carried out with on-line UV, refractive index, and multiangle laser light-scattering detectors. Quantification and molecular weight determination were performed using commercial software. Aggregation and degradation were examined under various conditions and quantitative results are presented for bovine serum albumin, choriogonadotropin, glyceraldehyde-3-phosphate dehydrogenase, Herceptin, and ReoPro. This method can simultaneously determine both the quantities and the molecular weights of macromolecules from a single injection. The determination of molecular weight is absolute which avoids misleading results caused by molecular shape or interactions with the column matrix. This technique is valuable not only for assessing the extent of aggregation but also for effectively monitoring molecule degradation as evidenced by molecular weight reduction and change in monomer amount.

Environmental heat stress, hyperammonemia and nucleotide metabolism during intermittent exercise

This study investigated the influence of environmental heat stress on ammonia (NH3) accumulation in relation to nucleotide metabolism and fatigue during intermittent exercise. Eight males performed 40 min of intermittent exercise (15 s at 306+/-22 W alternating with 15 s of unloaded cycling) followed by five 15 s all-out sprints. Control trials were conducted in a 20 degrees C environment while heat stress trials were performed at an ambient temperature of 40 degrees C. Muscle biopsies and venous blood samples were obtained at rest, after 40 min of exercise and following the maximal sprints. Following exercise with heat stress, the core and muscle temperatures peaked at 39.5+/-0.2 and 40.2+/-0.2 degrees C to be approximately 1 degrees C higher (P<0.05) than the corresponding control values. Mean power output during the five maximal sprints was reduced from 618+/-12 W in control to 558+/-14 W during the heat stress trial (P<0.05). During the hot trial, plasma NH3 increased from 31+/-2 microM at rest to 93+/-6 at 40 min and 151+/-15 microM after the maximal sprints to be 34% higher than control (P<0.05). In contrast, plasma K+ and muscle H+ accumulation were lower (P<0.05) following the maximal sprints with heat stress compared to control, while muscle glycogen, CP, ATP and IMP levels were similar across trials. In conclusion, altered levels of "classical peripheral fatiguing agents" does apparently not explain the reduced capacity for performing repeated sprints following intermittent exercise in the heat, whereas the augmented systemic NH3 response may be a factor influencing fatigue during exercise with superimposed heat stress.

Chaperone-like activity of macrophage migration inhibitory factor

Macrophage migration inhibitory factor is a ubiquitous multifunctional cytokine having diverse immunological and neuroendocrine properties. Although this protein is known to be released into the circulation from the secretory granules of anterior pituitary or directly from immune cells as a consequence of stress, its participation in heat stress-induced aggregation of proteins has not yet been reported. We provide here the first evidence that the macrophage migration inhibitory factor possesses chaperone-like properties. It was shown to exist in the form of a mixture of low and high molecular weight oligomers. At heat stress temperatures the large oligomers dissociate into monomers that bind and stabilize thermally denatured malate dehydrogenase and glycogen phosphorylase b and thus prevent aggregation of the model proteins. Similar chaperone-like effects were also observed in the presence of partially purified brain extract containing besides the macrophage migration inhibitory factor a number of ubiquitous hydrophobic low molecular weight proteins identified by N-terminal microsequence analysis. Being highly stable and hydrophobic, the macrophage migration inhibitory factor in combination with other proteins of similar properties may comprise a family of constitutively expressed “small chaperones” that counteract the early onset of stress, around physiological conditions, when heat shock proteins are not abundant.

Comparison of Gamete Selection for Heat Stress and Cool Temperature Tolerance in Phalaenopsis

Gamete selection was examined as a breeding tool in developing Phalaenopsis hybrids that are more extreme temperature tolerant. Four pairs of hybrid cultivars were cross-pollinated, and then exposed to two temperature extremes, 30 °C/25 °C and 14 °C/9 °C, during initial pollen tube growth. One of each pollinated orchid cultivar was placed in either of two growth chambers and exposed to an 11-hour photoperiod with an irradiance of 180 mmol·m-2·s-1 and a relative humidity of 70% for 3–7 days. The capsules were collected after 150 days. Protocorm development was evaluated after 73 days on a thermogradient table ranging from 10 to 30 °C. For cold-pollinated seeds, protocorm development was optimum at 22 and 28 °C (means of 290 and 250 protocorms per plate, respectively), whereas the greatest protocorm development for warm-pollinated seeds occurred at 20 °C (103 protocorms/plate). Protocorms were evaluated for leaf and root formation 125 days after initial plating. Transfer to warm or cold incubators occurred as seedlings matured. One year after the initial plating, seedlings were evaluated on the following criteria: weight, number of leaves, leaf width, leaf length, leaf area, number of roots, and root length. The pollination treatment significantly affected the number of roots per seedling, whereas table position during germination significantly affected weight. The weight, number of leaves, and average root length were significantly affected by the pollination treatment and incubator interaction. The interaction between pollination treatment and table position significantly affected weight, number of roots, and average root length. Additional replication is required to confirm the greater germinability of cold-pollinated seed at higher temperatures.

Heat stress and age induced maternal effects on wing size and shape in parthenogenetic Drosophila mercatorum

Maternal effects on progeny wing size and shape in a homozygous parthenogenetic strain of Drosophila mercatorum were investigated. The impact of external maternal factors (heat stress) and the impact of internal maternal factors (different maternal and grand maternal age) were studied. The offspring developed under identical environmental conditions, and due to lack of genetic variation any phenotypic difference among offspring could be ascribed to maternal effects. Wing size was estimated by centroid size, shape was analysed with the Procrustes geometric morphometric method and variation in landmark displacement was visualized by principal component analysis. Both kinds of maternal effects had a significant impact on progeny wing size and shape. Maternal heat stress led to the same pattern of response in size and shape among the progeny, with increased difference between the control group and progeny from heat stressed flies in both size and shape with increased maternal heat stress temperature. The effects of maternal age, however, led to different responses in size and shape between the different progeny groups. The observed variation in landmark displacements was similar, and in both cases mainly associated with shape differences of the posterior part of the wing. Finally, our results suggest that maternal effect has some evolutionary implications by altering the genetic correlations among traits, which can affect the response to selective pressures.

Comparison of Gamete Selection for Heat Stress and Cool Temperature Tolerance

Gamete selection was examined as a breeding tool in developing Phalaenopsis hybrids that are more cool or warm temperature tolerant. Four pairs of hybrid cultivars of Phalaenopsis were cross-pollinated, and then exposed to two temperature extremes, 30 °C / 25 °C and 14 °C/9 °C, during pollen tube development and subsequent fertilization. One of each pollinated orchid cultivar was placed in either of two growth chambers and exposed to an 11-h photoperiod with an irradiance of 180 μmol·m-2·s-1 and a relative humidity of 70% during the day and 50% at night for 3-7 days depending on the temperature treatment. The plants were returned to the greenhouse after the initiation of fruit set and the pods were collected after 150 days. Seeds collected from these treatments were surface-sterilized, placed on Phytamax medium and evaluated for protocorm development after 73 days on a thermogradient table ranging from 10 to 30 °C. For the first family for which reciprocal crosses were available, the number of protocorms per plate ranged from 0 in the coldest treatments to 290 at 28 °C. For cold pollinated seeds, protocorm development was optimum at 22 and 28 °C (means of 290 and 250 protocorms per plate, respectively) whereas the greatest protocorm development for warm pollinated seeds occurred at 20 °C (103 protocorms per plate). Of the 1471 total protocorms scored, 1095 were from cold pollinations, whereas 376 were from the warm pollinations. Additional replication is required to confirm the greater germinability of cold-pollinated seed at higher temperatures.

Some physiological changes in strawberry (Fragaria × ananassa ‘Camarosa’) plants under heat stress

SummaryThe effects of heat injury induced by long exposures were evaluated in strawberry (Fragaria × ananassa ‘plants’) Camarosa in this study. Seedlings were grown in 14 × 12 cm pots using perlite for three weeks at 25/10°C day/night temperature, and watered daily by modified 1/3 Hoagland nutrient solution. Half of the plants were transferred to a growth chamber with a constant 25°C, 16/8 h (light/dark) photoperiod regime and 1200 lux light intensity for a week to acclimate the plants. Temperature was increased stepwise (5 K per 48 h) to 30, 35, 40°C and finally to 45°C. In addition to others, plants were transferred from the outside to the growth chamber, at each temperature step to impose a heat shock. Leaf relative water content (RWC, %), loss of turgidity, chlorophyll content (Spad value) and heat-stress tolerance (HTS; LT50) were measured in control and stressed plants. Total soluble proteins and total DNA were extracted from the leaves following the above treatments using standard procedures and total protein contents were determined using a Bradford assay. In general, effects of gradual heat stress (GHS) and shock heat stress (SHS) on the variables studied were mostly significant, except for chlorophyll content, while the effect of temperatures was significant for all the variables. Interaction between the heat stress type and temperature treatments was not significant for leaf RWC, loss of turgidity and chlorophyll content. Data also indicated that total protein and DNA contents were changed significantly by heat stress types (GHS and SHS) and/or temperature treatments. The plants exposed to GHS exhibited a significant increase in HST compared with the plants exposed to SHS (LT50 of 41.5°C and 39°C, respectively). Consequently, gradual heat stress increased HST in strawberry leaves. Increased HST may be associated with the accumulation of several heat-stable proteins in GHS plants.

Effects of heat stress on cognitive performance: the current state of knowledge

This paper discusses the current state of knowledge on the effects of heat stress on cognitive performance. Although substantial research has been performed, it has proven difficult to describe the literature findings in a systematic manner. This is due to the large number of factors that come into play, such as task type, exposure duration, skill and acclimatization level of the individual and due to the absence of a concise theory on which experimental work can be based. However, two trends have been identified. First, heat stress affects cognitive performance differentially, depending on the type of cognitive task. Secondly, it appears that a relationship can be established between the effects of heat stress and deep body temperature. A number of exposure limits have been proposed during the last decades. These limits are summarized in this paper, with a special emphasis on the most recent one derived by Hancock and Vasmatzidis. This limit, which employs an attentional resource approach, defines exposure duration thresholds as parallel lines. Although this approach appears to be the most promising thus far, it is concluded that much remains to be understood before a limit becomes universally acceptable.

Water Temperature, Predation, and the Neglected Role of Physiological Rate Effects in Rocky Intertidal Communities

Ecologists and physiologists working on rocky shores have emphasized the effects of environmental stress on the distribution of intertidal organisms. Although consumer stress models suggest that physical extremes may often reduce predation and herbivory through negative impacts on the physiological performance of consumers, few field studies have rigorously tested how environmental variation affects feeding rates. I review and analyze field experiments that quantified per capita feeding rates of a keystone predator, the sea star Pisaster ochraceus, in relation to aerial heat stress, wave forces, and water temperature at three rocky intertidal sites on the Oregon coast. Predation rates during 14-day periods were unrelated to aerial temperature, but decreased significantly with decreasing water temperature. There was suggestive but inconclusive evidence that predation rates also declined with increasing wave forces. Data-logger records suggested that thermal stress was rare in the wave-exposed habitats that I studied; sea star body temperatures likely reached warm levels (>24°C) on only 9 dates in 3 yr. In contrast, wind-driven upwelling regularly generated 3 to 5°C fluctuations in water temperature, and field and laboratory results suggest that such changes significantly alter feeding rates of Pisaster. These physiological rate effects, near the center of an organism's thermal range, may not reduce growth or fitness, and thus are distinct from the effects of environmental stress. This study underscores the need to consider organismal responses both under "normal" conditions, as well as under extreme conditions. Examining both kinds of responses is necessary to understand how different components of environmental variation regulate physiological performance and the strength of species interactions in intertidal communities.